Vitamin D: The "sunshine" vitamin

Abstract

Vitamin D insufficiency affects almost 50% of the population worldwide. An estimated 1 billion people worldwide, across all ethnicities and age groups, have a vitamin D deficiency (VDD). This pandemic of hypovitaminosis D can mainly be attributed to lifestyle (for example, reduced outdoor activities) and environmental (for example, air pollution) factors that reduce exposure to sunlight, which is required for ultraviolet-B (UVB)-induced vitamin D production in the skin. High prevalence of vitamin D insufficiency is a particularly important public health issue because hypovitaminosis D is an independent risk factor for total mortality in the general population. Current studies suggest that we may need more vitamin D than presently recommended to prevent chronic disease. As the number of people with VDD continues to increase, the importance of this hormone in overall health and the prevention of chronic diseases are at the forefront of research. VDD is very common in all age groups. As few foods contain vitamin D, guidelines recommended supplementation at suggested daily intake and tolerable upper limit levels. It is also suggested to measure the serum 25-hydroxyvitamin D level as the initial diagnostic test in patients at risk for deficiency. Treatment with either vitamin D2 or vitamin D3 is recommended for deficient patients. A meta-analysis published in 2007 showed that vitamin D supplementation was associated with significantly reduced mortality. In this review, we will summarize the mechanisms that are presumed to underlie the relationship between vitamin D and understand its biology and clinical implications.

Full text

118 Journal of Pharmacology and Pharmacotherapeutics | April-June 2012 | Vol 3 | Issue 2
Vitamin D: The “sunshine” vitamin
Rathish Nair, Arun Maseeh
Medical Services Department, Torrent Pharmaceuticals Ltd., Ahmedabad, Gujarat, India
Review Article
Address for correspondence:
Rathish Nair, Medical Advisor, Torrent Pharmaceuticals Ltd., Near Dinesh Hall, Off. Ashram Road, Ahmedabad 380 009, Gujarat, India.
E-mail: drrathishnair@yahoo.co.in
ABSTRACT
Vitamin D insufciency affects almost 50% of the population worldwide. An estimated 1 billion people worldwide,
across all ethnicities and age groups, have a vitamin D deciency (VDD). This pandemic of hypovitaminosis D
can mainly be attributed to lifestyle (for example, reduced outdoor activities) and environmental (for example,
air pollution) factors that reduce exposure to sunlight, which is required for ultraviolet-B (UVB)-induced vitamin
D production in the skin. High prevalence of vitamin D insufciency is a particularly important public health
issue because hypovitaminosis D is an independent risk factor for total mortality in the general population.
Current studies suggest that we may need more vitamin D than presently recommended to prevent chronic
disease. As the number of people with VDD continues to increase, the importance of this hormone in overall
health and the prevention of chronic diseases are at the forefront of research. VDD is very common in all
age groups. As few foods contain vitamin D, guidelines recommended supplementation at suggested daily
intake and tolerable upper limit levels. It is also suggested to measure the serum 25-hydroxyvitamin D level
as the initial diagnostic test in patients at risk for deciency. Treatment with either vitamin D2 or vitamin D3 is
recommended for decient patients. A meta-analysis published in 2007 showed that vitamin D supplementation
was associated with signicantly reduced mortality. In this review, we will summarize the mechanisms that are
presumed to underlie the relationship between vitamin D and understand its biology and clinical implications.
