The Almighty Vitamin D

It’s cold. It’s dark. It’s the middle of winter here in the northern hemisphere.

This means a few things: shorter days, more indoor workouts, and the need for more layers of clothing when venturing outside. All of these things coalesce into a common problem for health and performance: Vitamin D deficiency. There are a number of athlete-specific reasons we should be concerned about it, and if you’re just getting a single annual checkup in the summer, you may be missing it.

What is Vitamin D?

Vitamin D is a fat soluble vitamin and a hormone with widespread use throughout the body. There are two ways people can get Vitamin D, through exposure to sunlight and through diet. When sun exposure is sufficient, the body is able to produce all the vitamin D it needs. In winter, the warmth of the indoor trainer often beats the frozen, drippy-nosed outdoor rides. Not to mention the sun, depending on where you live, doesn’t stay out until dinnertime. We must find other sources of vitamin D to meet our needs, and food sources are limited. Good sources of Vitamin D include fatty fish, or fish liver oils, as well as fortified foods like milk, breakfast cereals, and orange juice, but often people don’t include these in their regular diets.

How Prevalent is Vitamin D Deficiency?

As someone who grew up in the Pacific Northwest, it’s safe to say Vitamin D deficiency can run rampant in the right conditions. Grey skies, 4:30pm sunsets, it can seem inevitable. By some estimates, around 40% of the US population may have Vitamin D deficiency. In the UK, one study has found deficiency rates over 70% in the general adult population. Highest rates of deficiency are usually seen in March which make sense given it’s the end of winter. The risk of deficiency increases at above the 400 north latitude, the upper half of the United States, people above 65 years of age, those that work or exercise indoors, and individuals with darker skin.

Symptoms of Deficiency

Many people with vitamin D deficiency may never notice symptoms, but that doesn’t mean deficiency isn’t impacting their health. The longer or more severe the deficiency, the more serious the effects can be. Key noticeable signs of deficiency are generalized muscle pain, fatigue, frequent illness, or stress fractures.

How Does Vitamin D Impact Health and Performance?

As previously mentioned, Vitamin D has a wide functionality across the body. It helps reduce inflammation, maintains calcium levels, and is crucial for bone health. Deficiency leads to lower bone density and increases the risk of stress fracture. Vitamin D is also thought to play an important role in immune function, as those deficient are more vulnerable to upper respiratory infections like the common cold and flu. This becomes especially important for endurance athletes who are already prone to more upper respiratory infections compared to nonathletes.

Individuals with suboptimal levels of Vitamin D were also more likely to experience a number of negative health and performance outcomes compared to non-deficient individuals. Low levels of Vitamin D have been linked to impaired lung function, asthma, and other chronic lung diseases. They were also more likely to experience decreased strength, muscle function, and delayed recovery. There have been a number of studies where deficient individuals supplemented with Vitamin D and then saw increases in both anaerobic and aerobic exercise capacity, as well as increases in cardiac muscle function. Winter is a time that many athletes take a break from racing and begin building a foundation for the next year. Ensuring adequate Vitamin D may provide an easy performance boost during this time and help support a solid base going into spring.

How to Assess Vitamin D Levels

Before taking any new supplement, it’s important to know your current levels. Vitamin D status is measured by testing serum 25(OH)D levels in the blood. You can ask your primary care doctor to order it, or there are also many at-home lab testing companies which can do it for you such as InsideTracker, Biostarks, and Athlete Blood Test. It’s not recommended to take a supplement without knowing your current levels, as this could lead to excess vitamin D accumulation, also known as vitamin D toxicity.

How to Treat a Vitamin D Deficiency

Since food sources of Vitamin D and sunlight aren’t known to cause toxicity, increasing these first is a good place to start. Try to get 5-30 minutes of sun exposure per day, and include more fatty fish, fortified milk, cereals, and orange juice into your diet. If your lab work comes back with suboptimal levels, your healthcare provider will be able to suggest ideal supplement doses to get you back to normal levels.

In the meantime, stay warm, eat enough, and hope that sunny, warm days aren’t too far off.

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