Nutrition Q & A Vitamin D – The Sunshine Vitamin. Do I need to supplement?

Question: I’ve heard a lot lately about the prevalence of Vitamin D deficiencies and the need to take supplements. Should I be taking Vitamin D? As an athlete, is there any harm to being deficient or any positive benefits in having adequate levels?

Answer: The short answer is yes, yes and yes.

Without going into a lengthy, scientific description, Vitamin D is a unique nutrient that can be obtained entirely from the UVB rays of the sun via the skin. Your body converts an initial form to a usable form necessary to the function of various tissues in the body. Long-known targets include bone, intestine and parathyroid gland and recently discovered targets include prostate gland, breast and colon cells, immune cells, pancreas (beta) cells and muscle cells. As you can see, the impacts of Vitamin D are far-reaching for a healthy, strong body. On the other hand, insufficient Vitamin D levels may negatively impact bone health, immunity, muscle strength, inflammatory responses and, ultimately, athletic performance.

Does where I live matter?

There is an unfortunate reality that plagues at least half of the world’s population: Vitamin D absorption and synthesis is greatly reduced if you don’t get enough sun, and it’s hard to get that sun exposure at greater than 35° N or S latitude. That means if you live anywhere greater than that latitude your risk of developing a Vitamin D deficiency increases. Where do you live and train? Draw a horizontal line from central California across the top of Arizona, New Mexico and continue until you reach the east coast of North Carolina. If you live and train in North America North of the line you are a candidate for Vitamin D supplementation. If you live South of the line, 20-30 minutes of sun exposure to your extremities without sunscreen, 3-5 times per week will generally be enough time to provide for adequate Vitamin D levels.

Are you among the deficient?

Worldwide, the prevalence of Vitamin D deficiency among the young and old alike is very high; athletes are no exception. However, there is less data in the athletic population – but this is changing rapidly. In a preliminary study, 40% of adult distance runners who trained outdoors in Baton Rouge, LA (latitude 30°) were found to have insufficient levels of Vitamin D. So, even in locations residing less than the 35° parallel, people are susceptible to having low Vitamin D levels.

If you’ve been tested, compare your results

Reference values for 25(OH) Vitamin D:

  • Deficient <20ng/mL
  • Insufficiency <32ng/mL
  • Sufficient =>32ng/mL
  • Ideal = 40-70 ng/mL (may be higher)
  • Toxicity >150ng/mL

Causes & Consequences:

Causes of Vitamin D deficiency can be linked to a variety of reasons, such as a reduction in dietary intake, less sun exposure, increased sunscreen, variable calcium intake, and endocrine factors, among other unknown variables.

While you might not be considering the health consequences of being deficient in Vitamin D, you may be interested in the effect your Vitamin D status has on muscle strength and function (power & force), VO2 max, and hypertrophy of muscle fibers. There is limited but emerging evidence that a relationship between Vitamin D status, muscle function and athletic performance in young, healthy athletes does exist. In the last two to three years, several studies in peer-reviewed scientific journals have shown that Vitamin D supplementation may influence muscle function, contractile properties and fiber type, as well as increase peak power thereby increasing athletic performance. In 2009, Cannell J et al. found that reaction times improved significantly with 3 weeks of UV radiation exposure compared with the non-irradiated group. Reaction times slowly worsened as autumn progressed, revealing that sun exposure and ultimately Vitamin D status correlated with better performance (Med Sci Sports Exerc). Stay tuned for more Vitamin D and athletic performance research – it’s coming down the pipeline.

Bridging the gap:

A sports dietitian along with your primary care provider can help you determine your Vitamin D status and if you require supplementation. A complete nutrition assessment will include anthropometric measurements, biochemical tests, clinical findings, dietary evaluation and environmental considerations. Components to be taken into consideration include assessing body composition and bone density, 25-hydroxy Vitamin D (25 [OH] D) and parathyroid concentrations, muscle and bone pain, dietary intake, sun exposure, sunscreen use, training status, showering habits and geographic location.

Can’t I get enough from my food?

Dietary Sources of Vitamin D are limited to fatty fish, eggs, fortified products and mushrooms. It is now believed that the RDA for Vitamin D of 200 International Units (IU) is far too low. Revisions to the recommendations are currently being studied. A level of 1,000-2,000 IU per day is more likely the required amount to prevent deficiencies and maintain normal levels.

Sample list of Vitamin D containing foods:

Cod Liver Oil1 Tbsp1300 IU
Wild Salmon3.5 oz980 IU
Sun Dried Shiitake Mushrooms1 oz400-500 IU
Canned Sardines3.5 oz270 IU
Farmed Salmon3.5 oz250 IU
Tuna Steak3.5 oz165 IU
Milk, Fortified1 cup100 IU
Orange Juice, Fortified1 cup100 IU
Cod3.5 oz80 IU
Margarine, Fortified1 Tbsp8-80 IU
Cereal, Fortified¾ -1 Cup40 IU
Egg Yolk120 IU

The likelihood of reaching the newly suggested intake of 1,000-2,000 IU/day from food sources is a reach at best; therefore supplementation is nearly inevitable especially for those living at greater than 35° N or S latitude.

If a deficiency is found, a discussion with your primary care provider is recommended to devise a treatment protocol – depending on the degree of deficiency. Treatment options may include:

  • D3 (Cholecalciferol) available OTC in 1000, 2000, 5000, 10,000, and 50,000 IU
  • Multivitamin, generally provides 400 IU, up to 1000 IU
  • D2 (Ergocalciferol) available by prescription in 50,000 IU
  • Cod liver oil, but may be too high in vitamin A
  • D3 more effective than D2 at higher doses and less likely to be toxic


You can perform a quick checklist to assess your Vitamin D status. If you answer yes to two or more questions, it’s likely you need to take supplemental Vitamin D. If you answer yes to more than 5 questions you may be deficient, thus requiring higher doses of Vitamin D to reach adequate and/or optimal levels.

What if I don’t have a doctor or a sports dietitian to assess my Vitamin D status?

Do the checklist:

1. Do you live above 35° N or S latitude?          YES / NO

2. Do you exercise indoors?        YES / NO

3. Do you exercise outdoors but with no skin exposed?    YES / NO

4. Do you rarely eat fatty fish, eggs, milk or fortified Vitamin D foods?  YES / NO

5. Do you wear sunscreen of SPF 15 or greater?     YES / NO

6. Do you shower soon after getting sun exposure?     YES / NO

7. Do you have any malabsorption (gastrointestinal) problems?   YES / NO

8. Do you take any medications?       YES / NO

9. Do you have celiac disease or Crohn’s disease?     YES / NO

The bottom line:

Taking vitamin and mineral supplements is only necessary if adequate amounts can’t be obtained from the diet, if absorption is a problem, or if a deficiency is already present. It’s clear that it is difficult to meet daily Vitamin D recommendations from diet alone; unless you are eating wild salmon daily – a rather expensive eating habit! So, while Vitamin D has been coined the sunshine vitamin it might not be depending on where you call home.

Levels of 25 (OH) D of at least 32ng/mL but preferably 50ng/ml may be maintained by safe sun exposure (20-30 minutes 3-5x/week at greater than 35°) or a Vitamin D supplement of 1,000-5,000 IU/day. All athletes living at greater than 35° N or S latitude need Vitamin D supplementation during the winter months. If you’ve had a history of stress fractures, frequent illness, bone and joint injury, or muscle pain, nutrition assessment of Vitamin D status may be beneficial in preventing or correcting these issues.

Unless you are planning a sunny tropical vacation on a monthly basis I would suggest getting a bottle of sunshine – it’s definitely worth it.