Key words: Cancer, fat soluble vitamin, hypertension, obesity, vitamin D analogs
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DOI:
10.4103/0976-500X.95506
INTRODUCTION
Vitamin D insufciency affects almost 50% of the population
worldwide.[1] An estimated 1 billion people worldwide, across
all ethnicities and age groups, have a vitamin D deciency
(VDD).[1-3] This pandemic of hypovitaminosis D can mainly
be attributed to lifestyle and environmental factors that reduce
exposure to sunlight, which is required for ultraviolet-B
(UVB)-induced vitamin D production in the skin. Black people
absorb more UVB in the melanin of their skin than do white
people and, therefore, require more sun exposure to produce
the same amount of vitamin D.[4]
The high prevalence of vitamin D insufciency is a particularly
important public health issue because hypovitaminosis D is
an independent risk factor for total mortality in the general
population.[5] Emerging research supports the possible role
of vitamin D against cancer, heart disease, fractures and
falls, autoimmune diseases, inuenza, type-2 diabetes, and
depression. Many health care providers have increased their
recommendations for vitamin D supplementation to at least
1000 IU.[6] A meta-analysis published in 2007 showed that
vitamin D supplementation was associated with signicantly
reduced mortality.[7] In this review, we will focus on the biology
of vitamin D and summarize the mechanisms that are presumed
to underlie the relationship between vitamin D and its clinical
implications.
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Nair and Maseeh: Vitamin D: The “sunshine” vitamin
Journal of Pharmacology and Pharmacotherapeutics | April-June 2012 | Vol 3 | Issue 2 119
Biology of the sunshine vitamin
Vitamin D is unique because it can be made in the skin from
exposure to sunlight.[3,8-10] Vitamin D exists in two forms.
Vitamin D2 is obtained from the UV irradiation of the yeast
sterol ergosterol and is found naturally in sun-exposed
mushrooms. UVB light from the sun strikes the skin, and
humans synthesize vitamin D3, so it is the most “natural” form.
Human beings do not make vitamin D2, and most oil-rich sh
such as salmon, mackerel, and herring contain vitamin D3.
Vitamin D (D represents D2, or D3, or both) that is ingested is
incorporated into chylomicrons, which are absorbed into the
lymphatic system and enter the venous blood. Vitamin D that
comes from the skin or diet is biologically inert and requires its
rst hydroxylation in the liver by the vitamin D-25-hydroxylase
(25-OHase) to 25(OH)D.[3,11] However, 25(OH)D requires a
further hydroxylation in the kidneys by the 25(OH)D-1-OHase
(CYP27B1) to form the biologically active form of vitamin
D 1,25(OH)2D.[3,11] 1,25(OH)2D stimulates intestinal calcium
absorption.[12] Without vitamin D, only 10–15% of dietary
calcium and about 60% of phosphorus are absorbed. Vitamin
D sufciency enhances calcium and phosphorus absorption
by 30–40% and 80%, respectively.[3,13]
Vitamin D receptor (VDR) is present in most tissues and cells
in the body.[6,14] 1,25(OH)2D has a wide range of biological
actions, such as inhibition of cellular proliferation and
inducing terminal differentiation, inhibiting angiogenesis,
stimulating insulin production, inhibiting renin production,
and stimulating macrophage cathelicidin production.[6,14-16]
The local production of 1,25(OH)2D may be responsible for
regulating up to 200 genes[17] that may facilitate many of the
pleiotropic health benets that have been reported for vitamin
D.[3,8,9,14]
Vitamin D deciency: Prevalence
VDD has been historically dened and recently recommended
by the Institute of Medicine (IOM) as a 25(OH)D of less than
0.8 IU. Vitamin D insufciency has been dened as a 25(OH)
D of 21–29 ng/mL.[1,18-23] Children and young- and middle-
aged adults are at equally high risk for VDD and insufciency
worldwide. VDD is common in Australia, the Middle East,
India, Africa, and South America.[1,24,25] Pregnant and lactating
women who take a prenatal vitamin and a calcium supplement
with vitamin D remain at high risk for VDD.[26-28]
Vitamin D deciency, why it happens?
