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Vitamin D and the Athlete: Risks, Recommendations, and Benefits

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Vitamin D is well known for its role in calcium regulation and bone health, but emerging literature tells of vitamin D's central role in other vital body processes, such as: signaling gene response, protein synthesis, hormone synthesis, immune response, plus, cell turnover and regeneration. The discovery of the vitamin D receptor within the muscle suggested a significant role for vitamin D in muscle tissue function. This discovery led researchers to question the impact that vitamin D deficiency could have on athletic performance and injury. With over 77% of the general population considered vitamin D insufficient, it's likely that many athletes fall into the same category. Research has suggested vitamin D to have a significant effect on muscle weakness, pain, balance, and fractures in the aging population; still, the athletic population is yet to be fully examined. There are few studies to date that have examined the relationship between vitamin D status and performance, therefore, this review will focus on the bodily roles of vitamin D, recommended 25(OH)D levels, vitamin D intake guidelines and risk factors for vitamin D insufficiency in athletes. In addition, the preliminary findings regarding vitamin D's impact on athletic performance will be examined.
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Nutrients 2013, 5, 1856-1868; doi:10.3390/nu5061856
nutrients
ISSN 2072-6643
www.mdpi.com/journal/nutrients
Review
Vitamin D and the Athlete: Risks, Recommendations,
and Benefits
Dana Ogan * and Kelly Pritchett
Department of Nutrition, Exercise and Health Science, Central Washington University,
400 E. University Way, Ellensburg, WA 98926, USA; E-Mail: kkerr@cwu.edu
* Author to whom correspondence should be addressed; E-Mail: danastorlie@yahoo.com;
Tel.: +1-425-345-0970; Fax: +1-509-963-1848.
Received: 2 April 2013; in revised form: 7 May 2013 / Accepted: 8 May 2013 /
Published: 28 May 2013
Abstract: Vitamin D is well known for its role in calcium regulation and bone health, but
emerging literature tells of vitamin D’s central role in other vital body processes, such as:
signaling gene response, protein synthesis, hormone synthesis, immune response, plus, cell
turnover and regeneration. The discovery of the vitamin D receptor within the muscle
suggested a significant role for vitamin D in muscle tissue function. This discovery led
researchers to question the impact that vitamin D deficiency could have on athletic
performance and injury. With over 77% of the general population considered vitamin D
insufficient, it’s likely that many athletes fall into the same category. Research has
suggested vitamin D to have a significant effect on muscle weakness, pain, balance, and
fractures in the aging population; still, the athletic population is yet to be fully examined.
There are few studies to date that have examined the relationship between vitamin D status
and performance, therefore, this review will focus on the bodily roles of vitamin D,
recommended 25(OH)D levels, vitamin D intake guidelines and risk factors for vitamin D
insufficiency in athletes. In addition, the preliminary findings regarding vitamin D’s impact
on athletic performance will be examined.
Keywords: vitamin D; athletic performance; 25(OH)D; supplementation; insufficiency; athlete
OPEN ACCESS
Nutrients 2013, 5 1857
1. Introduction
As research has progressed, the importance and versatility of vitamin D in the body has become
quite evident, therefore the prevalence of vitamin D insufficiency has been heavily examined in recent
years. Research suggests vitamin D’s active role in immune function, protein synthesis, muscle
function, inflammatory response, cellular growth and regulation of skeletal muscle [14]. In addition, a
common symptom of clinical vitamin D deficiency is muscle weakness. Due to the many essential
roles of vitamin D within the body, it has been suggested that physical performance may be influenced
by serum vitamin D status, especially in those who are clinically deficient.
Vitamin D insufficiencies are estimated to affect over one billion people worldwide [5]. The Third
National Health and Nutrition Examination Survey (NHANES III) data showed a significant increase
in vitamin D insufficiency in the USA over the last 30 years, with over 77% of Americans considered
vitamin D insufficient [6]. The alarming rates of insufficiency and the vast metabolic properties of
vitamin D have led researchers to examine the influence of vitamin D, not only on disease prevention,
but also on physical performance and injury. Vitamin D has been identified in most tissues within the
body, including skeletal muscle, which has led to further examination of vitamin D’s influence on
athletes and physical performance.
Because athletes and sports medicine physicians are primarily concerned with performance, the risk
of vitamin D insufficiency among athletes has received growing interest and is under current
examination by many researchers. In the last decade, researchers have examined 25(OH)D levels
among various groups of athletes, ranging from gymnasts to runners to jockeys. Some findings have
suggested that vitamin D levels in athletes are comparable to those of the general population; however,
results depended largely on geographical location and type of sport (indoor vs. outdoor). It is apparent
that the athlete is at an equal risk for vitamin D insufficiency, therefore the potential impact of vitamin
D status on performance is now under examination. There are few studies to date that have examined
the relationship between vitamin D status and performance, therefore, this review will focus on the
bodily roles of vitamin D, recommended serum 25(OH)D level, vitamin D intake guidelines and risk
factors for vitamin D insufficiency in athletes. In addition, the preliminary findings regarding vitamin
D’s impact on athletic performance will be examined.
2. Physiology & Bone Health
Vitamin D functions in two distinct ways within the body, through endocrine and autocrine
mechanisms. The first, and most well-known, mechanism is the endocrine function, which enhances
intestinal calcium absorption and osteoclast activity [1]. Vitamin D is essential for bone growth,
density and remodeling, and without adequate amounts, bone loss or injury will occur [7]. When
vitamin D is low, parathyroid hormone (PTH) increases to activate bone resorption in order to satisfy
the body’s demand for calcium [8]. Low vitamin D increases bone turnover, which increases the risk
for a bone injury, like a stress fracture.
