Is Lack of Light and Vitamin D Killing Your Testosterone Levels?

Written by Andy Mobbs
featured image for article on vitamin d and testosterone

Testosterone is the male hormone responsible for a number of important roles, such as the development of the male reproductive system, muscle mass, facial hair, libido, and stronger bones. But there are certain factors that lead to low testosterone levels. In this article, we will look at whether vitamin D levels and sunlight exposure can affect testosterone levels.

The problem with low testosterone levels

Low testosterone is a problem for many people. And it’s actually getting worse with time. A 2007 study showed that men’s testosterone levels have been progressively getting lower with each passing decade since the 1980s (1).

chart showing general decline in testosterone

The question of course is why?

Certainly, our genetics have not changed in just a few years. So, we really need to look at lifestyle to see if there’s anything that could be responsible.

The lack of sunlight

With our busy lives and worries about skin cancer, many of us just don’t spend enough time in the sun. Doing so can be especially difficult for those living in regions that don’t get a lot of sun anyway!

A deficiency in Vitamin D

Vitamin D deficiency is a major public health issue. It has been associated with a whole range of health problems including musculoskeletal diseases, cardiovascular disease, cancer as well as infectious and autoimmune diseases (2).

In addition to this, there is a significant concentration of vitamin D receptors in the male reproductive tract. This includes the Leydig cells of the testes, which are the main source of testosterone production in men (3).

Is there an association between low Vitamin D and low testosterone levels?

Scientists are able to breed mice so that the gene that makes the Vitamin D receptor is removed. They are known as vitamin D receptor knockout mice. These mice can’t use vitamin D even if they have it, simply because they’re missing the receptor. This means they effectively have no vitamin D. And studies have shown that these mice have low fertility and low sperm counts (3).

In humans, 3 studies have shown an association between low vitamin D levels and low testosterone levels (4, 5, 6).

Also, a further study took 54 men with low testosterone and low vitamin D levels. Researchers gave half of them 3,322 IU of Vitamin D per day for a year. The other half of the men received a placebo.

At the end of the year, the placebo group exhibited no significant changes in their vitamin D or testosterone levels. However, for the men that supplemented with vitamin D, their vitamin D levels increased by 46%. Their testosterone levels also increased by 29%.

The study’s results suggest that increasing your vitamin D levels – either through diet, supplements, or sunshine exposure – can also increase your testosterone levels (7).

Is there an association between sunlight and low testosterone?

The study (7) also found that during the winter months, both vitamin D levels and testosterone levels drop. The question is, is it just a reduction in vitamin D that’s causing the drop in testosterone? Or are there other factors involved such as the reduction of light itself?

Let’s take a look at some studies:

Study 1

A 2013 study in male rats found that when they were exposed to continuous light for 70 days, they actually had higher levels of testosterone. They also had more 17β-HSD enzyme activity (this is the enzyme that produces testosterone and the DHEA precursor Androstenediol). Also, the rat’s testis grew in size and produced more sperm (8). These results suggest that not only vitamin D, but actually light itself is affecting testosterone levels.

Study 2

This study on humans looked at the levels of Luteinising hormone (LH) after exposure to bright light first thing in the morning. Whilst the study didn’t measure testosterone levels directly, LH is produced in the pituitary gland in the brain and travels to the testes to act on the Leydig cells causing them to produce testosterone (9).

The level of brightness of light can be measured in Lux. First, the researchers exposed the subjects to 1000 lux of light for 5 days. Then a further 5 days of a placebo light exposure of just 10 lux. These brightness levels were chosen after a previous study had found 1000 lux to improve the mood of depressed patients (10).

The subjects were exposed to light for 1 hour between 5 am – 6 am. Afterwards, they had the option to go back to sleep if they wanted to.

The researchers found that the 1000 lux light for 5 days led to a 69% increase in LH levels. On the other hand, the 5 days of placebo led to a reduction of LH levels back down to the initial starting point levels (11).

Study 3

Another study conducted all the way back in 1939 in Boston and published in the journal Endocrinology, found something similar (12). In the study, they used UV light and shone it mainly on the subject’s chest and stomach for 5 consecutive days. At the end of the 5 day period, they found that testosterone levels had increased by 128%.

After a rest period of 5 days, they found that testosterone levels had returned almost to the baseline that the subjects had started with at the beginning of the experiment. However, then they moved the light exposure to the testicles of the subjects and repeated the 5 days exposure. At the end of the exposure, they found that this time testosterone levels had increased 200% and that it then took 10 days for these levels to return to baseline levels!

How much Vitamin D and sunlight do you need?

The studies certainly indicate that both low vitamin D levels and low light exposure could keep testosterone levels low. So really how much vitamin D and light do you need?

Recommended sunlight exposure per day

The Endocrine Society recommends 15 – 30 minutes of direct sunlight per day. We would also recommend that there is direct light exposure as soon after waking up as possible. Also, it should be direct sunlight, as sunlight through windows can significantly reduce the intensity of the light.

Of course, direct sunlight can be difficult to get depending on where in the world you live especially during winter. For those that struggle, there are light lamps available that are relatively cheap.

We would recommend looking for a lamp with 10,000 lux and aiming at least initially for 30 minutes of exposure per day. Judging how you feel based on that, decide whether you should adjust the amount any further, either up or down.

Also for testosterone supercharge, you can try increasing light exposure to the testicles. You may do this through some naked sunbathing (best to be careful where you try this). Alternatively, try using a lamp.

Related article: 4 Reasons Why You Should Enjoy The Sun This Summer

Recommended vitamin D intake per day

For Vitamin D levels, the US Endocrine Society recommends between 30 – 50 ng/ml of vitamin D (13), measured in the storage form (25(OH)D), which is the standard form used on vitamin D tests. Do check you have the right units when looking at your tests. Ng/ml are the usual units in the US, whereas in Europe they normally use nmol/l.

It can be a little confusing, but to get nmol/l from ng/ml, you times the ng/ml figure by 2.5. So 30-50 ng/ml is 75-125 mol/l.

the vitamin d continuum
Image adapted from (14).

In terms of daily amounts of vitamin D needed, Michael Holick, one of the foremost experts on Vitamin D recommends 2000 IU per day for adults and 1000 IU per day for children (15).

Related article: What Causes Low Vitamin D Levels (Even When You’re Taking Vitamin D Supplements)?