Vitamin D: You are my sunshine, my only sunshine!

In this second installment of the 4-part series on essential micronutrients for the endurance athlete, we will examine another important micronutrient used by the athlete’s body, what processes they impact, foods that increase our intake and standalone supplements. These micronutrients can be easily overlooked and that is why we have decided to focus some attention on these important nutrients.

Vitamin D

Over the past decade there has been an increased awareness of the impact of a relative Vitamin D deficiency in the medical community. I say relative because it is probably true that most adults consume enough Vitamin D in their diet but fail to convert the vitamin to its usable form in the body. During exposure to sunlight 7-dehydrocholesterol in the skin absorbs UVB radiation and is converted to pre-vitamin D3 which in turn isomerizes into vitamin D3. Pre-vitamin D3 and Vitamin D3 also absorb UVB radiation and are converted into a variety of photoproducts some of which have unique biologic properties. Sun induced Vitamin D synthesis is greatly influenced by season, time of day, latitude, altitude, air pollution, skin pigmentation, sunscreen use, passing through glass and plastic, and aging. Let’s just face this head on, most adults are spending less time outside than they did 50-years ago. When we do go outside for extended periods of time, we have been rightly conditioned to apply liberal amounts of sunscreen to protect ourselves from the damaging effects of the sun. That sunscreen application, as mentioned above, can significantly block the UVB rays that convert Vitamin D and therefore a deficiency can ensue.

It would seem that endurance athletes would be one of the least likely to become Vitamin D deficient since we typically most of our training outside, at least during the summer months, right? That is partially true depending on where you live and could drive a situation of early morning workouts (before the sun comes up … welcome to South Carolina) and even indoor training because of the heat. Then we have the winter up north driving us inside. Couple that with sunscreen use and other variables and one could quickly see how little sunlight we may be absorbing.

Now you know the mechanism of Vitamin D photosynthesis, but what does it really mean to me? Strong bones are important, but Vitamin D goes well beyond your bone strength and formation. There is much more scientific evidence that Vitamin D plays an additional role in sleep, increased immune function and muscle contraction. A study published in Dermatoendicrinology by British and Australian researchers, concluded that endurance athlete that supplementation in vitamin D deficient athletes improved their muscle regeneration and increased their speed, strength and power. That is a significant assumption for us that spend hundreds of hours a year trying to improve those metrics through training.

What do we do? Get tested the next time you are getting an annual physical with your physician. It is a simple blood test that can be added to your normal lab panel, but you will probably have to ask for it. If you are found deficient, your physician may prescribe a high-dose, prescription only (50,000 units) of Vitamin D to take weekly for 8-12 weeks to get you normalized before starting a maintenance regimen. Vitamin D rich foods include milk, yogurt margarines, cereals, catfish, sardines, salmon, tuna, and egg yolks. Not exactly the typical endurance athlete’s main diet choices, except for the fish, so supplementation may be warranted. The general guidelines recommend between 2000-5000 units of Vitamin D3 per day and is regarded as a safe daily dosage. There are many manufacturers of Vitamin D3 (cholecalciferol) and are readily available at your local drugstore. Furthermore, 20-30 minutes of direct sunlight per day (prior to sunscreen) is also recommended to photosynthesize Vitamin D. Keep in mind, as with all supplements, more is typically not better and can be dangerous… so please adhere to the above dosage guidelines unless otherwise instructed by your physician based on your personal Vitamin D level.

As an athlete, it is important to also consider the micronutrients that are essential to peak performance. Next, we will review our 3rd micronutrient, Calcium, it’s function in the athlete, foods to eat and supplementation.

Resources:

Saljoughian M. Vitamin D, the sunshine vitamin. US Pharm. 2011;36(4): HS-28-HS-32. https://www.uspharmacist.com/article/vitamin-d-the-sunshine-vitamin. Accessed August 28, 2022.

Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol. 2013; Jan 1:5(1):51-108. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/. Accessed August 29, 2022