The major source of vitamin D for children and adults is
exposure to natural sunlight.[1,29-32] Thus, the major cause of
VDD is inadequate exposure to sunlight.[29,33-35] Wearing a
sunscreen with a sun protection factor of 30 reduces vitamin
D synthesis in the skin by more than 95%.[36] People with a
naturally dark skin tone have natural sun protection and require
at least three to ve times longer exposure to make the same
amount of vitamin D as a person with a white skin tone.[37,38]
There is an inverse association of serum 25(OH)D and body
mass index (BMI) greater than 30 kg/m2, and thus, obesity is
associated with VDD.[39]
Patients with one of the fat malabsorption syndromes
and bariatric patients are often unable to absorb the fat-
soluble vitamin D, and patients with nephritic syndrome
lose 25(OH)D bound to the vitamin D-binding protein
in the urine.[1] Patients on a wide variety of medications,
including anticonvulsants and medications to treat AIDS/
HIV, are at risk because these drugs enhance the catabolism
of 25(OH)D and 1,25(OH)2D.
[40] Patients with chronic
granuloma-forming disorders (sarcoidosis, tuberculosis, and
chronic fungal infections), some lymphomas, and primary
hyperparathyroidism who have increased metabolism of
25(OH)D to 1,25(OH)2D are also at high risk for VDD.[41,42]
Vitamin D deciency: Consequences
VDD results in abnormalities in calcium, phosphorus, and
bone metabolism. VDD causes a decrease in the absorption
of dietary calcium and phosphorus, resulting in an increase in
PTH levels.[1,3,18,43] The PTH-mediated increase in osteoclastic
activity creates local foci of bone weakness and causes
a generalized decrease in bone mineral density (BMD),
resulting in osteopenia and osteoporosis. An inadequate
calcium–phosphorus product causes a mineralization defect
in the skeleton.[1,44] In young children who have little mineral
in their skeleton, this defect results in a variety of skeletal
deformities classically known as rickets.[45,46] VDD also causes
muscle weakness; affected children have difculty in standing
and walking,[46,47] whereas the elderly have increasing sway
and more frequent falls,[48,49] thereby increasing their risk of
fracture.
Groups at risk of vitamin-D inadequacy
Obtaining sufcient vitamin D from natural food sources
alone is difcult. Consumption of vitamin D-fortied foods
and exposure to some sunlight are essential for maintaining
a healthy vitamin D status. Dietary supplements might be
required to meet the daily need for vitamin D in some group
of people.[50]
Breastfed infants
Vitamin D requirements cannot ordinarily be met by human
milk alone,[23,51] which provides <25 IU/L to 78 IU/L.[52]
Vitamin D content of human milk is related to the mother’s
vitamin D status; therefore mothers who supplement with
high doses of vitamin D may have high levels of vitamin
D in their milk.[52] American Association of Paediatricians
(AAP) recommends that exclusively and partially breastfed
infants must be supplemented with 400 IU of vitamin D per
day,[52,53] the recommended daily allowance for this nutrient
during infancy.
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120 Journal of Pharmacology and Pharmacotherapeutics | April-June 2012 | Vol 3 | Issue 2
Older adults
Older adults are at high risk of developing vitamin D
insufciency because of aging. Their skin cannot synthesize
vitamin D as efficiently, they are likely to spend more
time indoors, and they may have inadequate intakes of the
vitamin.
[23]
People with limited sun exposure
Homebound individuals, women who wear long robes and head
coverings for religious reasons, and people with occupations
that limit sun exposure are unlikely to obtain adequate
vitamin D from sunlight.[54,55] The signicance of the role that
sunscreen may play in reducing vitamin D synthesis is still
unclear.
[23] Intake of RDA levels of vitamin D from foods and/
or supplements will provide adequate amounts of this nutrient
to these individuals.
People with dark skin
Larger amounts of the pigment melanin in the epidermal layer
result in darker skin and reduce the skin’s ability to produce
vitamin D from sunlight.[23] It is not sure that lower levels of
25(OH)D for persons with dark skin have signicant health
consequences. Intake of RDA levels of vitamin D from foods
and/or supplements will provide adequate amounts of this
nutrient to these individuals.
People with fat malabsorption
Vitamin D is fat soluble, therefore it requires some dietary fat
in the gut for absorption. Individuals with reduced ability to
absorb dietary fat might require vitamin D supplements.