A study examining male Finnish military recruits found vitamin D status to be a significant
determinant of maximal peak bone mass and also discovered that 25(OH)D levels below 30 ng/mL
significantly increased the risk of stress fractures in this subject group [9]. In a large (n = 3700)
Nutrients 2013, 5 1858
vitamin D supplementation trial using female navy recruits, subjects receiving 800 IU/day of vitamin D
for eight weeks, had a 20% lower incidence in stress fractures than the placebo group [8]. These
studies in active populations, such as military recruits, display the critical role that vitamin D plays in
optimal bone health. These findings also suggest that sufficient vitamin D status may prevent injuries,
such as stress fractures. Stress fractures are quite common among athletes; most commonly seen
among track and field sports, in up to 10%31% of athletes [8]. Stress fractures can significantly
influence performance due to debilitating pain and even cause permanent disability [8].
Vitamin D’s other pathway is the autocrine pathway. It is less recognized, but many essential
metabolic processes take place in this pathway. On a daily basis, over 80% of the vitamin D within the
body is utilized through the autocrine pathway [10]. The autocrine pathway is involved in essential
body processes like signaling gene response/expression, synthesizing proteins, hormone synthesis,
immune/inflammatory response, plus, cell turnover and synthesis [10]. “Without vitamin D, the ability
of the cell to respond adequately to pathologic and physiologic signals is impaired” [10].
3. Vitamin D and Muscle Tissue
The autocrine pathway appears to be of utmost importance and has recently received a great deal of
attention in regards to vitamin D’s influence on skeletal muscle function [11]. Vitamin D receptor
(VDR) sites have been identified in virtually every tissue within the body [12]. VDR regulates
expression in hundreds of genes that perform essential bodily functions. The discovery of VDR within
the muscle suggested a significant role for vitamin D in muscle tissue and has since been identified as
a regulator of skeletal muscle [3,11,1316]. There are two proposed mechanisms by which vitamin D
status may influence muscular strength. One possible explanation involves the direct role of
1,25-dihydroxyvitamin D [1,25(OH)
2
D] on VDRs within the muscle cells [11,17,18]. A second
explanation suggests that vitamin D modifies the transportation of calcium in the sarcoplasmic
reticulum by increasing the efficiency or number of calcium binding sites involved in muscle
contraction. This indirect mechanism however, has only been examined in rat models [11]. On the
contrary, one study disputes the evidence for the presence of VDRs within the skeletal muscle cells
and suggests that the immunocytochemical staining to detect VDR may be responsible for the false
positives results in previous studies [18,19].
Furthermore, it has been suggested that vitamin D supplementation in individuals with low vitamin
D status may improve muscle strength. This is believed to be due to an increase in the size and amount
of type II (fast twitch) muscle fibers associated with vitamin D supplementation [11,20]. It should be
noted that type II fibers are predominant in power and anaerobic activities, and are recruited first to
prevent falls, associated with muscle strength in the aging population [11].
Various researchers have found vitamin D to have a significant effect on muscle weakness, pain,
balance and fractures in aging individuals [3,4]. It is difficult, however to compare the results given the
variety of outcome measures and differences in populations used in the studies [14]. Several
observational studies have suggested that vitamin D status influences muscular strength and function in
the elderly [11,21]. Contrary to these findings, Chan et al., (2012) found no association between
baseline vitamin D status and changes in performance measures over a four year period [14,22].
Nutrients 2013, 5 1859
Replacing vitamin D stores in the elderly population may be protective against fall risk and declining
physical function [11,14].
Few studies to date have examined this relationship in the adolescent population. Foo et al. (2009)
examined the relationship between 25(OH)D status and bone mass, bone turnover, and muscle strength
in Chinese adolescent females (n = 301) and found that poor vitamin D status (<20 ng/mL) was
associated with reduced forearm strength, (using a handgrip dynanmometer) when compared to
individuals with adequate vitamin D levels (>20 ng/mL) [17]. Ward et al. (2004) suggested that
25(OH)D levels were positively associated with muscle power, and jump height in postmenarchal
females (n = 91), however physical activity levels were not taken into consideration [11,23].
These findings in regard to muscle tissue and function suggest that vitamin D status may have a
significant effect on muscle performance and injury prevention, therefore possibly influencing athletic
performance. However, further research is warranted to determine the magnitude of effect of vitamin
D on muscle strength and performance.
4. Vitamin D Recommendations (Intake and Desirable Levels)
Although the sun is the most plentiful source of vitamin D, there are also some dietary sources.
Some common foods contain significant levels of vitamin D, naturally, including salmon, fatty fish,
egg yolks, plus, fortified products also exist, such as, milk, cereal and orange juice [24]. While these
dietary sources may appear significant, the process of absorbing dietary vitamin D is only about 50%
efficient; therefore, much of the nutrient value is lost in digestion [25]. The lack of dietary vitamin D is
yet another factor that increases the risk of vitamin D insufficiency. Most experts agree that a higher
intake of vitamin D, through dietary sources, ultraviolet B (UVB) exposure, and supplementation, is
necessary to obtain optimal serum vitamin D levels [10,2628].
