Should Cyclists Add a Vitamin D Supplement to Their Diet in Winter?

Yes, is the simple answer. Here's how, plus what all those studies linking Covid-19 and Vitamin D really mean.

BY SARAH SCHLICHTER, M.P.H., R.D.N. | 29 July 2021

In the summer, getting enough daily vitamin D, or the “sunshine vitamin,” can be easy when you’re consistently heading out for rides in the sun. But when the winter comes around, bringing with it early sunsets and gloomy winter rides, do you need to add supplements or foods with vitamin D to your diet?

And as we are all trying to stay healthy amidst the COVID-19 pandemic, you might’ve heard about research on COVID-19 survival rates and vitamin D intake. You might be wondering if you should up yours. Additionally, we’re spending more time than ever indoors, giving us fewer chances to get that necessary sunshine. (It’s important to keep in mind that there is currently no cure for COVID-19, and many treatment options are still in trial phases.)

What Is It?

First, a quick refresher: it is a fat-soluble vitamin and hormone that plays many roles in the body. You may be familiar with its regulation in bone structure, and while strong bones are certainly important for cyclists due to the high impact nature of the sport, it is also necessary for calcium absorption and fast-twitch muscle fibre function. It also modulates more than 2 000 genes involved in cellular growth, immune function, and protein synthesis.

These foods are common sources, according to the National Institutes of Health (NIH).

Fatty fish, like salmon (570 IU per 85g)
Rainbow trout (645 IU per 85g)
Fortified milk (120 IU per 1 cup)
Fortified cereal (80 IU per serving)
Eggs with yolks (44 IU per 1 large egg)
Raw, white mushrooms exposed to UV light (366 IU per 1/2 cup)
Dairy products like yogurt and cheese
Fortified orange juice

How Much Do You Need?

The recommended daily intake in the United States and Canada is 600 IU/day for children and adults up to 70 years of age. However, many experts question whether this amount is adequate, especially for the functions outside of bone health and athletic performance.

The Endocrine Society recommends 1 500-2 000 IU/day for individuals who are not getting adequate unprotected sun exposure, which amounts to five (for fair or light-skinned people) to 30 (for dark-skinned) people minutes of mid-day sunlight on the arms, legs, and back two to three times a week without sunscreen. (Though don’t use this as an excuse to not wear sunscreen!)

Getting that sun exposure in the winter months can difficult, especially in the northern half of the United States, because there is less sunlight, and people are wearing layers to stay warm. People do not necessarily need to increase IUs in the winter, but instead need to recognise that it will be difficult to obtain adequate Vitamin D from sunlight alone. Increasing the amount of vitamin D that comes from your diet, and potentially supplements, will be important.

Athletes who are not achieving regular sun exposure should have a plan in place for supplemental or a combination of dietary and supplemental Vitamin D. Consumption of fortified foods or an ordinary multivitamin alone is likely not enough for maintaining sufficient status. Many people will require supplements in the winter months (this is different from a regular multivitamin), though dietary sources and sunlight are still encouraged.

Cyclists looking to maintain optimal bone, muscle, and immune health for performance should pay attention to sources of vitamin D in their diets and can consider adding a supplement, especially in winter months. Athletes should always seek input from a doctor before adding supplements to their diet and be careful not to take a higher daily dose than recommended.

Who Is At Risk For Vitamin D Deficiency?

While the consumption of vitamin D rich foods is likely not enough, it can also be synthesised in the skin upon exposure to sunlight. However, in winter months, people typically spend less time outside and wear more clothing, making adequate exposure difficult.

Some populations also have a higher risk of vitamin D deficiency, including older individuals, those with a dark complexion (due to the pigment melanin), and athletes training and competing indoors. According to the Gatorade Sports Science Institute, Vitamin D supplementation is often necessary for athletes spending more time training indoors, and athletes who may not eat many dietary sources. Vitamin D status is generally lower in winter months due to the angle of the sun and insufficient sunlight (UVB) exposure.

Kelly Jones, M.S., R.D., C.S.S.D., recommends athletes see their doctors to get their vitamin D levels tested during summer or early fall to find out if they are deficient, even when they are able to get more sun exposure, in order to make a plan going into the winter months, noting that many people do not maintain healthy vitamin D levels even in the summer months. This can help athletes understand if they need to include more vitamin D in their diet, add a supplement, or increase sun exposure.

“Despite adequate sun exposure, many people may still not adequately create the active form of vitamin D,” Jones adds. “If athletes get tested before the winter months, they can have a plan in place for winter and pay special attention to vitamin D in their diets year-round.”

While there seems to be no universal consensus for Vitamin D deficiency, the NIH defines deficiency as blood levels below 30 nmol/L (12 ng/mL), but recommends levels above 50 nmol/L (20 ng/mL) for adequacy for both bone and overall health. It is important to note that these recommendations are for the general population.

The Gatorade Science Sports Institute defines deficiency as serum levels below 50 nmol/L (20 ng/mL), and recommends levels above 75 nmol/L (30-32 ng/mL) for adequacy. These numbers are geared specifically towards athletes.

Low levels of vitamin D can be linked with an increased risk of acute illness, inflammatory injuries, stress fractures, muscle pain and weakness and suboptimal muscle performance. Meaning, athletes need sufficient vitamin D levels for bone health and prevention of bone injuries and stress fractures.

“In addition to bone and skeletal health, vitamin D helps to regulate inflammation in the immune system and impacts hormones, thereby having the potential to influence mood,” Jones says. The former is important for keeping athletes healthy when they are doing tough workouts, and the latter can impact motivation and excitement for the sport.

A recent study published in Nutrients found that deficiency in athletes can have a negative impact on health and training efficiency. What’s more, a previous meta-analysis of 23 studies and more than 2 000 athletes showed nearly 56 percent of athletes had insufficient levels of vitamin D. Further research suggests that only 5 percent of college athletes meet the U.S. recommended daily intake from food alone, and Vitamin D deficiency (defined as <20 nm/mL or <50 nmol/L) in college athletes has been associated with upper respiratory illness during the winter and spring.

Will low levels affect your rides? In short, yes.

“Vitamin D is essential for training, performance and overall health, but many athletes don’t realise this,” adds Marita Radloff, R.D.N., and co-host of the Nail Your Nutrition podcast. “Inadequacies can affect lung function, VO2 max, and can even impact how well fast-twitch muscle fibres are maintained.”

Can Vitamin D Help Ward Off Coronavirus?

Since it plays a vital role in our immune and respiratory systems, it has also been studied for its connection with COVID-19. A handful of studies have shown a correlation between insufficiency and more severe symptoms of COVID-19, suggesting that it may be a prudent recommendation for reducing COVID-19 severity.

A recent study with over 190 000 participants published in PLoS One concluded that COVID-19 is strongly associated with circulating vitamin D levels. Another study of 200 patients hospitalised with COVID-19 found that more than 80 percent were diagnosed with vitamin D deficiency.

While the research does not prove a direct cause and effect relationship between vitamin D status and prevention, it does emphasise that it may be protective against COVID-19 complications, as well as the importance of sufficiency and the role it can play in immune health and overall health. However, more studies on larger populations need to be done before any conclusions can be drawn.