[56]
Fat malabsorption is associated with a variety of medical
conditions including some forms of liver disease, cystic
brosis, and Crohn’s disease.[57]
People who are obese or who have undergone
gastric bypass surgery
A BMI value of ≥30 is associated with lower serum 25(OH)
D levels compared with nonobese individuals. Obese people
may need larger than usual intakes of vitamin D to achieve
25(OH)D levels comparable to those of normal weight.[23]
Greater amounts of subcutaneous fat sequester (captivate)
more of the vitamin and alter its release into the circulation.
Individuals who have undergone gastric bypass surgery may
become vitamin D decient over time without a sufcient
intake of vitamin D from food or supplements; moreover part
of the upper small intestine where vitamin D is absorbed is
bypassed.[58,59]
Sources of vitamin D
A major source of vitamin D for most humans is synthesized
from the exposure of the skin to sunlight typically between
1000 h and 1500 h in the spring, summer, and fall.[1,29,33,60]
Vitamin D produced in the skin may last at least twice as long in
the blood compared with ingested vitamin D.[61] When an adult
wearing a bathing suit is exposed to one minimal erythemal
dose of UV radiation (a slight pinkness to the skin 24 h after
exposure), the amount of vitamin D produced is equivalent
to ingesting between 10,000 and 25,000 IU.[33] A variety of
factors reduce the skin’s production of vitamin D3, including
increased skin pigmentation, aging, and the topical application
of a sunscreen.[1,36,37] An alteration in the zenith angle of the sun
caused by a change in latitude, season of the year, or time of day
dramatically inuences the skin’s production of vitamin D3.[1,33]
Physiological actions of vitamin D
Vitamin D is a fat-soluble vitamin that acts as a steroid
hormone. In humans, the primary source of vitamin D is UVB-
induced conversion of 7-dehydrocholesterol to vitamin D in the
skin [Figure 1].[1,62] Vitamin D inuences the bones, intestines,
immune and cardiovascular systems, pancreas, muscles, brain,
and the control of cell cycles.[63]
Vitamin D undergoes two hydroxylations in the body for
activation. Calcitriol (1,25-dihydroxyvitamin D3), the active
form of vitamin D, has a half-life of about 15 h, while calcidiol
(25-hydroxyvitamin D3) has a half-life of about 15 days.[63]
Vitamin D binds to receptors located throughout the body.
25(OH)D is transformed by renal or extrarenal 1α-hydroxylase
into 1,25-dihydroxyvitamin D (1,25[OH]2D), which circulates
at much lower serum concentrations than 25(OH)D, but
has a much higher affinity to the VDR.[64] Studies have,
however, shown that many other cell types, including those
of the vascular wall, express 1α-hydroxylase with subsequent
intracellular conversion of 25(OH)D to 1,25(OH)2D, which
exerts its effects at the level of the individual cell or tissue
before being catabolized to biologically inactive calcitroic
acid.[1,65,66] Factors such as broblast growth factor 23 and
Klotho, which suppress 1α-hydroxylase expression, have
also been shown to regulate the renal conversion of 25(OH)
D to 1,25(OH)2D.[67] Importantly, extrarenal 1α-hydroxylase
expression also underlies various regulatory mechanisms.
In this context, extrarenal 1,25(OH)2D productions in
macrophages are stimulated by Toll-like receptor as part of
the innate immune response against intracellular bacteria.[68]
Another example of extrarenal regulation of 1α-hydroxylase is
that the increased production of 1,25(OH)2D by keratinocytes
in wounds[69] therefore provides a good estimate of vitamin D
status, but regulation of 1α-hydroxylase activity should also
be considered. Vitamin D crosses the blood–brain barrier and
the receptors for vitamin D are found across the brain, but its
precise role is still not known.