In November of 2010, the Institute of Medicine (IOM) released new recommendations for dietary
intake of vitamin D, 400600 IU/day for children & adults (070 years), 800 IU/day for older adults
(>70 years) [29]. These values are only slightly higher than past recommendations [29]. Many experts
argue that while IOM intake recommendations may adequately prevent clinical vitamin D deficiency,
they are significantly lower than the level necessary to achieve optimal vitamin D status [5,6,10,26].
The Recommended Dietary Allowance (RDA) for Vitamin D, according to the National Institute of
Medicine (IOM) [29] is compared to the Endocrine Society’s [30] recommended intake in Table 1.
Many believe that the RDA is grossly underestimated [5,6,10,26], including the Endocrine Society,
who released vitamin intake guidelines that are significantly higher [30]. The Endocrine Society
recommends 4001000 IU/day for infants, 6001000 IU/day in children (118 years) and
15002000 IU/day in adults, in addition to sensible sun exposure [30].
Another area of debate among vitamin D researchers is the terminology and reference values used
to define optimal vitamin D status, deficiency, and insufficiency. Optimal serum 25(OH)D
concentrations have yet to be defined; however, most researchers have similar reference values [31].
Vitamin D deficiency is often defined as <20 ng/mL (50 nmol/L), and insufficiency defined as
2032 ng/mL (5080 nmol/L) and optimal levels are >40 ng/mL (100 nmol/L) [5,10,12,32]. The term
insufficiency “appears to be the currently favored term for the range of marginal deficiency and is the
theoretical serum concentration that is not high enough to protect against certain chronic diseases” [32].
Nutrients 2013, 5 1860
Table 1. Recommended vitamin D intake levels of the Institute of Medicine vs. Endocrine
Society [29,30].
Age
Recommended Intake (IU/day)
Upper Limit (IU/day)
National Institute of Medicine
Children (018 years)
400600
2500 (13 years)
3000 (48 years)
4000 (1318 years)
Adults (1970 years)
600
4000
Older Adults (>70 years)
800
4000
Pregnancy/Lactation
600
4000
The Endocrine Society
Children (018 years)
4001000
20004000
Adults (1970 years)
15002000
10,000
Older Adults (>70 years)
15002000
10,000
Pregnancy/Lactation
6001000 (1418 years)
15002000 (1950 years)
10,000
Optimal levels of serum 25(OH)D are no exception to the controversy. When serum levels reach
>32 ng/mL, parathyroid hormone (PTH) levels become stable and reduce the risk of secondary
hypoparathyroidism, which is commonly associated with low vitamin D status. In addition, intestinal
calcium absorption is enhanced, reducing the risk of secondary bone disease [5,28]. These basic
vitamin D functions are efficiently demonstrated at 25(OH)D levels >32 ng/mL; however, superior
benefits are observed at even greater levels. For example, only at 25(OH)D levels >40 ng/mL, does
vitamin D begin to be stored in the muscle and fat for future use [20,28]. Therefore, at levels
<40 ng/mL, the body relies on a daily replenishment of vitamin D to directly satisfy its daily
requirements, which is not likely to be present in the common diet. At levels <40 ng/mL, there appears
to be just enough circulating 25(OH)D available for all of the immediate metabolic needs; however,
stored vitamin D is not likely available for the advanced processes involved in the critical autocrine
pathways [20].
It is estimated that the body requires 30005000 IU of vitamin D per day to meet the needs of
“essentially every tissue and cell in the body” [12]. The IOM recommends 600 IU of vitamin D
for most adults (1870 years of age) to prevent clinical vitamin D deficiency, defined as
25(OH)D 20 ng/mL [29]. In contrast, most expert’s recommendations are much higher than 600 IU
per day, because their recommendations are designed to help reach optimal 25(OH)D levels of at least
40 ng/mL. Intake levels recommended by most experts not only allow support for daily metabolic
requirements, but also allow for vitamin D storage and increased availability, which appears to reduce
the risk of many diseases and possibly enhance performance. The recommended daily vitamin D
intake, according to most experts, is at least 1000 IU per day to maintain optimal 25(OH)D status;
however, more is required if levels begin suboptimal [5,10,28]. With over 77% of Americans considered
insufficient in vitamin D, it is apparent that the current recommendations are suboptimal [5,6,10,26].
Intake recommendations increase with age, pregnancy, and lactation. In addition, experts recommend
much higher initial dosages if 25(OH)D levels begin deficient, ranging from 2000 to 200,000 IU, until
optimal 25(OH)D levels are met, then 10002000 IU/day for maintenance [5,28,32]. A commonly
Nutrients 2013, 5 1861
prescribed treatment to quickly correct vitamin D deficiency is a weekly dose of 50,000 IU of vitamin D
for eight weeks [12].
The tolerable upper limit for vitamin D has been set by the IOM at 4000 IU for adults, compared to
10,000 IU/day by the Endocrine Society [29,30] (Table 1). Leading experts have claimed that a daily
intake of 10,000 IU would take months, or even years to manifest symptoms of toxicity [28]. A recent
publication found no cases of toxicity with daily intakes of 30,000 IU per day for an extended period
of time [10]. Regardless of the current dietary intake value, the amount of vitamin D produced from
15 min of unprotected sun exposure is 10,000 to 20,000 IU, in a light-skinned individual, making most
experts believe toxicity to be a rare and unlikely event [10,12]. During the months that UVB rays are
available from the sun, five to 15 min of unprotected sun exposure between the hours of 10 a.m. and
3 p.m. appear to provide adequate amounts of vitamin D [12].
