August/September 2011 

Can vitamin D increase testosterone concentrations in men?

Researchers in Germany have conducted a randomized placebo-controlled study of vitamin D3 supplementation in overweight people who took part in a structured weight loss program for 12 months. They found that daily vitamin D3 at a dose of 3,333 IU did not affect weight loss. However, small but significant decreases in levels of triglycerides and the cytokine TNF-alpha occurred in the blood of people who received vitamin D3. Also, a small (+5%) but statistically significant increase in levels of bad cholesterol (LDL-C) occurred among vitamin D3 recipients. Unexpectedly, a small but statistically significant increase in testosterone levels was detected in men who received vitamin D3.

Study details

Two hundred HIV-negative overweight and otherwise healthy people were recruited for the weight loss study. As part of the program, participants were educated about nutrition and healthy eating habits and received weekly counselling via telephone with a nutritionist for the first six months of the study. Half of the participants received vitamin D3 at a dose of 3,333 IU/day for 12 consecutive months, while the other half received placebo. Among a subset of 54 men—31 received vitamin D and 23 received placebo—extensive laboratory assessments of testosterone were performed. This report focuses on the 54 men.

The average age of the men was 48 years and half of them smoked tobacco. Vitamin D levels prior to randomization were suggestive of deficiency, about 30 nmol/litre.


The men lost an average of 6 kg over the course of a year.

The men who received vitamin D had their levels rise to 86 nmol/litre.

Before we can present further results on testosterone, some background information is necessary.

About testosterone

In adult males, most testosterone (95%) is made by the testicles—between 3 mg and 10 mg each day. The adrenal glands produce the remaining amount of this hormone.

In the blood, most testosterone is bound to two proteins:

  • sex-hormone-binding globulin (SHBG)
  • albumin

In theory, only testosterone that has broken loose or becomes free from those previously mentioned proteins is available for use by tissues. This unbound testosterone is called “free testosterone” in laboratory tests.

Assessments of testosterone

Analysis of blood tests sometimes report testosterone assessments as follows:

  • total testosterone – this includes testosterone bound to blood proteins and free testosterone
  • free testosterone – this can be directly measured or calculated using total testosterone levels, SHBG and albumin concentration and equations
  • bioavailable testosterone – this refers to free testosterone plus testosterone loosely bound to albumin

Different laboratories have different reference ranges for testosterone, and levels of this hormone tend to fall with age.

Note that testosterone levels often fall in cases of chronic infections such as HIV and inflammatory conditions such as cancer, severe kidney and lung disease. Also, some drugs and substances can decrease testosterone levels, including the following:

  • chronic, excessive use of alcohol
  • chemotherapy
  • ketoconazole (Nizoral)
  • marijuana
  • spironolactone (Aldactone)

Results—Testosterone and vitamin D

In different assessments, participants who received vitamin D had relatively small but statistically significant increases in testosterone compared to placebo. For instance, total testosterone levels rose by 3 nmol/litre to 13.4 nmol/litre after 12 months. A similar trend occurred with bioavailable testosterone and free testosterone.

Why did an increase occur?

There are several pieces of evidence to suggest that vitamin D may have played a role in the increased testosterone levels detected in this study. Such evidence is important to consider because the primary purpose of the study was to assess weight loss and not to assess changes in testosterone. Moreover, the numbers of men in the substudy were relatively small. Here is some evidence that may support the vitamin D findings of this study:

  • In experiments on mice, those that do not have receptors for vitamin D suffer from less-than-normal levels of testosterone.
  • The testicles have receptors for vitamin D, suggesting that this vitamin plays some role there.
  • A previous cross-sectional study in people found a link between vitamin D levels in the blood and testosterone levels in the blood.

Taken together, these previous bits of research along with the present German study suggest that vitamin D may modestly alter testosterone levels in males. Because of the previously mentioned issues, the present study’s results cannot be taken as definitive, only suggestive. Also, because researchers did not assess factors influenced by testosterone, such as sex drive, mood or muscle strength, the clinical significance of these changes in testosterone levels is not clear.

Still, the findings from the present study are intriguing and require confirmation in a large randomized clinical trial.

—Sean R. Hosein


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