It’s the middle of winter, and the days are dark and cold. But you’re still training intensely and eating clean to get ready for your upcoming competition. Unfortunately, there is one vitamin no amount of clean eating can fix, especially in athletes. New research suggests maintaining the right levels of vitamin D may improve several elements of performance, including your VO2 max, sprint capacity, and power production.


A Growing Research Field

Exercise dramatically increases an athlete’s demand for vitamin D, as your muscle, heart, and vascular tissue all contain key vitamin D receptors. Today, studies show more than 50 percent of athletes are low in vitamin D.1 While the direct cause isn’t clear, it’s most likely a combination of things like inflammatory processes, muscular damage, increased protein synthesis requirements, increased immune activity, lack of sun exposure, race, and genetics.2


A clear vitamin D deficiency occurs at blood levels less than 20ng/mL (< 50 nmol/L), while insufficiency for athletes is generally defined at blood levels between 20-32 ng/mL (50-80 nmol/L). Insufficiency simply means you’re not getting enough to meet the demands of your activity. Intense training is demanding. New research suggests that 40-50ng/mL (100-125 nmol/L) seems to be the “sweet spot” for supporting optimal athletic performance, and experts agree the body needs daily replenishment to meet that requirement.3,4


Achieving your ideal vitamin D intake may upgrade six key areas of performance:


  1. VO2 max
  2. Muscular power production
  3. Testosterone levels
  4. Inflammation
  5. Susceptibility to colds and flu
  6. Mood


Let’s take a closer look at each.


Maintaining the right level of vitamin D may improve your sprint capacity.

Can adding more vitamin D to your diet make you a sprinting powerhouse like Dan Bailey?


1. VO2 Max

You likely spend a lot of time planning and periodizing your training to maximize your efforts, but did you know that not having enough vitamin D could compromise your maximal oxygen uptake, or VO2 max, a classic marker for assessing aerobic fitness? New research in professional hockey and soccer players found a strong correlation between low vitamin D status and VO2 max. If you’re a weekend warrior, this relationship may be even stronger.


Experts will tell you just because there is an association doesn’t mean that increasing the amount of vitamin D in your diet will improve performance. However, a new study in vitamin D deficient rowers found that 8 weeks of supplementation (6,000IU per day) resulted in more than a 10 percent improvement of VO2 max. For elite athletes, improving performance by 2-3 percent is the difference between a podium finish and being in the middle of the pack.5,6,7 Remember, more is not always better. Talk to your doctor and get tested before supplementing with high doses of vitamin D.


2. Power Production

Your muscle tissues have many key receptor sites for vitamin D, and they seem to play a key role in supporting power production. For athletes, increasing power production translates to improved performance on the playing field. Recently, the Canadian Women’s National Hockey strength and conditioning team found athletes with higher power production were more likely to make the final selection for the national team.


Additionally, a study in soccer players found increasing baseline vitamin D status over an 8-week period resulted in an increase in 10-meter sprint times and vertical jump.8 While not all studies found this relationship, it’s important to ensure you meet the minimal baseline requirements to ensure maximum training benefit.


3. Testosterone Levels

Low testosterone is a common symptom in athletes who are over-reaching and overtraining. Unfortunately, too many people look for a quick fix rather than address why their testosterone levels are low in the first place. Vitamin D is a precursor to testosterone production and may increase the binding efficiency of testosterone to its receptors.4 Low levels are linked to increased protein breakdown, reduced strength, and increased body fat.


If you’re an athlete over age sixty, the connection is even more compelling because low vitamin D levels at that age correlate strongly to low testosterone levels.9 A new study over a 12-month time span found that adding approximately 3,000 IU of vitamin D daily resulted in increased total, bioavailable, and free testosterone.10 For those training through the winter, low testosterone combined with intense training will lead to sub-optimal recovery and increased risk of symptoms of overtraining (i.e., increased muscle soreness, low mood, fatigue, low libido, etc.). This is especially true for athletes who compete in indoor sports year round that limit sun exposure.


4. Inflammation

Inflammation is a natural product of intense training. However, too much inflammation can impair muscular function and future performance. One study showed adding an extra 4,000 IU of vitamin D daily can offset the increased inflammatory reaction with a high-volume training load of 10 sets of 10 reps of compound exercises in men and women.11


Interestingly, the group adding extra vitamin D also noted a mere 6 percent drop in power output over the course of the workout, while the group not supplementing had a 32 percent decrease in power. Amazingly, this deficit lasted for up to 48 hours. If you’re preparing for a competition or the CrossFit Games, maintaining power output during competition is critical to your performance.


5. Colds and Flu

There is nothing worse than catching a cold or flu in the days leading up to a competition. All those hard training days and dedication to be at the top of your game, only to be cut short by a nasty bug. If you’re low in vitamin D, the “foot soldier” immune cells that make up your innate immune system will also be low. If this first-line of immune defense is compromised, you’ll be at increased risk of infection.12


Vitamin D promotes hundreds of anti-microbial proteins in the body that fight off bacteria and viruses and helps keep your immune system robust in the build-up to competition. Research in athletic populations highlights that maintaining optimal levels of vitamin D can reduce common infectious illnesses.13 If your levels are low, your immunity and performance will likely be compromised.


