Vitamin D: Consider A Supplement During Winter Months

November 10, 2020 | Illness, Sports Science

Dev Mishra, M.D.

President, Sideline Sports Doc

Medical Director, Apeiron Life

Fellow, American Academy of Orthopaedic Surgeons

Institute For Joint Restoration, Menlo Park, CA

November 10, 2020

Key Points:

  • Vitamin D is critically important for proper bone health, and likely plays a key role in many other systems required for proper health and sport performance
  • There is reasonable evidence that Vitamin D supplementation reduces the risk of contracting Covid-19
  • The main source of Vitamin D in our bodies comes from sunlight exposure
  • As the days grow shorter in the Northern hemisphere, most adults and children should consider a multivitamin supplement containing Vitamin D

Over the past weekend many parts of the U.S. turned their clocks backwards one hour, which means we are now in “Standard Time”.  I like to think of this as “daylight losing time”. Our afternoons get darker earlier. With fewer opportunities for sunlight exposure we’ve got fewer opportunities to make a critical component of health, fitness, and athletic performance: Vitamin D.

In addition to the general health benefits noted above there is reasonable evidence that a proper blood Vitamin D level can reduce the chance of testing positive for Covid-19.

In today’s post I’ll briefly describe where Vitamin D comes from, outline Vitamin D’s effects on sports performance and fitness, and what to do if you need to get more Vitamin D in your body.

Vitamin D comes from sun exposure, foods, and supplements

Many people are not aware that sun exposure is a key source of Vitamin D in our bodies. The amount of sun exposure needed is only about 15-20 minutes three times per week, but that can be challenging as sunlight in our day gets shorter.

There are some foods that contain Vitamin D but the amounts are generally not enough to fully provide the Vitamin D requirements for children and adults. Fatty fish such as swordfish and salmon are best. You might be surprised to know that milk and most other dairy products have very little Vitamin D in them naturally and they are “fortified” by adding Vitamin D to the final store bought version. In general, many nutritionists now believe that food sources are inadequate to meet our daily Vitamin D needs.

Which brings us to supplements. For most people who are either indoor athletes, or living this time of year north of the 37th Parallel (roughly from San Francisco to Virginia), you’ll likely need to get Vitamin D through nutritional supplements. A standard multivitamin is generally sufficient. The amount of Vitamin D needed varies by age, have a look at this chart for guidelines.

Effects of Low Vitamin D on Sports Performance

The effects of Vitamin D on bone health are well known. Adequate Vitamin D leads to proper bone health. Vitamin D also helps to improve calcium absorption and works with the parathyroid gland in complex bone health regulation.  These are strong cause and effect pathways.

It’s also believed that inadequate Vitamin D levels can influence the development of heart disease, hypertension, diabetes, and possibly some cancers. Many of these conditions are “associations” rather than cause and effect relationships.

The effects of low Vitamin D on sports performance are not as well known, but there is some research evidence to show that low vitamin D levels prolong muscle recovery from intense exercise, can lead to muscle atrophy, and negatively effect performance. Available evidence in these areas is weak but it’s at least plausible that these effects are real.

Possible Vitamin D Protective Effects For Covid-19 Virus

There is some controversy here, as a few studies have shown no benefit, but one study in the Journal of the American Medical Association showed a protective effect from Vitamin D supplementation in reducing Covid-19 risk. It seems that modest levels of supplementation have very little risk, and good potential upside.


Overall, there’s reason to believe that a very substantial portion of the U.S. population in all age groups is either deficient in Vitamin D or on the low end of normal. With that in mind, most people will benefit from a few steps:

  • Get the required sunlight if you can, 15-20 minutes 3 times per week
  • Use a standard daily multivitamin supplement which contains Vitamin D
  • If supplementing only Vitamin D, a good general rule is to supplement 600 IU up to age 70, and 800 IU if over age 70
  • Cold water fatty fish will also help your Vitamin D levels
  • If you’re an elite athlete consider a simple Vitamin D blood test to check your level




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