Effect of Vitamin D Supplementation on Testosterone Levels in Men

Abstract

The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men. We therefore aimed to evaluate whether vitamin D supplementation influences testosterone levels in men. Healthy overweight men undergoing a weight reduction program who participated in a randomized controlled trial were analyzed for testosterone levels. The entire study included 200 nondiabetic subjects, of whom 165 participants (54 men) completed the trial. Participants received either 83 μg (3,332 IU) vitamin D daily for 1 year (n = 31) or placebo (n =2 3). Initial 25(OH)D concentrations were in the deficiency range (< 50 nmol/l) and testosterone values were at the lower end of the reference range (9.09-55.28 nmol/l for males aged 20-49 years) in both groups. Mean circulating 25(OH)D concentrations increased significantly by 53.5 nmol/l in the vitamin D group, but remained almost constant in the placebo group. Compared to baseline values, a significant increase in total testosterone levels (from 10.7 ± 3.9 nmol/l to 13.4 ± 4.7 nmol/l; p < 0.001), bioactive testosterone (from 5.21 ± 1.87 nmol/l to 6.25 ± 2.01 nmol/l; p = 0.001), and free testosterone levels (from 0.222 ± 0.080 nmol/l to 0.267 ± 0.087 nmol/l; p = 0.001) were observed in the vitamin D supplemented group. By contrast, there was no significant change in any testosterone measure in the placebo group. Our results suggest that vitamin D supplementation might increase testosterone levels. Further randomized controlled trials are warranted to confirm this hypothesis.

Full text

Short Communication
Pilz S et al. Vitamin D and Testosterone … Horm Metab Res
received 04.08.2010
accepted 03.11.2010
Bibliography
DOI http://dx.doi.org/
10.1055/s-0030-1269854
Published online: 2010
Horm Metab Res
© Georg Thieme Verlag KG
Stuttgart · New York
ISSN 0018-5043
Correspondence
A. Zittermann
Clinic for Thoracic and Cardio-
vascular Surgery
Heart Centre North Rhine-
Westfalia
Ruhr University Bochum
Georgstra ß e 11
32545 Bad Oeynhausen
Germany
Tel.: + 49 / 5731 / 97 1912
Fax: + 49 / 5731 / 97 2020
azittermann@hdz-nrw.de
Eff ect of Vitamin D Supplementation on Testosterone
Levels in Men
[2, 3] . These results are of particular interest
because both, vitamin D defi ciency and hypogo-
nadism are associated with skeletal diseases (e. g.,
osteoporosis or muscle weakness) as well as
extra-skeletal disorders (e. g., cardiovascular dis-
ease or obesity) [1, 4, 5] . Recently, some of us [6]
have shown in 2 299 men referred for coronary
angiography that 25-hydroxyvitamin D [25(OH)D]
levels are signifi cantly associated with testoster-
one levels and that both hormones reveal similar
seasonal variations with a peak at the end of
summer. Whether there exists a causal link
between vitamin D and testosterone status is,
however, currently not known. Therefore, a sub-
group analysis of a previously published prospec-
tive, randomized vitamin D supplementation
trial was performed in overweight subjects [7] .
Here, we present results on serum testosterone
concentrations in the male participants of this
study.
Introduction
▼
Vitamin D defi ciency is currently considered an
important public health problem being associ-
ated with musculoskeletal diseases, cardiovascu-
lar disease, cancer, and infectious and
autoimmune diseases [1] . The vitamin D receptor
(VDR), as well as key enzymes for vitamin D
metabolism, are widely expressed in human tis-
sues and cells [2] . In this context, Blomberg
Jensen et al. [3] observed signifi cant expressions
of the VDR and vitamin D metabolizing enzymes
in the male reproductive tract including Leydig
cells of the testis. These data raised the question
whether vitamin D is able to infl uence male
reproductive hormone production. The existence
of such an eff ect is supported by previous studies
suggesting that vitamin D defi ciency may con-
tribute to reduced fertility and hypogonadism
Authors S. Pilz
1
, *
, S. Frisch
2
, * , H. Koertke
2 , J. Kuhn
3 , J. Dreier
3 , B. Obermayer-Pietsch
1 , E. Wehr
1 , A. Zittermann
2
Affi liations 1 Department of Internal Medicine, Division of Endocrinology and Metabolism, Medical University of Graz, Austria
2 Clinic for Thoracic and Cardiovascular Surgery, Heart Centre North Rhine-Westphalia, Ruhr University Bochum,
Bad Oeynhausen, Germany
3 Institute for Laboratory and Transfusion Medicine, Heart Centre North Rhine-Westphalia, Ruhr University Bochum,
Bad Oeynhausen, Germany
Abstract
▼
The male reproductive tract has been identifi ed
as a target tissue for vitamin D, and previous data
suggest an association of 25-hydroxy vitamin D
