Vitamin D and Muscle Function
Vitamin D is a fat-soluble vitamin, which acts functionally as a hormone.¹ It promotes calcium absorption in the gut and helps to maintain adequate serum calcium levels in the blood. Vitamin D also plays a role in neuromuscular and immune function as well as in reducing inflammation.²
The main source of active vitamin D comes from exposure to ultraviolet B (UVB) radiation from sun exposure.¹ However, age, latitude, time of day, time of the year and skin pigmentation can impact the production of vitamin D in the skin.³ Recreational athletes at risk for vitamin D insufficiency/deficiency include those who exercise mostly indoors, have dark skin pigmentation, wear clothing that covers most or all of their body, live at latitudes >35 degrees north or south of the equator, often use sunscreen and/or suffer from disorders causing gastrointestinal malabsorption.¹
Inadequate levels of vitamin D may have significant long-term health impacts (i.e. may increase risk of colon cancer, diabetes) as well as more immediate effects on musculoskeletal health (i.e. increasing risk of injuries like stress fractures).⁴ Vitamin D deficiency has also been found to negatively impact muscle strength³
Over the past several years, it has been suggested that insufficient vitamin D levels may negatively affect performance in deficient athletes. Supplementing vitamin D in athletes with insufficient levels or encouraging higher intakes of vitamin D rich foods may have beneficial effects on an athlete’s strength, power, reaction time and balance.¹ʼ⁴ Vitamin D supplementation in deficient adults has been shown to improve tests of muscle performance and may have possible impacts on muscle fibre composition and morphology.² See below for vitamin D recommendations as well as the vitamin D content of common foods.
* It is not recommended that individuals over expose themselves to UVB radiation in an attempt to increase vitamin D levels as this can lead to sunburn and melanoma.
Vitamin D Recommendations:
|Age in years||Aim for an intake of||Stay below|
|Men and Women 19-50||600 IU||4000 IU|
|Men and Women 51-70||600 IU||4000 IU|
|Men and Women 71 and older||800 IU||4000 IU|
Table from Dietitians of Canada⁵
Vitamin D Content of Some Common Foods
|Food||Serving Size||Vitamin D (IU)|
|Orange juice, fortified with vitamin D||125 mL||50|
|Soy beverage, fortified with vitamin D||250 mL||123|
|Skim milk powdered||60 mL||103|
|Rice, oat, almond beverage, fortified with vitamin D||250 mL||88-90|
|Yogurt, fortified with vitamin D||175 mL||58-71|
|Egg yolk, cooked||2 large||57-88|
|Snapper, cooked||75 g||392|
|Mackerel, cooked||75 g||342|
Adapted from Dietitians of Canada⁵
Makes 6 servings.
- Combine white sugar, corn starch, cocoa, salt and skim milk powder in a medium, heavy saucepan; stir with a whisk.
- Gradually add low-fat milk and evaporated milk, stirring with a whisk.
- Bring to a boil over medium heat, stirring constantly with a whisk. Reduce heat, and simmer 1 minute or until thick.
- Remove from heat; add chocolate, stirring until melted and mixture is smooth.
- Stir in vanilla.
- Chill at least 4 hours before serving. Add garnish if desired.
Recipe adapted from: http://www.myrecipes.com/recipe/creamiest-chocolate-pudding
1) Vitamin D. Australian Institute of Sports Website. http://www.ausport.gov.au/__data/assets/pdf_file/0003/594174/CORP_33413_SSF_Vitamin_D_FS.pdf. Updated May 2014. Accessed March 13, 2016.
2) Ceglia L. Vitamin D and Its Role in Skeletal Muscle. Curr Opin CLin Nutr Metab Care. 2009;12(6):628-633.
3) Pfeifer M, Begerow B, Minne HW. Vitamin D and Muscle Function. Osteoporos Int. 2002;13(3):187-194.
4) Hamilton B. Vitamin D and Athletic Performance: The Potential Role of Muscle. Asian J Sports Med. 2011;2(4):211-219.
5) Food Sources of Vitamin D. Dietitians of Canada Website. http://www.dietitians.ca/getattachment/464f3006-0bb2-4f1a-a338-0b21d148bacb/Factsheet-Food-Sources-of-Vitamin-D.pdf.aspx. Published March 20, 2012. Updated 2014. Accessed March 8, 2016.