Drug interactions
Vitamin D supplements may interact with several types of
medications. Corticosteroids can reduce calcium absorption,
which results in impaired vitamin D metabolism.[9] Since
vitamin D is fat soluble, Orlistat and Cholestyramine can
reduce its absorption and should be taken several hours
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Nair and Maseeh: Vitamin D: The “sunshine” vitamin
Journal of Pharmacology and Pharmacotherapeutics | April-June 2012 | Vol 3 | Issue 2 121
apart from it.[9] Phenobarbital and phenytoin increase the
hepatic metabolism of vitamin D to inactive compounds and
decrease calcium absorption, which also impairs vitamin D
metabolism.
[9]
Dosing
Only a few foods are a good source of vitamin D. The best
way to get additional vitamin D is through supplementation.
Traditional multivitamins contain about 400 IU of vitamin D,
but many multivitamins now contain 800 to 1000 IU. A variety
of options are available for individual vitamin D supplements,
including capsules, chewable tablets, liquids, and drops. Cod
liver oil is a good source of vitamin D, but in large doses there
is a risk of vitamin A toxicity.[70]
Clinical benets of vitamin D
Cancer
Vitamin D decreases cell proliferation and increases cell
differentiation, stops the growth of new blood vessels, and
has signicant anti-inammatory effects.[71,72] Many studies
have suggested a link between low vitamin D levels and
an increased risk of cancer, with the strongest evidence for
colorectal cancer. In the Health Professionals Follow-up Study
(HPFS), subjects with high vitamin D concentrations were
half as likely to be diagnosed with colon cancer as those with
low concentrations.[71] A denitive conclusion cannot yet be
made about the association between vitamin D concentration
and cancer risk, but results from many studies are promising.
There is some evidence linking higher vitamin D intake to a
lower risk for breast cancer.[72] The effect of menopausal status
on this association is still unclear.
Heart disease
Several studies are providing evidence that the protective effect
of vitamin D on the heart could be via the renin–angiotensin
hormone system, through the suppression of inammation,
or directly on the cells of the heart and blood-vessel walls.[17]
In the Framingham Heart Study, patients with low vitamin D
concentrations (<15 ng/mL) had a 60% higher risk of heart
disease than those with higher concentrations.[17] In another
study, which followed men and women for 4 years, patients
with low vitamin D concentrations (<15 ng/mL) were three
times more likely to be diagnosed with hypertension than those
with high concentrations (>30 ng/mL).[73]
Hypertension
The third National Health and Nutrition Examination
Survey (NHANES-III),[74] which is representative of the
noninstitutionalized US civilian population, showed that
systolic blood pressure and pulse pressure were inversely
7 – dehydrocholesterol
(Vitamin D precursor of skin)
Previtamin D3
Cholecalciferol
(
D3
)
Foods and Su
pp
lements
25-h
y
drox
y
vitamin D3
Biologic Acons
1, 25-dihydroxyvitamin D3
(acvated form)
Ergocalciferol
Ultraviolet B (UVB) rays from Sun exposure
1-alpha-hydroxylase in kidneys
25 hydroxylase in liver
Binding to Vitamin D receptors
Figure 1: Vitamin D synthesis
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and signicantly correlated with 25(OH)D levels among
12,644 participants. Age-associated increase in systolic blood
pressure was signicantly lower in individuals with vitamin
D sufciency.[75,76] The prevalence of arterial hypertension
was also associated with reduced serum 25(OH)D levels
in 4030 participants of the German National Interview and
Examination Survey,[77] in 6810 participants of the 1958
British Birth Cohort,[78] and in other study populations.[79-87]
The antihypertensive effects of vitamin D are mediated by
renoprotective effects, suppression of the RAAS, by benecial
effects on calcium homeostasis, including the prevention of
secondary hyperparathyroidism, and by vasculoprotection.[85]
Obesity
Low concentrations of circulating vitamin D are common with
obesity and may represent a potential mechanism explaining
the elevated risk of certain cancers and cardiovascular
outcomes. Levels of 25(OH)D are inversely associated with
BMI, waist circumference, and body fat but are positively
associated with age, lean body mass, and vitamin D intake.