There have never been any reported cases of vitamin D toxicity from over exposure to the sun;
however, symptoms of intoxication, such as hypercalcemia, have been observed when 25(OH)D levels
are greater than 150 ng/mL [12]. Serum 25(OH)D levels in individuals living close to the equator and
working outdoors are often around 50 ng/mL, supporting the theory that vitamin D toxicity from
the sun is extremely unlikely, and suggesting that any toxicities would result only from over
supplementation [28]. Regardless, many experts agree than 1000 IU/day in the absence of proper sun
exposure can maintain 25(OH)D levels of at least 32 ng/mL [12].
5. Vitamin D Status of Athletes
The distance from the equator, season, and time of day dictate whether vitamin D is available from
the sun. Production of vitamin D from the sun is also dictated by cloud cover, pollution, sunblock, skin
pigment and age. During the summer months, UVB radiation from the sun can be absorbed in adequate
amounts to synthesize vitamin D [5]. However, during winter months, the angle of the sun prevents
UVB radiation from reaching latitudes greater than 3537 degrees, therefore, vitamin D cannot be
synthesized from in these areas [5,20].
Research has suggested that low levels of vitamin D are widespread in populations living south of
the 35th parallel [26]. Even if one spends ample time in the sun, sunscreen with a sun protection factor
(SPF) of 15 results in a 99% decrease in vitamin D absorption [5]. Individuals who spend ample time
outdoors may still need vitamin D supplementation to maintain adequate levels during the winter [33,34].
Many outdoor athletes avoid peak sunlight hours, opting to practice early in the morning or late at
night, which greatly reduces UVB exposure, putting them at considerable risk of vitamin D
insufficiency. Various studies have found many athletes to be at high risk for vitamin D insufficiencies.
Table 2 displays prevalence of vitamin D insufficiencies among diverse athletic groups.
Hamilton et al. (2009) revealed that 90% of Middle Eastern sportsmen were vitamin D deficient
between April and October [33]. Although these sportsmen were training at favorable latitudes, Qatar
(25.4°N), they averaged less than 30 min of sun exposure per day. Another study conducted at
favorable latitude (Israel 31.8°N), suggested that 73% of athletes were vitamin D insufficient [35]. The
majority (83%) of female, Australian indoor athletes were also found to be vitamin D insufficient [36].
In contrast, a study conducted at less favorable latitude (Laramie, WY 41.3°N), revealed vitamin D
insufficiency in 63% of indoor/outdoor athletes during winter, compared to the fall (12%) and spring
Nutrients 2013, 5 1862
(20%) in indoor and outdoor athletes [37]. Finally, a study conducted even further from the equator
(Ellensburg, WA 46.9N), using exclusively outdoor athletes, found 25%30% with vitamin D
insufficiency from fall to winter [38]. Storlie et al. suggested that 1000 IU/day of vitamin D was not
enough to prevent seasonal decline of vitamin D status in this cohort [38]. Although the results are
variable, geographical location (latitude) and gender do not appear to be the major risk factors for
vitamin D insufficiency in athletes. Lack of sun exposure appears to be the main risk factor, putting
indoor athletes and those who avoid peak daylight hours, regardless of latitudinal location, at the
greatest risk for vitamin D insufficiency [2,9,33,3538].
Table 2. Prevalence of Vitamin D deficiency (<20 ng/mL) and insufficiency (<32 ng/mL)
in various athletic populations.
Type of Athlete
Gender
Vitamin D Status
Reference
Finnish military recruits
Male
39% deficient
Valimaki et al. [8]
UK professional athletes
(jockeys, rugby, soccer)
Male
62% deficient
Close et al. [39]
UK athletes (football, rugby)
Male
57% deficient
Close et al. [40]
Middle Eastern sportsman
Male
32% insufficient
58% deficient
Hamilton et al. [33]
Australian gymnasts
Female
33% insufficient
Lovell [36]
Israeli athletes & dancers
Male & Female
73% insufficient
Constantini et al. [35]
USA indoor/outdoor athletes
Male & Female
12% insufficient
Halliday et al. [37]
USA endurance athletes (runners)
Male & Female
42% insufficient
11% deficient
Willis et al. [2]
USA outdoor athletes (rugby,
football, track, cross country)
Male
25% insufficient
Storlie et al. [38]
6. Vitamin D and Athletic Performance
Original research concerning vitamin D and athletic performance dates back to the early twentieth
century, but current performance trials are quite limited and inconclusive. Russian and German
researchers were the first to report the convincing effects of ultraviolet light irradiation for improving
athletic performance and decreasing chronic sports related pain [20]. These early European researchers
suggested significant improvements in time trials, cardiovascular fitness, and strength with treatment
of UVB irradiation prior to performance [20]. German Olympic officials considered these effects
significant enough for UVB radiation (vitamin D) to be considered an ergogenic aid. In support of this
concept, many athletes claim to peak in physical fitness during the time of year that vitamin D (UVB)
levels are at their highest, summer and fall [20].
Unfortunately, there are limited experimental studies available and even fewer that demonstrate a
performance enhancement from vitamin D supplementation. However, research examining the aging
population (>65 years of age) suggests benefits from vitamin D supplementation. Multiple
performance studies in older adults have related low vitamin D levels to decreased reaction time, poor
balance, and an increased risk of falling [3]. Furthermore, vitamin D supplementation (800 IU/ day) in
older adults showed improvements in strength, and walking distance, and a decrease in general
Nutrients 2013, 5 1863
discomfort [3]. These favorable results in older adults support the need for further research on athletic
performance and vitamin D.