[25(OH)D] with testosterone levels in men. We
therefore aimed to evaluate whether vitamin D
supplementation infl uences testosterone levels
in men. Healthy overweight men undergoing a
weight reduction program who participated in
a randomized controlled trial were analyzed for
testosterone levels. The entire study included
200 nondiabetic subjects, of whom 165 par-
ticipants (54 men) completed the trial. Partici-
pants received either 83 μ g (3 332 IU) vitamin D
daily for 1 year (n = 31) or placebo (n = 23). Initial
25(OH)D concentrations were in the defi ciency
range ( < 50 nmol / l) and testosterone values
were at the lower end of the reference range
(9.09 – 55.28 nmol / l for males aged 20 – 49 years)
in both groups. Mean circulating 25(OH)D con-
centrations increased signifi cantly by 53.5 nmol / l
in the vitamin D group, but remained almost
constant in the placebo group. Compared to
baseline values, a signifi cant increase in total
testosterone levels (from 10.7 ± 3.9 nmol / l to
13.4 ± 4.7 nmol / l; p < 0.001), bioactive testoster-
one (from 5.21 ± 1.87 nmol / l to 6.25 ± 2.01 nmol / l;
p = 0.001), and free testosterone levels (from
0.222 ± 0.080 nmol / l to 0.267 ± 0.087 nmol / l;
p = 0.001) were observed in the vitamin D supple-
mented group. By contrast, there was no signifi -
cant change in any testosterone measure in the
placebo group. Our results suggest that vitamin
D supplementation might increase testosterone
levels. Further randomized controlled trials are
warranted to confi rm this hypothesis.
* Both authors contributed equally to the present work.
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Short Communication
Pilz S et al. Vitamin D and Testosterone … Horm Metab Res
Subjects and Methods
▼
Study subjects were derived from a weight reduction program
over 12 months, which included a daily supplementation of
either 83 μ g (3 332 IU) vitamin D or placebo as part of a double-
blind randomized controlled trial [7] . Details on the study design
and major outcomes of the trial have been published previously
[7] . Out of 200 nondiabetic individuals (62 men) who were
included in the study, 165 (54 men) completed the trial. Only
male study subjects were analyzed for the present work. The
number of dropouts (3 men in the placebo and 5 men in the
vitamin D group) did not diff er signifi cantly between groups
(p = 0.745). The original study was registered at clinical trials.gov
as NCT004493012.
Participants were continuously recruited from December 2005
to October 2006 throughout the year. Fasting blood samples
were drawn at study begin and after 1 year. Specimens were
centrifuged at room temperature. Thereafter, serum aliquots
were stored at − 80 ° C until analyses. To avoid inter-assay varia-
tions, the samples of each participant were analyzed within the
same assay run. Concentrations of 25(OH)D were determined by
means of a radioimmunoassay (DiaSorin, Stillwater, MN, USA)
with an intra-assay CV of < 7 % . According to Holick [1] , vitamin
D defi ciency is defi ned as a 25(OH)D level of less than 50 nmol / l,
whereas a level of 52.5 – 72.5 nmol / l indicates a relative insuffi -
ciency, and a level of 75 nmol / l or greater indicates suffi cient
vitamin D. The serum concentrations of 1,25-dihydroxyvitamin
D [1, 25(OH) 2
D] were measured by a test kit provided by Immun-
diagnostik (Bensheim, Germany). The serum levels of parathy-
roid hormone (PTH), total testosterone (TT), and sex hormone
binding globulin (SHBG) were analyzed by using the Immulite
2000 system (Siemens, Munich, Germany). The reference range
for total testosterone is 9.09 – 55.28 nmol / l for males aged 20 – 49
years and 6.28 – 26.30 nmol / l for males aged ≥ 50 years. The SHBG
reference range for males is 13 – 71 nmol / l. The within-run and
total coeffi cients of variation for SHBG and testosterone are 2.5 %
and 5.2 % , respectively. Serum albumin was measured by using
the Architect autoanalyzer (Abbott, Wiesbaden, Germany). Bio-
active testosterone (BAT; reference range: 2.14 – 13.60 nmol / l)
and free testosterone (fT; reference range: 0.090 – 0.580 nmol / l)
were calculated according to Vermeulen et al. [8] .
Baseline characteristics stratifi ed by treatment group (vitamin D
vs. placebo) are presented as means ± SD for continuous varia-
bles. Intra-group comparisons (paired t -test) rather than inter-
group comparisons were used at the end of the study because no
sex-stratifi ed randomization at baseline was performed. Statisti-
cal analyses were performed by SPSS 16.0 (SPSS Inc, Chicago,
USA) and a p-value below 0.05 was considered statistically
signifi cant.