The prevalence of VDD is higher in black versus white
children regardless of season predictors of VDD in children
include black race, female sex, pre-pubertal status, and winter/
spring season.[88] Weight loss is associated with an increase in
25(OH)D levels among postmenopausal overweight or obese
women.[89]
Type 2 diabetes
A trial of nondiabetic patients aged 65 years and older found
that those who received 700 IU of vitamin D (plus calcium)
had a smaller rise in fasting plasma glucose over 3 years versus
those who received placebo.[90] A correlation between vitamin
D and the risk diabetes can be ruled in from the results.
Depression
A Norwegian trial of overweight subjects showed that those
receiving a high dose of vitamin D (20,000 or 40,000 IU
weekly) had a signicant improvement in depressive symptom
scale scores after 1 year versus those receiving placebo.[91] The
result determines a correlation between vitamin D and the risk
of depression.
Cognitive impairment
In the Invecchiare in Chianti (InCHIANTI) Italian population-
based study, low levels of vitamin D were associated with
substantial cognitive decline in the elderly population studied
during a 6-year period.[92] Low levels of 25(OH)D may be
especially harmful to executive functions, whereas memory
and other cognitive domains may be relatively preserved.
Parkinson’s disease
Parkinson’s disease is a major cause of disability in the
elderly population. Unfortunately, risk factors for this disease
are relatively unknown. Recently, it has been suggested that
chronically inadequate vitamin D intake may play a signicant
role in the pathogenesis of Parkinson’s disease. A cohort
study based on the Mini-Finland Health Survey demonstrated
that low vitamin D levels may predict the development of
Parkinson’s disease.[93]
Fractures and falls
Vitamin D is known to help the body absorb calcium,
and it plays a role in bone health. In addition, VDRs are
located on the fast-twitch muscle bers, which are the rst
to respond in a fall.[94] It is theorized that vitamin D may
increase muscle strength, thereby preventing falls.[6] Many
studies have shown an association between low vitamin D
concentrations and an increased risk of fractures and falls
in older adults.
A combined analysis of 12 fracture-prevention trials found
that supplementation with about 800 IU of vitamin D per
day reduced hip and nonspinal fractures by about 20%, and
that supplementation with about 400 IU per day showed no
benet.
[95] Researchers at the Jean Mayer USDA Human
Nutrition Research Center on Aging at Tufts University have
examined the best trials of vitamin D versus placebo for falls.
Their conclusion is that “fall risk reduction begins at 700 IU
and increases progressively with higher doses.”[94]
Autoimmune diseases
VDD can contribute to autoimmune diseases such as multiple
sclerosis (MS), type 1 diabetes, rheumatoid arthritis, and
autoimmune thyroid disease.[96]
A prospective study of white subjects found that those with
the highest vitamin D concentrations had a 62% lower risk of
developing MS versus those with the lowest concentrations.
[97]
A Finnish study that followed children from birth noted that
those given vitamin D supplements during infancy had a nearly
90% lower risk of developing type 1 diabetes compared with
children who did not receive supplements.[98]
Inuenza
VDD in the winter months may be the seasonal stimulus that
triggers inuenza outbreaks in the winter.[96] In a Japanese
randomized, controlled trial, children given a daily vitamin D
supplement of 1200 IU had a 40% lower rate of inuenza type
A compared with those given placebo; there was no signicant
difference in rates of inuenza type B.[99]
Bacterial vaginosis
An analysis of data from the National Health and Nutrition
Examination Survey showed that in pregnant women, VDD
was associated with nearly a 3-fold increased risk for Bacterial
Vaginosis (BV).[100] In non-pregnant women, VDD modulated
the association between smoking and BV.
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Pelvic oor disorders
The frequency of Pelvic oor disorders, including urinary
and fecal incontinence, is increasing with age. Pelvic oor
disorders have been linked to osteoporosis and low BMD and
remain one of the most common reasons for gynaecologic
surgery, with a failure rate of 30%. Subnormal levels of
25(OH)D are common among women, and lower levels
are associated with a higher likelihood of pelvic floor
disorders.[101] Results from the National Health and Nutrition
Examination Survey conrmed that lower 25(OH) D levels
are associated with a greater risk for urinary incontinence in
women older than 50 years.