The current research available to support vitamin D’s influence on performance is quite limited.
An (n = 39), unpublished thesis examined 25(OH)D and maximal oxygen uptake (VO
2
max) to
determine vitamin D’s effect on aerobic fitness in physically active college males [41]. Higher
25(OH)D levels were associated with an increased VO2max, compared to those with lower vitamin D
levels (p < 0.01) [41]. These findings suggest that a favorable vitamin D status may improve
aerobic performance.
Close et al. (2013) examined, young, United Kingdom (UK, 53°N) based athletes (n = 30), and
examined the effects that vitamin D supplementation (2040,000 IU/week for 12 weeks) had on
muscle performance (1-RM bench press, leg press and vertical jump height) [39]. Subjects were
assigned to a placebo, 20,000 IU/week or 40,000 IU/week of vitamin D for 12 weeks. Muscle
performance and 25(OH)D was measured at six and 12 weeks, revealing that six weeks of
supplementation was enough to correct vitamin D deficiency, however, it was not enough to obtain
optimal vitamin D levels >40 ng/mL [39]. Contrary to the findings in the elderly population, no
significant improvements in muscle performance were observed after 6 or 12 weeks of vitamin D
supplementation, although serum 25(OH)D levels significantly increased over this time, from an
average of 20.43 ng/mL to 31.6539.26 ng/mL [39]. In this study, lower baseline concentrations
appeared to respond greater to supplementation, therefore, future studies may find more substantial
results by dividing subjects into groups based on their baseline levels.
Although final 25(OH)D concentrations obtained by the athletes were no longer considered
deficient (>20 ng/mL), researchers hypothesized that higher total serum levels may be necessary to
document enhanced muscle performance in young athletes [8,39]. According to Close et al. (2013),
higher 25(OH)D levels may be necessary to induce a physiological response within skeletal
muscle [39]. To explain the lack of response, the author suggested that skeletal muscle may require
higher serum concentrations for a response, compared to other tissues [39]. The significant response
shown in elderly subjects, however, may be explained by sarcopenia. If the elderly were actively
losing muscle mass, they may have a more sensitive response to vitamin D supplementation in the
skeletal muscle [39]. The authors suggested that more convincing results may be observed by giving
supplemental doses of vitamin D to increase serum 25(OH)D above 40 ng/mL.
A larger (n = 61 athletes, n = 31 healthy control subjects) UK-based vitamin D supplementation
trial resulted in higher mean 25(OH)D levels, as a result of 5000 IU/day of vitamin D3 for eight weeks
and found promising muscle performance results [40]. This supplementation regime significantly
increased mean 25(OH)D levels from (mean ± SD) 11.62 ± 10.02 ng/mL to 41.27 ± 10.02 ng/mL,
whereas a placebo group showed no significant changes. The supplementation group also displayed
significant improvements (p = 0.008) in 10-meter sprint times and vertical jump (with no improvements
in 1-RM bench and squat tests) compared to the placebo group [40]. One athlete’s 25(OH)D levels
increased from 22.40 ng/mL to 55.69 ng/mL and showed improvements in all performance areas, this
is only one athlete however. These findings support the aforementioned hypothesis that higher serum
25(OH)D levels (>40 ng/mL) may generate more convincing performance improvements [40].
Findings also suggest that a daily dose of vitamin D (5000 IU/day) may be superior in raising
25(OH)D levels when compared to a weekly dose (40,000 IU/week) [39,40]. Based off of these two
Nutrients 2013, 5 1864
preliminary studies and guidelines from leading experts, 25(OH)D levels above 40 ng/mL are likely
necessary to significantly improve anaerobic athletic performance. There are no studies available that
have examined the effect of vitamin D on aerobic or endurance athletic performance.
To maintain 25(OH)D levels of 40 ng/mL, vitamin D supplementation, especially during the
winter months, is warranted [20,28,39,40]. The 25(OH)D goal of 40 ng/mL is recommended for
athletes because at this level, vitamin D begins to be stored in the muscle and fat for future use.
Furthermore, at levels below 32 ng/mL, vitamin D is not likely to be readily available for the advanced
processes involved in the autocrine pathways, which is the pathway that is most likely to influence
performance [20,25]. This level is also supported by the two comparable Close et al. studies,
where the study achieving 25(OH)D levels greater than 40 ng/mL showed significant effects on
performance [39,40].
Besides the two UK based performance trials [39,40], recent research on vitamin D and athletes has
focused on the prevalence of vitamin D insufficiency among athletes, not the effects on performance.
Although performance trials are limited, various other studies have resulted in alternative findings to
support vitamin D’s positive impact on performance. Willis et al. (2012) revealed that decreased
vitamin D was associated with an increased marker for inflammation in endurance athletes [2]. These
results call for future investigation to determine whether decreased vitamin D may increase the risk for
inflammatory-related injuries [2]. Razavi et al. (2011) found that vitamin D and aerobic exercise
improved exercise tolerance in asthmatic patients (compared to a control, only aerobic exercise or only
vitamin D supplementation groups), suggesting that vitamin D and aerobic exercise together, may
provide anti-inflammatory effects within the lungs [42].
