Am I Getting Enough Vitamin D?

In our most recent series, we explored why you might be low in iron, how to tell, and what to do about it. Now let’s look at another vital micronutrient: vitamin D. Like iron, it’s essential for performance and health, and yet many people are chronically deficient. Keep reading to learn which functions vitamin D performs, what happens when your levels dip, and how to get them back up again.

What does Vitamin D do for me?

Vitamin D helps us absorb calcium and phosphate from our intestines and then helps to regulate their storage & blood concentrations throughout our body, making it essential for the formation of new bone and the preservation of existing skeletal mass. Without enough Vitamin D, our bones can become brittle. Vitamin D is also involved in both innate and adaptive immunity, according to a team of British and Canadian researchers. It’s also involved in cardiovascular health and has a neuroprotective effect on the brain.

Why are so many of us Vitamin D deficient & how common is it?

It’s arguable that vitamin D is the most prevalent micronutrient deficiency. While many other vitamins and minerals can be consumed through a well-rounded diet, vitamin D’s production is mainly prompted by exposure to direct sunlight, and specifically UVB rays. We’ll look at some food sources in a moment, but Vitamin D is not prevalent in the foods we eat most often.  Combine that with the fact that American adults spend the majority of their time indoors, and it’s little wonder that up to 90 percent of the population is vitamin D deficient, per a paper published in Frontiers in Physiology.

I mostly train outside. Won't I get enough Vitamin D?

One would assume yes, but the research on vitamin D shows that even people who are active in sunny, warm climates have a high rate of deficiency. This is particularly prevalent in the Northern Hemisphere during winter, as the weak sun, cloudy weather, and early sunset conspire to keep us from synthesizing enough vitamin D. Plus, if you’re training in cold wintry conditions, you’re most likely layering up and covering parts of your body – like your hands and head – that are open to the sun at other times of year. Or, if you’re always running before the sun comes up, no Vitamin D production there. So just running outdoors might not be cutting it from a vitamin D standpoint.

How do I know if my Vitamin D is too low? What should my level be?

Vitamin D deficiency often has no symptoms at all. Symptoms may include fatigue, bone pain, muscle weakness, or mood changes. As some of these can be linked to other issues and multi-factorial, I often encourage my athletes to get a blood panel that includes serum vitamin D. I typically recommend that my athletes target 40 ng/mL or more. Anecdotally, around 75 percent of my athletes tested who are not supplementing have low Vitamin D. 

How can low Vitamin D impact my health & performance?

Insufficient vitamin D puts you at greater risk of getting sick and could prolong certain symptoms, which is not helpful from a performance standpoint. If you have a bone injury, it may take longer to heal if you have insufficient levels of Vitamin D. But perhaps the most concerning side effect of low vitamin D is the elevated incidence of stress fractures. 

A study of 802 NCAA Division 1 male and female athletes discovered that they increased their risk of stress fracture by 12% when their serum vitamin D was lower than 20 ng/mL and/or they didn’t take a vitamin D supplement, when compared to those whose serum vitamin D levels were >40 ng/mL and athletes with low vitamin D who were supplementing. The authors wrote that “Low vitamin D levels along with high-intensity athletic training may put an athlete at increased risk for a stress fracture.”

What can I do to increase my Vitamin D level?

If you know or suspect that you’re lacking in vitamin D, researchers from the University of Wyoming suggest a three-part strategy. First, try to get outside in direct sunlight for 5-30 minutes between 10 am and 3 pm as often as possible, as this is the easiest way to stimulate your body’s production. Skip the sunscreen for this short duration and try to get your sun session at least twice a week. (Note: We are not suggesting to skip your sunscreen altogether – as little as 5 minutes per day can help improve Vitamin D levels. If you are at high risk for skin cancer or have other skin conditions, this may not be an option for you, please consult your physician.) You can also try to eat more salmon, mackerel, tuna, and other oily fish, along with plenty of eggs (don’t toss the yolks!). As a bonus, these all provide inflammation-fighting omega-3 fatty acids. Animal foods like these contain D3, the most readily absorbed form, as do some fortified products like milk and cereal. Plant-based sources include leafy green vegetables, sesame seeds, and mushrooms, but these are in the D2 form, which has less bioavailability. 

Even the richest food sources are unlikely to supply the consistent amount of vitamin D you need, which is where a third tactic becomes useful: supplementation. 1,000 to 2,000 IUs of vitamin D3 per day is a solid starting point. Your doctor or dietitian might recommend more, depending on your situation. The NCAA researchers noted that if you’re low in vitamin D, supplementation helps elevate serum levels and reduces the risk of stress fracture. 

1. Emma L Bishop et al, “Vitamin D and Immune Regulation: Antibacterial, Antiviral, Anti-Inflammatory,” JBMR Plus, September 2020, available online at 2.Igor Bendik et al, “Vitamin D: A Critical and Essential Micronutrient for Human Health,” Frontiers in Physiology, July 2014, available online at 3.David Millward et al, “Association of Serum Vitamin D Levels and Stress Fractures in Collegiate Athletes,” Orthopaedic Journal of Sports Medicine, December 2020, available online at 4.Kentz S Willis et al, “Should We Be Concerned About the Vitamin D Status of Athletes?” International Journal of Sport Nutrition and Exercise Metabolism, April 2008, available online at

Disclaimer: The content in our blog articles provides generalized nutrition guidance. The information above may not apply to everyone. For personalized recommendations, please reach out to your sports dietitian. Individuals who may chose to implement nutrition changes agree that Featherstone Nutrition is not responsible for any injury, damage or loss related to those changes or participation.