Age-related macular regeneration
High vitamin D blood levels appear to be associated with a
decreased risk for the development of early age-related macular
degeneration (AMD) among women younger than 75 years.
[102]
Among women younger than 75 years, there is a lower risk
for early AMD with higher vitamin D levels, with a threshold
effect at 15.22 ng/L serum 25 (OH)D.
RECOMMENDATION GUIDELINES:
ENDOCRINE SOCIETY OF CLINICAL
PRACTICE
Diagnostic procedure
ESCP recommend screening for VDD in individuals at risk
for deciency and not for patients who are not at risk. Serum
circulating 25-hydroxyvitamin D [25(OH) D] level should be
measured to evaluate vitamin D status in patients who are at
risk for VDD. VDD is dened as a 25(OH) D below 20 ng/
mL (50 nmol/L).[103]
Recommended dietary intakes of vitamin D
ESCP suggests that obese children and adults on anticonvulsant
medications, glucocorticoids, antifungals such as ketoconazole,
and medications for AIDS should be given at least two to three
times more vitamin D for their age group to satisfy their body’s
vitamin D requirement.
ESCP suggests that the maintenance tolerable upper limits
(UL) of vitamin D, which is not to be exceeded without
medical supervision, should be 1000 IU/d for infants up to
6 months, 1500 IU/d for infants from 6 months to 1 year,
at least 2500 IU/d for children aged 1–3 years, 3000 IU/d
for children aged 4–8 years, and 4000 IU/d for everyone
over 8 years. Higher levels of 2000 IU/d for children 0–1
year, 4000 IU/d for children 1–18 years, and 10000 IU/d
for children and adults 19 years and older may be needed
to correct VDD.[103]
Treatment and prevention strategies
Vitamin D2 or vitamin D3 can be used for the treatment and
prevention of VDD [Table 2]. In patients with extrarenal
production of 1,25(OH)2D, serial monitoring of 25(OH)
D levels and serum calcium levels during treatment with
vitamin D to prevent hypercalcemia is suggested [Table 2].
Primary hyperparathyroidism and VDD need treatment with
vitamin D.[103]
Noncalcemic benets of vitamin D
ESCP recommends prescribing vitamin D supplementation
for fall prevention and do not recommend supplementation
beyond recommended daily needs for the purpose of
preventing cardiovascular disease or death or improving
quality of life.[103]
Table 2: Treatment and prevention strategies[103]
Patient prole Age group Dose
Infants and toddlers 0–1 year • 2000 IU/d for 6 weeks or 50,000 IU once weekly for 6 weeks to achieve
blood level 25 (OH) D above 30 ng/mL
• Followed by maintenance therapy of 400–1000 IU/d
Children 1–18 years • 2000 IU/d for at least 6 weeks or with 50,000 IU for once a week to
achieve blood level 25 (OH) D above 30 ng/mL
• Followed by maintenance therapy of 400–1000 IU/d
Adults 18 years and above • 50,000 IU once a week for 8 weeks or its equivalent of 6000 IU/d for 8
weeks to achieve blood level 25 (OH) D above 30 ng/mL
• Followed by maintenance therapy of 1500–2000 IU/d
Patients with obesity/ malabsorption
syndromes/on medications affecting
vitamin D metabolism
• 6000–10,000 IU/d to maintain a 25 (OH) D level above 30 ng/mL
• Followed by maintenance therapy of 3000–6000 IU/d
Table 1: Recommended dietary intakes of vitamin D for patients at risk for vitamin D deciency[103]
Patient prole Age group Dose
Infants and children 0–1 year 1000 IU/d required to raise the blood level consistently above 30 ng/mL
Children 1 year and older 1000 IU/d required to raise the blood level consistently above 30 ng/mL
Adults 19–50 years 1500–2000 IU/d required to raise the blood level consistently above 30 ng/mL
Elderly 50–70 year and 70+ year 1500–2000 IU/d required to raise the blood level consistently above 30 ng/mL
Pregnant and lactating women – 1500–2000 IU/d required to raise the blood level consistently above 30 ng/mL
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124 Journal of Pharmacology and Pharmacotherapeutics | April-June 2012 | Vol 3 | Issue 2
Vitamin D analogs
Vitamin D has ve natural analogs, called vitamers, and four
synthetic analogs which are made synthetically. Vitamin D
analogs are chemically classied as secosteroids, which are
steroids with one broken bond.
