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How low vitamin D hurts performance at the gym and in sport

Often, when you think of vitamin D you think of calcium and bone health. But it has many roles in the body besides promoting bone strength and growth: it’s involved in proper muscle functioning, strengthening the immune system, cardiovascular health, brain health, and much more.

Approximately 40% of the U.S. population does not get enough vitamin D. And only 44% of athletes reportedly meet their vitamin D needs.

These numbers could be even lower for those of us up here in Canada where temperatures are generally a little colder and we’re further away from the equator.

You might think, “so what?” Who cares if my vitamin D levels are a little low.

Vitamin D insufficiency can have some significant effects on your health and performance, especially if you’re an athlete or someone who works out regularly.

This article is going to dive into some of the science surrounding vitamin D in the athletic population to convince you that, unless you get sufficient vitamin D, you will never realize your full athletic potential.

But first…

How do you know if you’re low in vitamin D?

Having low levels of vitamin D can happen for a number of reasons. The most common ones have to do with your diet, how much sunlight you’re exposed to regularly, and the pigment of your skin.

Vegans are more likely to be deficient because most of the best dietary sources of vitamin D are from animals. These include fish and fish oils, egg yolks, fortified milk, and beef liver.

To make vitamin D, your body needs to be exposed to sunlight. People who are mostly homebound, live a good distance north of the equator, or generally spend most of their time with their skin well covered by clothes are at a greater risk of vitamin D deficiency.

Melanin is a pigment in the skin that makes it darker. Melanin reduces the skin’s ability to make vitamin D when exposed to the sun. Darker skin means more melanin, more melanin means less of an ability to make vitamin D. Less of an ability to make vitamin D means a greater risk of being vitamin D deficient. So, if you have darker skin, you’re more likely to have low vitamin D.

Recognizable symptoms of vitamin D deficiency are bone pain and muscle weakness. There are more subtle signs that are much more subtle and need to be diagnosed by a physician after they rule out other potential explanations.

How vitamin D deficiency affects your athletic performance

Vitamin D deficiency impacts athletic performance in two ways: 1) increased inflammation and immune system suppression leading to an increased risk of infection and delayed recovery from exercise and injury and 2) altered muscle strength and performance.

Increased inflammation and immune system suppression

The ability of vitamin D to influence the functioning of the immune system is no secret. It has been demonstrated many times before in animal and cellular studies.

Less is known about the affects of low vitamin D in the athletic and active populations.

According to one study, people who endurance train an average of 10 hours per week with low vitamin D levels experience more upper respiratory tract infections.

Upper respiratory tract infections involve:

  • Stuffy nose
  • Sore throat
  • Tonsillitis
  • Pharyngitis
  • Laryngitis
  • Sinusitis
  • Otitis media
  • The common cold

Other researchers have noticed a decrease in the immune system component Secretory Immunoglobulin A (SIgA) in athletes with low vitamin D.

SIgA is an antibody critical in protecting the mouth and nose, the lungs, and the guts from invading bugs.

Low vitamin D can also make active people and athletes more vulnerable to viral infection.

Cytokines are substances secreted by immune cells that act on other cells of the body and help them do things like defend themselves.

Two cytokines in particular, called IL-10 and IFN-γ, protect against viral infections. These two cytokines are lower in athletes with low vitamin D.

Together, these studies tell us that unless athletes and active people get enough vitamin D, they could be at a greater risk of getting sick, which could interrupt training and could impact recovery and adaptation to training stimuli.

Decreased muscle strength and performance

Pretty much all we know about the effect of vitamin D on muscle strength and performance comes from studies where athletes were given a vitamin D supplement. To my knowledge, no one has framed a study looking at muscle strength or performance in athletes with low vitamin D levels.

In 2015 a study was published showing that a single dose of vitamin D was associated with a 13% increase in quad and hamstring strength.

Ballet dancers given vitamin D experienced improvements in vertical jump and isometric quad strength.

While it hasn’t been directly tested experimentally, it is quite plausible that decreased vitamin D levels in athletes and active people would result in decreased muscle strength and performance.

How much is enough?

More work needs to be done to determine a dose of vitamin D adequate to meet the needs of athletes and highly active people. Until then, we have to rely on the recommendations set forth by the US Institute of Medicine, which is deemed accurate for 97.5% of individuals.

The current recommendation is an average daily intake of 10-20µg.

If you don’t get a lot of sun exposure, you live a good distance north of the equator, or you’re vegan, this number could be higher.

With these things taken into consideration, most experts agree that an average daily intake of 25-100µg should do the trick.


Vitamin D plays a significant role in general health. It is incredibly important for optimal performance in the gym and in sports because of its ability to reduce the risk of illness, prevent injury, and promote recovery and adaptation. Vitamin D supplementation has even been linked to increased muscle strength and performance in certain types of athletes.

Make sure you’re getting enough in your system by supplementing if you fall into one of the categories of people that could be at a particular risk for vitamin D deficiency. Or, if you’re experiencing any of the symptoms commonly noticed with vitamin D deficiency.


The Health Implications of Vitamin D Insufficiency and Low Energy Availability in Athletes

Vitamin D Deficiency

How Much Vitamin D Should You Take For Optimal Health?

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