As previously mentioned, the body requires an estimated 30005000 IU/day of vitamin D and the
high levels of physical activity in athletes may result in increased physiological demands for
vitamin D [12]. Since vitamin D is actively used in many metabolic pathways, it is possible that the
athlete may require increased intake of vitamin D to assure adequate availability and storage for
optimal performance [32]. This hypothesis may explain the lack of response observed from Close et al.,
when 25(OH)D levels above 40 ng/mL were not achieved and may also support increased vitamin D
intake recommendations for athletes [40]. At this point, the appropriate vitamin D supplementation
regime for athletes appears to depend on current 25(OH)D levels, season and sun exposure, with the
goal of >40 ng/mL in mind. Considering these factors, many athletes, especially indoor athletes and
those who are insufficient, will require up to 5000 IU of vitamin D/day for eight weeks, to reach
40 ng/mL, then 10002000 IU/day for maintenance.
Although the results of performance trials are not yet convincing enough to support vitamin D as a
direct performance enhancer, obtaining optimal 25(OH)D levels can reduce the risk of debilitating
stress fracture among athletes, which may indirectly influence performance through prevention of
injury [8,9]. In addition, because of its active role in muscle, resolution of vitamin D insufficiency has
the potential to impact performance [11,14].
Nutrients 2013, 5 1865
7. Conclusion
Vitamin D is established as a major factor in preventing stress factors and optimizing bone health,
both of which are of great importance to the athlete [8,9]. Rates of vitamin D insufficiency in athletes
vary among studies, but most researchers agree that athletes should be evaluated regarding vitamin D
status and given intake recommendations to maintain optimal 25(OH)D levels >40 ng/mL. Not only
does vitamin D assist in growth and maintenance of the bone, but it also aids in regulation of
electrolyte metabolism, protein synthesis, gene expression, and immune function [10,28]. These vital
functions are essential for all individuals, especially the elite and recreational athlete. Therefore,
regardless of the limited literature available in support of a positive effect from vitamin D on
performance, obtaining optimal 25(OH)D levels should be a goal for all athletes.
The data are not conclusive to support vitamin D supplementation as a direct performance enhancer,
however, research supports the role of vitamin D in the prevention of chronic and acute diseases, such
as: cancer, cardiovascular disease, type 2 diabetes, autoimmune diseases and infectious diseases [18].
Athlete or not, optimal vitamin D status is essential to countless fundamental body functions, making it
important for all individuals to obtain appropriate levels. Further research is warranted to appropriately
define supplementation regimes for specific populations (elderly, athletes, those who are deficient,
altering levels for the seasons), establish definite serum 25(OH)D goals, and investigate the effect of
vitamin D on physical performance, especially endurance training.
While there is still limited evidence to support vitamin D as a performance enhancer, sports
physicians should consider the importance of optimal vitamin D status to prevent stress fractures and
muscle injury. Further research is warranted to determine the magnitude of effect from vitamin D on
muscle strength and performance. Based off of the prevalence data, high-risk athletes, such as indoor
athletes and those who avoid peak daylight hours, should have 25(OH)D levels assessed annually.
Conflict of Interest
The authors declare no conflict of interest.
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© 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).
... Vitamin D also regulates muscle contractile function [15]. It is suggested that the status of the bioactive form of vitamin D and the expression of VDR in muscle cells seem to be key factors involved in calcium-binding efficiency for muscle fiber twitch [16]. The mechanism by which vitamin D may improve aerobic performance remains unclear. ...
... A high prevalence of vitamin D deficiency has been recorded in various groups of professional athletes during regular high-intensity training [16,[23][24][25][26][27]. This almost pandemic deficiency is believed to be related to intensive physical activity, higher metabolic rate, frequent indoor training, and lack of sufficient exposure to sunlight [28,29]. ...
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The aim of this study was to determine whether supplementation with vitamin D during eight weeks of high-intensity training influences muscle power and aerobic performance in young soccer players. A total of 25 athletes were divided into two groups: the supplemented group (GS; n = 12; vitamin D 20,000 IU, twice a week) and the non-supplemented group (GN; n = 13). A set of measurements, including sprint tests, explosive power test, maximal oxygen uptake (VO2max), and serum 25(OH)D concentration, were obtained before (T1) and after (T2) the intervention. A significant group x time interaction was found in the 25(OH)D serum levels (p = 0.002; ES = 0.36, large). A significant improvement in VO2max was found in the TG (p = 0.0004) and the GS (p = 0.031). Moreover, a positive correlation between 25(OH)D and VO2max (R = 0.4192, p = 0.0024) was calculated. The explosive power tests revealed insignificant time interactions in the average 10-jump height and average 10-jump power (p = 0.07, ES = 0.13; p = 0.10, ES = 0.11, respectively). A statistically insignificant trend was observed only in the group-by-time interaction for the sprint of 10 m (p = 0.05; ES = 0.15, large). The present study provides evidence that vitamin D supplementation has a positive but trivial impact on the explosive power and locomotor skills of young soccer players, but could significantly affect their aerobic performance.
... In the past there are many researches which were done analyzing the vitamin D deficiency in a geographical area [1]. Ogan Det.al concluded that Vitamin D deficiency is very prevalent among both non-athletes and athletes, and this nutrient is suggested to play a very vital role in their health and performance [2]. Halliday T.M et.al reported that vitamin D was inadequate among 56% of the athletes worldwide. ...