Natural analogs of vitamin D
• Vitamin D1 is a molecular compound of ergocalciferol (D2)
with lumisterol in a 1:1 ratio.
• Vitamin D2 (ergocalciferol) is produced by invertebrates,
some plants, and fungi. Biological production of D2 is
stimulated by ultraviolet light.
• Vitamin D3 (cholecalciferol) is synthesized in the skin by
the reaction of 7-dehydrocholesterol with UVB radiation,
present in sunlight with an UV index of three or more.
• Vitamin D4 is an analog scientifically known as
22-dihydroergocalciferol.
• Vitamin D5 (sitocalciferol) is an analog created from
7-dehydrositosterol.
Synthetic analogs of vitamin D
• Maxacalcitol (22-oxacalcitriol or OCT) is the first
analog found to have a wider therapeutic window than
1,25(OH)2D3.[104]
• Calcipotriol is derived from calcitriol was rst discovered
during trials involving the use of vitamin D for treating
osteoporosis.
• Dihydrotachysterol (DHT) is a synthetic form of vitamin
D that many consider superior to natural D2 and D3. It
becomes active by the liver without needing to go through
hydroxylation in the kidneys.
• Paricalcitol (19-norD2) is also derived from calcitriol. It is
the rst of the new vitamin D analogs to be approved for
secondary hyperparathyroidism and differs from calcitriol
in that it lacks the exocyclic carbon 19 and has a vitamin
D2 side chain instead of a vitamin D3 side chain.[105]
• Tacalcitol is a derivative of vitamin D3. It is known to hinder
keratinocytes in the skin.
• Doxercalciferol (1α(OH)D2) is a prodrug and must be
activated in vivo. It is less toxic than 1α (OH)D3
[106] when
administered chronically.
• Falecalcitriol (1,25(OH) 2-26, 27-F6-D3) is approved for
secondary hyperparathyroidism in Japan.[105] It is more
active than calcitriol because of its slower metabolism.[107]
CONCLUSION
Numbers of people with VDD are continuously increasing; the
importance of this hormone in overall health and the prevention
of chronic diseases are at the forefront of research. VDD is very
common in all age groups. Very few foods contain vitamin D
therefore guidelines recommended supplementation of vitamin
D at tolerable UL levels. It is also suggested to measure the
serum 25-hydroxyvitamin D level as the initial diagnostic test
in patients at risk for deciency. Treatment with either vitamin
D2 or vitamin D3 is recommended for the decient patients.
More research is required to recommend screening individuals
who are not at risk for deciency or to prescribe vitamin D to
attain the noncalcemic benet for cardiovascular protection.
ACKNOWLEDGMENTS
We would like to acknowledge Mr. Anand Iyer, VP, Marketing
and Sales, Torrent Pharmaceuticals Ltd., for providing us moral
and infrastructural support for drafting this scientic review and
Mr. Ramesh Jayswal, Executive—Information Science, Torrent
Pharmaceuticals Ltd., who has enabled us with the required reference
articles and scientic inputs to draft this review article.
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How to cite this article: Nair R, Maseeh A. Vitamin D: The "sunshine" vitamin.
J Pharmacol Pharmacother 2012;3:118-26.
Source of Support: Nil, Conict of Interest: None declared.
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