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Can Vitamin D Affect Your Performance?

BY Carrie McCusker

Vitamin D deficiency has been linked to everything from bone and muscle health to emotional wellbeing. Here's how to monitor it and make sure you're getting enough.

Warm sun on bare skin not only feels good, but also allows the human body to produce Vitamin D, a secosteroid hormone that is created in the skin after exposure to UVB radiation. Vitamin D has been extensively researched and shown to be important for bone health, muscle growth, recovery and immune function—including battling viral infections. Vitamin D has been correlated with lower blood pressure and heart health, and even emotional wellbeing. Athletes interested in maximizing their performance should consider that while some of the data is inconclusive, a lot points towards Vitamin D as a player that could positively influence performance.

80-90% of Vitamin D needs are met by UVB exposure, and only 10-20% comes from dietary sources. Since most working adults spend most of the daylight hours indoors, it is no surprise that Vitamin D deficiency is extremely common. By some estimates, up to 80% of the world’s population is lacking. “…Vitamin D deficiency is becoming an epidemic across the USA, even among groups that were not previously labeled as “at-risk.”

Athletes should take note: even very recent studies suggest deficiency can affect muscle function and strength along with negative impacts on bone health and healing.

Are you at risk?

It may be surprising to learn that not all sunny times of the day are equal. The skin requires exposure to UVB rays, which are only present in the atmosphere when the sun reaches 35 degrees, otherwise known as solar noon. For individuals living above north latitude 35 degrees, the sun literally does not reach the necessary angle for UVB penetration for all of the winter months, meaning zero opportunity for D production. Even during peak times, wearing sunscreen or skin-covering clothing can prevent production.

Furthermore, an individual’s physical characteristics including darker skin tones, higher body fat, and age (over 50) can also lead to slower Vitamin D production times and more risk of deficiency. Athletes who train predominantly indoors or during off-peak hours are as at-risk as those who work indoors or don’t get outside during the day. Exercise itself does not promote Vitamin D production.

How much is normal?

The USA requirement is for 600 IU/day, but there are studies of the athlete population that suggest that is not enough for activation of the immune system. If looking at amounts in the blood, in line with the latest guidelines, the normal ranges for serum 25(OH)D levels are defined as 30–50 ng/mL or 40–60 ng/mL. Vitamin D insufficiency is defined as serum levels of 20–30 ng/mL and Vitamin D deficiency as serum levels below 20 ng/mL.

Unlike many other vitamins that you track by monitoring diet, Vitamin D can remain a mystery unless a blood test is administered. If you suspect you have a deficiency, you can talk to a doctor, or take matters into your own hands first and check out online testing like Everlywell. This $79 Vitamin D test kit works through a simple finger prick from the comfort of your own home—simply gather a few drops of blood to send back to their labs. 

What can you do?

One really cool app released in 2017 is called dminder. It will literally track your Vitamin D based on individual skin tone, age, weight and amount of skin exposed. You can enter supplements, and the app will use your geographical location and current time to help coordinate getting outside to maximize UVB rays but also prevent sunburn. The data is saved and calculated so at a glance you know if needs are being met. Remember, we only need around 15 minutes a day, several days a week, so it’s not a huge time commitment.

Don’t forget the 10-20% of Vitamin D in your diet. Check labels; most cereals, orange juice and plant milks are fortified with enough Vitamin D to meet your needs. Tofu is another nutrient-dense option. Mushrooms, especially those that have spent time in UV light from the sun or a lamp are high in Vitamin D. Finally, if you live where fresh, sustainable seafood is available, most of it qualifies as a good source of Vitamin D.

You can also consider a supplement, but you should always chat with your doctor before incorporating it into your diet. Tara Pelletier, a primary care physician in the northeast, told me it is very unusual to overdose on Vitamin D. Her only experience was someone taking fish oil and high doses of Vitamin D supplements at the same time. “If you live in the sun sparse northern hemisphere, taking a dose 2000-4000 iu/d is worth trying from November to March.” 

Because Vitamin D is predominantly created by UVB rays from the sun, a lot of the population is deficient due to sunscreen use, time indoors, or geographical location. Research on the vital role Vitamin D plays in our bodies is ongoing, but the risk of side effects from supplements is low. With potential benefits to the immune system and muscle repair due to the presence of this vitamin, it’s wise for athletes to explore their own intake or production through the use of sun, supplements, diet, and medical consultation.

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About Carrie McCusker

Carrie McCusker is a level 2 TrainingPeaks coach and a lifelong athlete who enjoys bringing individual attention to every level of athlete. You can find her on Strava and Instagram or check out her coach profile at TrainingPeaks.

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