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This is an Open Access Journal / article distributed under the terms of the Creative Commons Attribution License (CC BY-NC-ND 3.0) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. All rights reserved. The objective of the study is to find the prevalence of vitamin D deficiency in athletes living in Kozhikode and Malappuram districts of Kerala State in India. 220 subjects belonging to age group 15-30 years old were screened for inclusion and exclusion criteria and 97 subjects were taken into the Cross-sectional study. Anthropometric assessment and Blood analysis for Vitamin D and Calcium was done on them and among them 73 subjects had insufficient/deficient Vitamin D level were the actual samples for cross sectional study. The data collection spanned for 6 months (March-August 2018). Among 97 subjects screened, a genera prevalence of 77%of Vitamin D insufficiency (<30 ng/ml) was observed in male and 71% among female athletes in selected districts of Kerala, India. Among this 73 subjects 27% had Vitamin D deficiency (< 20 ng/ml). Significant correlation between Vitamin D deficiency and serum calcium levels of the athletes was established with P value <.001. No statistically significant correlation between 25(OH)D levels and sun exposure, physical activity, practice area or anthropometric levels could be established. The study concluded that healthy male and female athletes in Kerala have a high prevalence of vitamin D deficiency. The results of this study suggest that there is a need for regular supplementation and vitamin D awareness campaigns for athletes in Kerala, India. ABSTRACT RESEARCH ARTICLE
... Yet despite this serious concern of skin cancer, most of the athletes' practices in the sun, but they heavily depend on the sun screen lotions for protecting the skin form UVR which they consider the major risk factor for their risk of skin cancer. The important thing to note here is the risk of Vitamin D deficiency in doing so is also a potential problem which may end their career though not abruptly but insidiously and steadily [6]. In the experience of the primary researcher in educating the athletes on Vitamin D requirements there are lots of unanswered questions raised by the audience which needs to be attested by research. ...
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This is an Open Access Journal / article distributed under the terms of the Creative Commons Attribution License (CC BY-NC-ND 3.0) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. All rights reserved. The Vitamin D levels are most independent of many of the factors that were considered to be influencing the serum Vitamin D levels. This gave birth to a new ideology about the behaviour of the serum Vitamin D levels among different nationals. The present study was done to find the influence of "High Intensity Vigorous Exercise Protocol [HIVE-Protocol]" in the absorption of Vitamin D among Vitamin D deficient and insuffiient athletes from two districts of Kerala state. 73 subjects were randomized in to two groups, with 37 patients were allotted to group A and 36 to group B. 8 Sports Academies in the districts of Malappuram and Kozhikode (4 each) were taken into study. Routine Conventional Sports Specific Exercise Training Program are administered for both the groups and the Specially designed "High Intensity Vigorous Exercise Protocol [HIVE-Protocol] is administered to the group B alone. 25-Hydroxy Vitamin D levels and SF-12-Quality of life scale (SF-12-QOL) were used as outcome measures. The distribution of 25(OH) D between the groups didn't show any significant difference between the groups. The within group analysis of group A and group B shows significant difference between the pre-test values and post-test values for SF-12-PCS score, whereas SF-12-MCS values shows no significant difference in group A. Vitamin D values within group A and group B shows significant difference between the pre-test values and post-test values. Both group A intervention and group B intervention were effective in improving the quality of life and Vitamin D levels among athletes. Group B intervention ABSTRACT RESEARCH ARTICLE 34469 has a marginal advantage over group A in terms of improvement in 25-Hydroxy Vitamin D levels and mental health in quality of life.
... Moreover, the accumulation of ROS can cause damage to lipid membranes, a phenomenon known as lipid peroxidation, in which the deterioration of polyunsaturated fats occurs [157]. Vitamin E belongs to the non-enzymatic antioxidant defense system (Figure 4), whose main function is to interrupt lipid peroxidation reactions and remove free oxygen radicals, stabilizing cell membranes [158]. Because the antioxidant mechanisms implemented by the body are not always sufficient to counteract pro-oxidant events [159], some researchers have investigated the effects of possible vitamin E supplementation. ...
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Physical activity, combined with adequate nutrition, is considered a protective factor against cardiovascular disease, musculoskeletal disorders, and intestinal dysbiosis. Achieving optimal performance requires a significantly high energy expenditure, which must be correctly supplied to avoid the occurrence of diseases such as muscle injuries, oxidative stress, and heart pathologies, and a decrease in physical performance during competition. Moreover, in sports activities, the replenishment of water, vitamins, and minerals consumed during training is essential for safeguarding athletes’ health. In this scenario, vitamins play a pivotal role in numerous metabolic reactions and some muscle biochemical adaptation processes induced by sports activity. Vitamins are introduced to the diet because the human body is unable to produce these micronutrients. The aim of this review is to highlight the fundamental role of vitamin supplementation in physical activity. Above all, we focus on the roles of vitamins A, B6, D, E, and K in the prevention and treatment of cardiovascular disorders, muscle injuries, and regulation of the microbiome.
... In particular, vitamin D deficiency results in lower muscle strength, muscle mass, and muscle mass gain in response to training [29]. This is due to insufficient testosterone production in vitamin D deficiency [30]. Vitamin D deficiency is detected in athletes during the winter period in regions with insufficient solar activity [31], including Moscow (the place where this study was carried out). ...
