Key Takeaway:


Vitamin D is helpful for supporting the immune system and may reduce susceptibility of Covid-19. Get a blood test to check vitamin D levels and supplement accordingly. Avoid taking over 4,000 IU per day and stay well.

Vitamin D in the summer

Normally I tell my clients they can stop taking a vitamin D supplement in the summer months if they are outside often. Vitamin D is actually a hormone that’s made when UV rays from the sun hit your skin. It travels throughout your body and gets transformed into the active form to work its magic. During winter months (October-April) the angle of the sun isn’t steep enough for the UV rays to stimulate vitamin D production. So like I said, if you’re outside for 10+ minutes a day (no sunscreen) with skin exposed you should get enough sun exposure to produce sufficient vitamin D.

If you are mostly indoors or wear sunscreen all the time, taking a vitamin D supplement even during the summer isn’t a bad idea. I get sunburnt from a flashlight thanks to my Swedish heritage so I wear sunscreen year-round, hence my summer vitamin D supplementation.

Get tested

Before you blindly start taking a supplement, get your vitamin D levels checked. You can take the appropriate dosage based on your blood levels to make sure you’re getting the right amount. Vitamin D is on our standard Gold panel which specific to athletes for optimal performance rather than a “normal” range based on a sedentary population.

You can also get a genetic test or combined blood and genetic test, that will tell you your genetic predisposition to vitamin D status. Once you have this information it can inform your food and supplement choices to make sure you’re in your sweet spot.

The link between vitamin D & Covid-19

Several studies like this one and this one have come out showing some interesting albeit not surprising correlations between vitamin D status and Covid-19 susceptibility and mortality. Vitamin D has been shown to protect against respiratory illness by supporting the immune system and anti-inflammatory pathways. As such, countries with more sun exposure (below 35 degrees latitude) had a lower mortality rate of Covid-19. The countries with the highest vitamin D deficiency had the highest levels of mortality, including Spain, France, and Italy. Obviously there are a lot of variables, but vitamin D may partly explain the higher mortality rates in some countries.

Based on the studies, supplement with no more than 4,000 IU per day, but again, this should be adjusted based on blood levels to achieve an optimal vitamin D status. The amount of supplement necessary to get there depends on current blood levels.

About Dr. A’nna

Dr. A’nna strives to inspire people to optimally fuel their body to achieve their best and have a positive impact on the world. She is the only combined Ph.D./RD specializing in sports performance nutrition in the world with all Ivy League degrees and the Chief Research Officer at AthleteBloodTest.

Dr. A’nna aims to cultivate a world of healthy athletes who understand nutrition and know how to leverage their physiology to get the best results in sports and life. You can reach her at [email protected] or on Instagram @drannaroby.

Categories: Supplements