The Sunshine Vitamin: Vitamin D and Athletes

March 08, 2019

Vitamin D has gotten its fair share of attention from sports science researchers in the last decade. Although vitamin D is an organic compound that can be found in some (albeit, very limited) foods, requirements in humans can be met entirely through exposure to UVB rays and synthesis through the skin, which is why it’s been coined as “the sunshine vitamin”. The role of vitamin D in the maintenance of bone and skeletal health through calcium and phosphorus metabolism is well documented. The latest research on vitamin D in athletes also points to its role in non-skeletal functions such as skeletal muscle growth, inflammatory modulation and immunity. The need for certain micronutrients such as vitamin D, calcium and iron may also be increased in athletes due to the metabolic stress of training as well as muscle adaptations. Conclusions from current evidence show that insufficient levels of vitamin D may negatively affect athletic performance.

Blood vitamin D (serum 25(OH)D) is the best indicator of vitamin D status. A large survey showed that over 30% of Canadians have insufficient circulating levels of vitamin D. Additionally, data shows that athletes in most countries do not come close to meeting the minimum dietary recommendations.

 

Table -1 Vitamin D status

Status

Circulating 25(OH)D

Deficient

<50nmol/L (20ng/mL)

Insufficient

<75-80nmol/L (30-32ng/mL)

Sufficient

>75-80nmol/L (30-32ng/mL)

Optimal

<100-250nmol/L (40-100ng/mL)

Toxic

>375nmol/L (>150ng/mL)


Several factors may influence vitamin D status in athletes, including:

  • Poor or restrictive diets;
  • Training primarily indoors;
  • Sun avoidance, limited sun exposure, wearing UVB protective clothing and/or regular use of sunscreen;
  • Environmental factors (ex. pollution);
  • Darker skin pigmentation;
  • Older athletes > 70 years old (synthesis is reduced with age);
  • Geographical location and time of year - wintertime latitude >35° north or south of the equator (pink and blue zones on the map below). 

vitamin D latitude globe zones

Dietary Sources

The recommended intake of vitamin D for healthy adults is 600 IU/day (USA & Canada, Institute of Medicine). Vitamin D is found in small amounts in a limited number of natural and fortified foods, which makes it very hard to reach the recommended intake through food alone.

 Table -2 Vitamin D in foods

Food

IU/serving*

Salmon (100g cooked)

275 IU

Fortified milk (250 mL)

100 IU

Egg yolk, large (1)

30 IU

Margarine (1 tsp/5 mL)

20 IU

*Canadian Nutrient File database.
IU: international units. 1000 IU = 25 micrograms.

 

As a general recommendation, a combination of sun exposure, dietary intake and supplementation can help keep you on the right track:

  1. Sunshine: Although it is difficult to estimate the amount of vitamin D obtained from sunlight due to the individual variability, sensible sun exposure on bare skin (arms, legs, back) for 5-30 minutes several days a week should expose you to enough UVB.
  2. Diet: Try to include vitamin D containing foods regularly in your meal planning.
  3. Supplementation: As needed, take a vitamin D supplement containing 600-1000 IU/day (available over the counter). Supplementation in winter is recommended for all athletes living/training at >35° north or south (in Canada, this is generally from October thru April).

 

It is important to note that there is no ergogenic effect of providing doses of supplemental vitamin D above the recommended levels.

If you are unsure about your vitamin D status, have a history of stress fracture, frequent illness, bone and joint injury, skeletal pain or weakness, or signs of overtraining, talk to your health care professional about having your vitamin D levels checked and individualized guidance on acceptable levels of vitamin D intake.

 

Written by:

Stephanie Jamain, M.Sc, RD, CSSD
Sports Nutritionist

 

References:

Larson-Meyer, E. The Importance of Vitamin D for Athletes. Sports Science Exchange (2015) Vol. 28, No. 148, 1-6.

Owens DJ et al. Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Med (2018) 48 (Suppl 1):S3–S16.

Statistics Canada. (2013) Vitamin D Blood Levels of Canadians.