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Background: Recent research indicates the prevalence of vitamin D deficiency worldwide and is conflicting evidence as to whether vitamin D supplementation actually improves physical performance. Objectives: The purpose of this study was to investigate the effect of vitamin D supplementation on improving muscle strength, muscle volume and cardiorespiratory fitness through resistance training in male athletes with vitamin D deficiency. Methods: This study was conducted with pre-test and post-test series design and quasi-experimental method. The population included 36 male futsal players with vitamin D deficiency that were randomly divided into four groups of nine: exercise (EX), exercise-supplement (EXS), supplement (SUP) and control (CON). SUP and EXS groups received vitamin D3 (50,000 intramuscular injections) every two weeks for 8 weeks and performed three resistance training (RT) sessions per week at a rate of 75% 1RM. Before and after intervention, blood sampling were drawn and measurements performed for 1RM, muscle volume (cm2), and VO2max by standard Bruce test. Correlated t-test was used to compare pre-test and post-test results and to measure the differences between groups, one-way analysis of variance and LSD post hoc test were used using SPSS statistical software. Results: Muscle volume increased significantly (P-value = 0.001) only in EX and EXS groups. Cardio-respiratory fitness did not change significantly in any of the groups (P > 0.05). There were no significant differences between EXS and SUP groups for any of the measured variables (P ≥ 0.05). Conclusions: It seems that simultaneous application of vitamin D supplementation and resistance training for 8 weeks does not have a significant effect on the improvement of the strength and endurance of futsal players.
Chapter
Vitamin D is a fat-soluble vitamin that plays a role in many functions in the body including musculoskeletal, immune, and neurological health. Vitamin D can be obtained through sun exposure, diet, and supplements; however, most Americans do not meet the recommended amount of vitamin D daily. Furthermore, the prevalence of vitamin D deficiency in the US is estimated to be around 40%. Athletes may be at an increased risk for vitamin D deficiency related to increased physical activity and enzymatic activity. Athletes with spinal cord injury (SCI) may be at even higher risk of vitamin D deficiency due to a lack of mobility, thermoregulatory dysfunction, and malabsorption concerns related to anticonvulsant medications. Athletes with SCI should be screened biannually for 25(OH)D status to determine whether supplementation is warranted. A 12- to 16-week sliding scale supplementation protocol based on the individual’s vitamin D status can be applied for individuals with an insufficient or deficient status. However, it remains unclear if there is a relationship between athletic performance and vitamin D status and there is a need for more research in this area.
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Vitamin D deficiency is now recognized as an epidemic in the United States. The major source of vitamin D for both children and adults is from sensible sun exposure. In the absence of sun exposure 1000 IU of cholecalciferol is required daily for both children and adults. Vitamin D deficiency causes poor mineralization of the collagen matrix in young children's bones leading to growth retardation and bone deformities known as rickets. In adults, vitamin D deficiency induces secondary hyperparathyroidism, which causes a loss of matrix and minerals, thus increasing the risk of osteoporosis and fractures. In addition, the poor mineralization of newly laid down bone matrix in adult bone results in the painful bone disease of osteomalacia. Vitamin D deficiency causes muscle weakness, increasing the risk of falling and fractures. Vitamin D deficiency also has other serious consequences on overall health and well-being. There is mounting scientific evidence that implicates vitamin D deficiency with an increased risk of type I diabetes, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and many common deadly cancers. Vigilance of one's vitamin D status by the yearly measurement of 25-hydroxyvitamin D should be part of an annual physical examination.
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Recent evidence suggests that vitamin D intakes above current recommendations may be associated with better health outcomes. However, optimal serum concentrations of 25-hydroxyvitamin D [25(OH)D] have not been defined. This review summarizes evidence from studies that evaluated thresholds for serum 25(OH)D concentrations in relation to bone mineral density (BMD), lower-extremity function, dental health, and risk of falls, fractures, and colorectal cancer. For all endpoints, the most advantageous serum concentrations of 25(OH)D begin at 75 nmol/L (30 ng/mL), and the best are between 90 and 100 nmol/L (36-40 ng/mL). In most persons, these concentrations could not be reached with the currently recommended intakes of 200 and 600 IU vitamin D/d for younger and older adults, respectively. A comparison of vitamin D intakes with achieved serum concentrations of 25(OH)D for the purpose of estimating optimal intakes led us to suggest that, for bone health in younger adults and all studied outcomes in older adults, an increase in the currently recommended intake of vitamin D is warranted. An intake for all adults of > or =1000 IU (25 microg) [DOSAGE ERROR CORRECTED] vitamin D (cholecalciferol)/d is needed to bring vitamin D concentrations in no less than 50% of the population up to 75 nmol/L. The implications of higher doses for the entire adult population should be addressed in future studies.
Conference Paper
Vitamin D deficiency is now recognized as an epidemic in the United States. The major source of vitamin D for both children and adults is from sensible sun exposure. In the absence of sun exposure 1000 IU of cholecalciferol is required daily for both children and adults. Vitamin D deficiency causes poor mineralization of the Collagen matrix in young children's bones leading to growth retardation and bone deformities known as rickets. In adults, vitamin D deficiency induces secondary hyperparathyroidism, which causes a loss of matrix and minerals, thus increasing the risk of osteoporosis and fractures. In addition, the poor mineralization of newly laid down bone matrix in adult bone results in the painful bone disease of osteomalacia. Vitamin D deficiency causes muscle weakness, increasing the risk of falling and fractures. Vitamin D deficiency also has other serious consequences on overall health and well-being. There is mounting scientific evidence that implicates vitamin D deficiency with an increased risk of type I diabetes, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and many common deadly cancers. Vigilance of one's vitamin D status by the yearly measurement of 25-hydroxyvitamin D should be part of an annual physical examination.