Results
▼
Baseline characteristics of the 54 male patients who completed
the trial are shown in ● ▶ Table 1 . At study entry, mean 25(OH)D
concentrations were in the defi ciency range in both groups. Dur-
ing follow-up, weight loss was 5.9 ± 5.3 kg (p < 0.001) in the vita-
min D group and 6.6 ± 5.7 kg in the placebo group (p < 0.001), and
thus similar in both groups. Circulating 25(OH)D increased by
53.5 ± 65.3 nmol / l to 86.4 ± 68.8 nmol / l in the vitamin D group
(p < 0.001), but increased only nonsignifi cantly in the placebo
group (increase by 5.8 ± 21.3 nmol / l to 35.5 ± 18.0 nmol / l;
p = 0.215). PTH decreased in the placebo and vitamin D group
(decrease by 0.94 ± 3.09; p = 0.035, and 0.60 ± 1.67; p = 0.040,
respectively), whereas 1,25(OH)
2 D tended to increase in both
groups (increase by 20.4 ± 41.0; p = 0.027 and 21.7 ± 106.0;
p = 0.100, respectively). At baseline, mean testosterone values
were at the lower end of the reference range in both groups. By
comparing baseline testosterone values with follow-up values in
the placebo group no signifi cant change in TT (11.8 ± 4.0 nmol / l
vs. 12.7 ± 5.45 nmol / l, p = 0.355), BAT (6.39 ± 2.22 nmol / l vs.
6.59 ± 2.33 nmol / l, p = 0.626) or fT (0.264 ± 0.087 nmol / l vs.
0.278 ± 0.097 nmol / l, p = 0.532) was found. In the vitamin D
group, however, a signifi cant increase in all measures of testos-
terone status was observed. TT increased from 10.7 ± 3.9 nmol / l
to 13.4 ± 4.7 nmol / l (p < 0.001), BAT from 5.21 ± 1.87 nmol / l to
6.25 ± 2.01 nmol / l (p = 0.001) and fT from 0.222 ± 0.080 nmol / l to
0.267 ± 0.087 nmol / l (p = 0.001). In the placebo group, there were
nonsignifi cant trends for seasonal diff erences in 25(OH)D and
testosterone values. Compared with men recruited in the sum-
mer half-year (mid April to mid October; n = 12), men recruited
in the winter half-year (mid October to mid April; n = 11) had
lower values of 25(OH)D (21.8 ± 9.8 nmol / l vs. 37.4 ± 30.0 nmol / l;
Table 1 Characteristics of the study groups at baseline and at the end of the study
Parameter Placebo group Vitamin D group p-Value
Baseline Study end Baseline Study end 2 vs. 4 2 vs. 3 4 vs. 5
Number 23 31 – – –
Age (years) 46.8 ± 12.0 49.4 ± 10.2 0.387 – –
Smokers ( % ) 56.5 38.7 0.271 – –
Alcohol (g / d) 20.0 ± 19.5 14.1 ± 15.3 17.7 ± 15.1 15.3 ± 13.8 0.646 0.138 0.703
25(OH)D (nmol / l) 29.7 ± 23.7 35.5 ± 8.1 32.5 ± 20.0 86.4 ± 68.8 0.659 0.215 < 0.001
1,25(OH) 2 D (pmol / l) 77.0 ± 25.9 97.4 ± 32.9 96.0 ± 39.6 127.7 ± 94.3 0.053 0.027 0.100
PTH (pmol / l) 5.07 ± 3.63 4.13 ± 1.48 4.14 ± 1.98 3.54 ± 1.76 0.237 0.035 0.040
Body weight (kg) 105.7 ± 14.3 99.0 ± 13.5 109.9 ± 16.1 104.0 ± 17.2 0.323 < 0.001 < 0.001
BMI (kg / m 2 ) 32.5 ± 3.8 30.5 ± 4.1 33.1 ± 3.9 31.2 ± 3.9 0.609 < 0.001 < 0.001
Albumin (mmol / l) 386 ± 182 302 ± 125 377 ± 194 297 ± 186 0.087 0.210 0.896
SHBG (mmol / l) 26.3 ± 13.7 29.5 ± 17.3 31.0 ± 10.3 35.3 ± 13.6 0.153 0.046 0.002
TT (nmol / l) 11.8 ± 4.0 12.7 ± 5.5 10.7 ± 3.9 13.4 ± 4.7 0.317 0.355 < 0.001
BAT (nmol / l) 6.39 ± 2.22 6.59 ± 2.33 5.21 ± 1.87 6.25 ± 2.01 0.040 0.626 0.001
fT (nmol / l) 0.264 ± 0.087 0.278 ± 0.097 0.222 ± 0.080 0.267 ± 0.087 0.067 0.532 0.001
Data are shown as means ± SD. Inter-group comparisons were performed by unpaired t -test and intra-group comparisons by paired t -test
25(OH)D: 25-hydroxyvitamin D; 1,25(OH) 2 D: 1,25-dihydroxyvitamin D; PTH: parathyroid hormone; BMI: body mass index; SHBG: sex-hormone binding
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Short Communication
Pilz S et al. Vitamin D and Testosterone … Horm Metab Res
p = 0.113), TT (11.5 ± 4.33 nmol / l vs. 13.29 ± 4.15 nmol / l; p = 0.336),
BAT (6.04 ± 1.91 nmol / l vs. 7.37 ± 2.58 nmol / l; p = 0.173), and fT
(0.255 ± 0.078 nmol / l vs. 0.301 ± 0.104 nmol / l; p = 0.250).
