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Everything You Need To Know About Vitamin D Supplementation

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Vitamin D is an often overlooked nutrient in sports nutrition. This is a mistake because studies show that optimizing vitamin D levels can improve athletic performance and protect against injury and illness. This article will provide important information about vitamin D metabolism and give you pointers for making sure you are getting enough.

How Do We Get Vitamin D?

Vitamin D is supplied from two different sources: The body makes it in response to sun exposure or we get it from the diet.

Once the skin is exposed to the sun’s ultraviolet B radiation, it converts cholesterol into vitamin D. The recommended dosage of sunlight exposure during the summer to provide sufficient vitamin D is 5 to 20 minutes a day to exposed skin (without sunscreen). Fifteen minutes of sun exposure during the summer months in a bathing suit leads the body to produce 10,000 to 20,000 IUs of vitamin D.

Vitamin D is also available from food, with cod liver oil, wild salmon, and sun-dried shiitake mushrooms supplying significant amounts (about 1,000 IUs per serving). Unfortunately, for people who get little sun exposure, dietary vitamin D is rarely sufficient to maintain a healthy level and deficiency is extremely common.

Who Is At Risk Of Vitamin D Deficiency?


A recent analysis from 23 studies of 2313 athletes found that 56 percent had low vitamin D. Sports-specific studies found that 93 percent of basketball players and 83 percent of gymnasts were deficient in vitamin D. According to the most recent NHANES study, 77 percent of Americans have inadequate vitamin D.

Meanwhile, people with dark skin color are at greater risk of vitamin D deficiency than Caucasians due to the fact that the melanin in darker skin blocks vitamin D production. For example, a 2010 survey of Americans found that 70 percent of whites but 93 percent of blacks were deficient in vitamin D.

Besides skin color, other factors that reduce the body’s ability to produce vitamin D include living at latitudes that are further away from the equator (32-42 ° North or South), wearing sunscreen or sunglasses, cloudy climates, thick ozone layer due to pollution, being obese, or being elderly.

What Is The Optimal Dosage?

Experts disagree on reference ranges for optimal vitamin D status. The Endocrine Society classifies anything below 20 ng/ml to be deficient and a range of 20 to 30 ng/ml to be insufficient. A “deficiency” is more severe than an “insufficiency,” which is defined as the range of marginal deficiency and is not high enough to protect against chronic diseases.

Sports medicine scientists from Marshall University consider 50 ng/ml the minimal amount for athletic performance enhancement and a value of 40 ng/ml as ideal for preventing fractures.

These recommendations are based on the fact that once vitamin D levels reach 32 ng/ml, parathyroid hormones become stable and intestinal calcium absorption is enhanced, reducing the risk of bone loss. At higher levels above 40 ng/ml, vitamin D begins to be stored in the muscle and fat for future use. This allows for all immediate metabolic needs to be fulfilled without daily replenishment of vitamin D to satisfy requirements.

Are There Nutrients That Are Synergistic With Vitamin D?

Any discussion of vitamin D merits mention of calcium, vitamin K, and magnesium because all three work synergistically with vitamin D. Both vitamin K2 and calcium improve the bone-building effects of vitamin D. When vitamin K2 levels are inadequate, there is a buildup of inactive bone building proteins, which leads to the release of calcium from bone, increasing bone loss. This calcium is then deposited in soft tissues, causing arterial calcification.

This is important because vitamin K stores are rapidly depleted without a constant supply, and most people don’t get enough vitamin K2 to begin with.. Further, most people don't get enough vitamin K2, which is the more bioavailable form. It is present in a variety of fish, offal, meat, dairy products, and fermented cheese (blue cheese) and soy (natto).

The Institute of Medicine recommends a daily intake of 90 mcg of vitamin K for women and 120 mcg for men. Interestingly, a much larger dose of 10 mg of vitamin K (10,000 mcg) daily was found to be beneficial for elite female marathon runners to increase bone formation. A vitamin K2 variant, called MK4 has been shown to be especially effective for preventing osteoporosis in postmenopausal women. Therefore, athletes at risk of bone loss, such as runners, swimmers, gymnasts, and physique athletes may benefit from combing vitamin D with an MK4 supplement.

Magnesium is another nutrient that works synergistically with calcium and vitamin D. Magnesium leads to the release of the hormone calcitonin, which helps to preserve bone structure and draws calcium out of the blood and soft tissues and back into bone. A healthy calcium to magnesium intake is 1:1, which means that if you are getting around 500 mg of magnesium, as commonly recommended for athletes, a near equal intake of calcium is indicated.

What About Toxicity? How Do I Avoid Getting Too Much?

There has never been a reported case of vitamin D toxicity from overexposure to the sun. Serum levels of vitamin D in individuals living close to the equator and working outdoors are often around 50 ng/ml, supporting the theory that toxicity from the sun is extremely unlikely.

Nonetheless, there have been cases of toxicity due to over supplementation, often from someone accidently taking more than they intended. For example, when two elderly patients accidentally took 2,000,000 IUs (yes, 2 million) of vitamin D they had no adverse effects, but did experience slightly elevated blood calcium levels.

When you have too much vitamin D in your body, your liver produces too much of a chemical called 25(OH)D, which can cause high levels of calcium to develop in your blood. This could lead to kidney stones, hardening of the arteries, and bone loss over time.

To put your mind at ease and ensure you’re getting enough vitamin D for peak performance, follow these simple steps.

1: Get your vitamin D measured by your doctor.

When you get your next physical, ask your doctor to measure your vitamin D and tell you what it is.

2: If you are deficient in vitamin D (below 30 ng/ml) work with your doctor to establish a supplementation protocol. One group of scientists recommend supplementing with 50,000 IUs per week for 8 weeks. A more conservative approach is to take 5,000 IUS daily for 3 months.

3: Adjust vitamin D according to blood tests.

Get another vitamin D test after 2 to 3 months. Once a sufficient level is achieved, continued supplementation of up to 4,000 IUs a day is recommended for adolescents and adults by the National Academy of Sciences.

4: Test Vitamin K and magnesium.

It’s a wise practice to measure vitamin K and red blood cell levels of magnesium at the same time that you test your vitamin D. All these nutrients are fat-soluble, and scientists believe they work together in the body to promote optimal health and performance.


Dahlquist, D., et al. Plausible ergogenic effects of vitamin D on athletic performance and recovery. Journal of the International Society of Sports Nutrition. 2015. 12(33).

Ogan, D., Pritchett, K. Vitamin D and the Athlete. Nutrients. 2013. 5, 1856-1868.

Shuler, F., et al. Sports Health Benefits of Vitamin D. Sports Health. 2012. 4(6): 496–501.

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