Sunlight is the Key to Testosterone and Athletic Performance in Males

An athlete lifting weights in the gym
Unbeknown to most people, sunlight is a potent testosterone booster.

Today I want to share the results of a study conducted several decades ago that has forever changed the way we view the relationship between sunlight, testosterone, and athletic performance. In the study, Doctors Abraham Myerson and Rudolph Neustadt exposed men to UV light and measured the excretion of various sex hormones. The study revealed that exposure to UV light triggered huge increases in testosterone levels which did not return to baseline levels for over a week. This increase was dependent on the location of the body and the amount of skin exposed to the UV light. The researchers found that men’s baseline testosterone increased by 120% (more than double!) when the participants’ chest and back were exposed to UV light. However, the biggest increase in testosterone came when the participants’ testicles were exposed to UV light. The latter resulted in a massive 200% increase (triple) in baseline testosterone levels. This study has enormous implications for guys attempting to optimize testosterone levels and for athletes who want to maximize performance naturally and legally. It is a wonder why the sporting and fitness industries haven’t gone mainstream with this knowledge. Then again, there is little money to be made by advising people to get more sunlight. Companies would rather sell you expensive supplements. Athletes who have this knowledge may also wish to maintain a competitive advantage over their rivals.

The main takeaway of the study is that exposure to UV light anywhere on the body drives a huge increase in testosterone levels. I, however, wanted to test out the particulars of the study. Bluntly put, I wanted to see what would happen when I directly exposed the balls to UV light. I did this through an open window during the heat of day when the UV Index was high. I noticed they immediately began to grow upon first exposure. I knew this is the area where the body produces the vast majority of testosterone, so it made sense that local exposure to sunlight would trigger a disproportionate increase. The physical changes I observed coupled with the increases in energy and motivation to work out convinced me not only that the study was accurate, but that it was a major game-changer for the sports and fitness industries.

Exposing one’s nether parts to sunlight is neither practical nor desirable for obvious reasons. This has led some guys aware of the benefits to use UV red light therapy to achieve the same outcome in the privacy of their own home (link). I don’t doubt this works, but since it’s not something I’ve personally experimented with, I won’t say much about it. What I do know is that red light technology can be quiet pricey. However, I did discover a cheap and natural method that arguably worked even better for me than expensive alternatives.

Disclaimer: Don’t try this at home. You should consult your doctor about Vitamin D and testosterone optimization given that they are very powerful hormones and a lot could go wrong.

Vitamin D is known as the sunshine vitamin for good reason. The human body has a Vitamin D receptor in nearly ever cell of the body and is highly evolved to generate Vitamin D upon exposure to the sun. After I first read the study a few years ago, I wondered whether the increase in testosterone was triggered by the local production of Vitamin D directly on the skin in response to the UV light exposure. That in mind, I experimented with different doses of Vitamin D topical applied directly to the balls. Lo and behold, I noticed the same enlarging effect as when I had gotten direct UV light exposure. In this process of trial and error, I came to the conclusion that less is more. When the skin is exposed to UV light, it naturally generates Vitamin D in a uniform fashion. Small exposed areas of skin naturally produce small amounts of Vitamin D, and applying to much Vitamin D to any one region can interfere with its natural synthesis by the body. I found that less than 1,000 IU was enough for me to achieve the desired effect and that higher doses were wholly ineffective. Whenever I apply Vitamin D anywhere directly to my skin I prefer to crack open the Vitamin D softgels rather than purchase a topical product. My method is cheaper and it enables me to control the dosing better than prepared formulations. I would apply about half of a 1000 IU softgel every few days and could notice a major difference within a few hours.

Today I make sure I get adequate sun exposure as part of a healthy lifestyle, but I have not experimented with UV light or Vitamin D in this fashion in years. Currently, I have no reason to maintain peak testosterone levels. However, if I ever found myself training for an athletic competition or was experiencing symptoms of low testosterone, the power of the sun would be my first recourse. Nowadays people are quick to take supplements, inject steroids, or go on testosterone replacement therapy, giving up on their body’s natural ability to produce what they need. Meanwhile, nature offers a cheaper (if not free) solution that is arguably more effective than artificial alternatives. See my article on the The Most Natural Way To Optimize Vitamin D Levels for more pro tips on harnessing the power of the sun.


  1. Thanks a lot, this article was really helpfull. I tried it for my self and i must say that getting more sun light has a really big effect on my overall sex drive 🙂

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