This is the first installment in a series.
Vitamin D is one of the most researched and talked about nutrients, and well it should be. Why? One reason is its long arm of influence: It has an impact on numerous essential bodily functions and conditions. Scientists keep discovering more information about how this unique vitamin, which is the only one the body produces by exposing the skin to sunlight, can affect our health.
Another reason why this nutrient is a hot topic is that vitamin D deficiency is common, which, given its critical role in overall health, is a big concern. I’m most interested in vitamin D for yet another reason: its involvement in increasing testosterone levels in men, as well as other general preventative health benefits.
Before I tackle the relationship between vitamin D and testosterone, I need to address several basics, which will clarify the bond between this vitamin and T.
What exactly is vitamin D?
Vitamin D is a fat-soluble vitamin, which means it is absorbed through the small intestine with dietary fat and is stored in body tissues. Because vitamin D is stored in the body longer (unlike water-soluble vitamins), taking excessively high doses as a supplement can cause toxicity.
How do we get vitamin D?
The best way to get vitamin D is from skin exposure to sunlight. That’s when a fascinating transformation process begins. When ultraviolet B rays hit your skin, a type of cholesterol naturally found in the skin, called 7-dehydrocholesterol, absorbs the ultraviolet B rays and is converted to cholecalciferol, the pre-vitamin form of vitamin D3. Cholecalciferol is transported to your liver, where it is metabolized and transformed into hydroxyvitamin D, aka 25-hydroxyvitamin D or 25(OH)D. The kidneys then convert the 25(OH)D into dihydroxyvitamin D, aka 25(OH)2D, the form of vitamin D your body can use.
The required amount of “skin exposure” is different for different people, but generally the body can produce 10,000 to 25,000 IU of vitamin D in the amount of time it takes for your skin to turn pink. You get the most bang for your buck when exposing a large area of unprotected skin (no sunscreen), such as your back, rather than just your face or arms. Factors such as time of day (best exposure time is between 10 a.m. and 3 p.m.), number of times per week of exposure (at least two to three times), skin type, and where you live also have an impact on the amount of vitamin D your body makes.
Vitamin D is also available from two other sources: diet and supplements. When you eat foods that contain vitamin D (e.g., fish such as salmon and herring, fortified beverages such as orange juice and nondairy drinks, fortified cereals) or take vitamin D supplements, your gut sends the vitamin to your liver, where it is transformed into an active form. However, it’s not feasible to get all the vitamin D you need from food, so unless you are spending enough time outdoors year-round, you will likely need to take a vitamin D3 supplement.
What are normal levels of vitamin D?
Before I talk about normal vitamin D levels and how much vitamin D you need to maintain a healthful amount, you should have a handle on how much vitamin D you already have. Some symptoms of vitamin D deficiency can include aches and pain and general tiredness, but some people don’t experience any symptoms at all. People with a severe deficiency of vitamin D may experience bone pain and weakness; but, again, not everyone has these symptoms.
If you think you may have a vitamin D deficiency, ask your doctor to check your vitamin D levels. This involves a simple blood test, which also can be ordered online through reputable laboratories. An optimum blood level of vitamin D, which will be displayed as 25(OH)D on your test results, is 50 ng/mL to 80 ng/mL, according to the Vitamin D Council and some other experts.
Personally, I advocate taking 5,000 IU+ daily (which is also endorsed by the Vitamin D Council). This figure is in dramatic contrast to the recommendation by the Food and Nutrition Board (the U.S. government), which is 600 IU for adults up to age 70 and 800 IU for older adults. If your vitamin D levels are very low, your doctor may prescribe a much higher dose for a short time (typically 50,000 IU) and then send you for another blood test to determine whether your dose should be adjusted.
Generally, people older than 50 need more vitamin D than do younger people. One reason is that as you age, your ability to convert ultraviolet rays to an active form of vitamin D declines, but your risk of BPH, type 2 diabetes, high blood pressure, prostate cancer and heart disease goes up. Aging men need to keep a sharp eye on their vitamin D levels and intake.
Can vitamin D increase testosterone concentrations in men?
The short answer is yes. Several studies suggest vitamin D can increase testosterone concentrations in men. A German research team, for example, gave 54 overweight, but otherwise healthy, men either a placebo (23 men) or 3,333 IU vitamin D per day (31 men) for 12 months. When the men entered the study, they were vitamin D-deficient (average of 30 nmol/L or 12 ng/mL). All the men also participated in a structured weight-loss program.
At the end of 12 months, the men who took vitamin D showed an increase in levels to an average of 86 nmol/L (34.5 ng/mL). These same men also had a small but significant increase in mean testosterone levels as well:
- Total testosterone, from 10.7 to 13.4 nmol/L
- Bioactive testosterone (free T plus T loosely bound to albumin), from 5.21 to 6.25 nmol/L
- Free testosterone, from 0.222 nmol/L to 0.267 nmol/L
The men who took placebo didn’t show any significant changes in testosterone or vitamin D. Based on these findings, the authors concluded that vitamin D supplements might increase levels of testosterone.
More recently, researchers presented study results at the American Urological Association 2015 Annual Meeting explaining that low levels of vitamin D are significantly and independently associated with low levels of testosterone in healthy middle-aged men. They arrived at this conclusion after analyzing blood sample data from 824 men.
Vitamin D levels [25(OH)D] levels were less than 30 ng/mL in 68 percent of the samples, yet only about 11 percent of men with these insufficient levels were taking supplements of vitamin D. This suggests that most men are not aware of the importance of keeping their vitamin D levels up.
When they looked at T levels, the experts found that total testosterone levels were higher among men who had normal levels of vitamin D than in men who had lower levels. Even after the investigators adjusted the data for cardiovascular risk factors, men with low vitamin D levels “still had significantly lower total testosterone than those with normal total testosterone.”
How does vitamin D increase T levels?
Exactly how vitamin D increases testosterone levels or why a vitamin D deficiency is associated with lower T is still a mystery. In fact, at the American Urological Association 2015 Annual Meeting, one of the presenters, Mary Ann McLaughlin, M.D., from the Mount Sinai Hospital in New York City, noted that earlier research in mice has shown that testosterone levels were lower in animals who had their vitamin D receptors genetically deleted. This, she said, “suggests that there is something about testosterone synthesis that needs vitamin D.” Exactly what that “something” is, is not yet known.
However, the researchers associated with the German study came up with several ideas about how vitamin D increases T levels based on their findings and those of other investigators.
- Experiments in mice have indicated that those who don’t have receptors for the vitamin have abnormally low levels of testosterone.
- Your testicles have receptors for vitamin D, which suggests the vitamin has an important role in the function of this gland.
- Results of a 2013 cross-sectional study found a positive link between blood levels of vitamin D and both total and free testosterone in 1,362 men who participated in the Health Professionals Follow-up Study. The authors emphasized that “possible causality and direction of the vitamin D-testosterone association deserve further scientific investigation.”