6. Mood

Training intensely isn’t just tough on your muscles and joints. It also takes a toll on your mental game. If you're an athlete, you regularly push that fine line between over-reaching (pushing beyond your limits to grow stronger) and overtraining (pushing too far beyond your limits). Therefore, it’s crucial to maintain a positive mood as you fight through the toughest weeks of your training.


Low levels of vitamin D are consistently associated with low mood and depression, and because many athletes train indoors through the winter months (and sometimes even summer, depending on your sport), deficient levels can impair you sense of well-being.14 Cognitive decline also impacts your decision-making abilities, which are crucial in the heat of competition, yet fatigue and pain make them very difficult.


The sun is your best source of vitamin D.

The best source of vitamin D is free. Take advantage when the sun is shining and get outside.


Sources of Vitamin D

Now that you know vitamin D is key for optimal performance, where is the best place to get it? The sun is far and away your best source of vitamin D. Fifteen minutes of exposure on 5 percent of your skin leads to 10,000-20,000 IU of vitamin D production.4 If you live in a city with a true winter – north of the 42nd parallel – you’ll need more than sun exposure alone to meet your demands, as the sun isn’t high enough in the sky for an adequate dose.


Including vitamin D rich foods in your diet should always be your foundation, and the best dietary sources include egg yolks, pork (yes, bacon!), mushrooms, fortified milk, and yogurt (if you struggle to digest dairy effectively, discontinue).


Of course, if you live in a city with a true winter climate, food alone won’t meet your demands. The general recommendation for supplementing with vitamin D during winter is 1,000-2,000 IU per day. However, this is the case for the general population, not athletes. The research on athletes suggests between 4,000-6,000 IU of vitamin D3 daily is a good bet, however this should only be taken during your intense training phases (up to 8-12 weeks), or from November to March. If you decide to take vitamin D doses greater than 2,000 IU, you must get regular blood tests done with your doctor.


Give Yourself a Winning Edge

Whether your goal for 2016 is achieving a new personal best or finishing on top of the podium, make sure your vitamin D levels are adequate. Assess your vitamin D status, add more vitamin D-rich foods, and find the right supplement strategy to meet your needs.


Intense training requires a robust nutrition plan to meet your body’s demands, and failing to adequately replenish vitamin D can negatively impact too many key systems to ignore. Get your daily dose of vitamin D this winter. The research shows it can make all the difference.


Learn More About the Benefits of Vitamin D:



1. Farrokhyar F, et al., “Prevalence of vitamin D inadequacy in athletes: A systematic review and meta-analysis,” Sport Medicine 5 (2014): 365–78.

2. Willis KS, Smith DT, Broughton KS, Larson-Meyer DE. “Vitamin D status and biomarkers of inflmmation in runners,” Journal of Sports Medicine, 3 (2012): 35-42.

3. Ogan D, Pritchett K. “Vitamin D and the athlete: Risks, recommendations, and benefits,” Nutrients 5 (2013): 1856–1868.

4. Dahlquist D et al. “Plausible ergogenic effects of vitamin D on athletic performance and recovery,” Journal of the International Society of Sports Nutrition, 12 (2015):33

5. Koundourakis N et al. “Relation of vitamin D level to maximal oxygen uptake in adults,” American Journal of Cardiology, 107 (2011):1246–9.

6. Forney L, et al. “Vitamin D status, body composition, and fitness measures in college-aged students,” Journal of Strength and Conditioning Research, 28 (2014): 814–24.

7. Jastrzębski Z. “Effect of vitamin D supplementation on the level of physical fitness and blood parameters of rowers during the 8-week high intensity training,” Facicula Educ Fiz şi Sport, 2 (2014): 57–67.

8. Close G et al. “Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function,” Journal of Sports Science, 31 (2013): 344–53.

9. Wehr et al. “Association of vitamin D status with serum androgen levels in men,” Clinical Endocrinology (Oxf), 73 (2010): 243–8.

10. Pilz S, et al. “Effect of vitamin D supplementation on testosterone levels in men,” Hormone and Metabolic Research, 43 (2011): 223–5.

11. Barker T et al. "Supplemental vitamin D enhances the recovery in peak isometric force shortly after intense exercise," Nutr Metab (Lond), 10 (2013): 69.

12. Youssef D et al. “Vitamin D’s potential to reduce the risk of hospital-acquired infections,” Dermatoendocrinol, 4(2012):167-75.

13. Larson E. “Vitamin D supplementation in athletes,” Nestle Nutrition Institute Workshop Series, 75 (2013): 109-21.

14. Polak M et al. “Serum 25-hydroxyvitamin D concentrations and depressive symptoms among young adult men and women,” Nutrients, 6 (2014): 4720–30.


Photo 1 courtesy of CrossFit, Inc.

Teaser photo and Photo 2 courtesy of Jorge Huerta Photography.