In the 54 men, body mass index changes were inversely related
to SHBG levels (r = – 0.485; p < 0.001), but not to other indices of
testosterone status.
Discussion
▼
In overweight men with defi cient vitamin D status a signifi cant
increase in testosterone was observed after intake of 83 μ g vita-
min D daily for 1 year whereas there was no signifi cant change
in men receiving placebo. This work is, to the best of our knowl-
edge, the fi rst study, which specifi cally addresses the eff ect of
vitamin D supplementation on androgens in men. The results of
this study suggest that vitamin D supplementation might
increase testosterone levels in men. Our data support several
experimental and clinical fi ndings: First, VDR knockout mice
suff er from hypergonadotropic hypogonadism [2] . Second, vita-
min D status is directly associated with testosterone levels in
men [6] . Third, the male reproductive tract is a target tissue for
vitamin D eff ects [3] . The nonsignifi cant trend for seasonal dif-
ferences in both 25(OH)D and testosterone in the placebo group
supports our hypothesis of a vitamin D eff ect on testosterone.
In our study participants, mean baseline 25(OH)D values were in
the defi ciency range and mean testosterone values were at the
lower end of the reference range. Traditionally, low solar ultra-
violet B irradiation of the skin is a major cause of vitamin D defi -
ciency [1] . Both, vitamin D [1] and testosterone [5, 9] show
benefi cial eff ects on the musculoskeletal system. From an evolu-
tionary point of view it would make sense that an active lifestyle
(leading to an adequate skin synthesis of vitamin D) also has
benefi cial eff ects on muscle function, bone health, and the male
reproductive system. We are aware that no fi nal conclusions can
be drawn from our study regarding the eff ect of vitamin D sup-
plementation on testosterone in men but we do believe that our
work is of great importance because it provides a reasonable
rationale for future studies. Besides the marked increase in
25(OH)D levels in the vitamin D group, there was also a slight
(nonsignifi cant) increase in 25(OH)D in the placebo group dur-
ing follow-up. We assume that the similar decrease in PTH and
the similar trend for an increase in 1,25(OH)
2 D in both study
groups is due to a nonlinear association of these 2 calciotropic
hormones with increasing circulating 25(OH)D levels [10] , with
a pronounced eff ect at low and virtually no eff ect at high
25(OH)D levels. Nevertheless, the similar changes in these hor-
mones do not exclude group-specifi c eff ects on the reproductive
system, since nonclassical target tissues for vitamin D largely
depend on circulating 25(OH)D levels [1] , which diff ered mark-
edly between the vitamin D and placebo group.
Our study has both strengths and limitations. Strengths are the
study design, the use of a daily vitamin D dose that was eff ective
to increase 25(OH)D values from the defi ciency range into the
adequate range, and the fact that sample batching was per-
formed to avoid inter-assay variability. One limitation is the fact
that the eff ect of vitamin D supplementation on testosterone
was not a prespecifi ed study outcome and that we did not assess
testosterone-related functions such as libido, mood, or muscle
strengths. Another limitation is the relatively small number of
male study participants. In addition, future studies have to clar-
ify whether the vitamin D actions are mediated by a pituitary
eff ect or a testicular one.
In conclusion, our study results suggest that vitamin D supple-
mentation might increase testosterone levels in men. Further
randomized controlled trials are needed to confi rm this hypoth-
esis and to evaluate whether vitamin D driven increases in testos-
terone levels contribute to the vitamin D eff ects on various
health outcomes.
Acknowledgements
▼
We would like to thank Mrs. Marlen Ewald for excellent techni-
cal assistance.
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