Female resting with intense workout

When planning a nutritional strategy for building muscle strength, power, and force, most athletes think of protein and carbohydrates – not vitamin D. But emerging science is beginning to show exactly how important vitamin D is for muscle function.

According to a recent meta-analysis published in the Journal of Science and Medicine in Sport, vitamin D supplementation increases muscle strength (1). This latest study joins a slew of studies published over the last few decades suggesting that the “sunshine vitamin” plays an important role in optimising muscle strength, size, power, and function (2-5).Previous studies have found that people with severe vitamin D deficiency exhibited muscle weakness (3) and muscle wasting (6) that was improved by vitamin D supplementation (7,8). Athletes training to improve strength, speed, and explosive power should be particularly concerned about their vitamin D status because falling short of needs has been shown to specifically effect fast twitch muscle fibers (7).

Vitamin D, Type II Muscle Fibers, and Athletic Performance

Muscle is made of a mixture of two types of individual fibers: fast twitch fibers (type II fibers) and slow twitch fibers (type I fibers). Fast twitch fibers largely control speed and strength, whereas slow twitch fibers control endurance. Activities such as sprinting or heavy weight lifting that require short, powerful movements and bursts of energy rely greatly on fast twitch fibers. Reflecting this, elite sprinters have a higher percentage of fast twitch muscle fibers, while elite marathoners or long-distance runners have a higher percentage of slow twitch fibers.

Scientists aren’t sure of the mechanism behind vitamin D supplementation and muscle strength improvements. It’s unclear whether fast twitch fibers are increasing because new fibers are being synthesised or because slow twitch fibers are being converted into fast twitch fibers (7). What is clear, however, is that more larger and stronger type II fibers leads to faster sprint times, higher vertical leaps, and stronger Olympic lifts.

Every Athlete Should Supplement with Vitamin D

Athletes are always looking to gain a competitive edge, but frequently fall short when it comes to nutrition, especially when it comes to micronutrients such as vitamin D. The number of athletes failing to meet vitamin D needs has recently shown to be as high as 56 percent (10). Getting adequate amounts of vitamin D is an easy way athletes can make sure they perform at their best.

Although vitamin D can be made by the body following sun exposure, most athletes cannot rely on the sun to meet 100 percent of their vitamin D needs. For example, athletes who train indoors, outdoor in the early morning or evening, or who live in cooler regions of the country are very unlikely to obtain sufficient vitamin D from sun exposure alone. This lack of vitamin D synthesis from the sun is exacerbated even more during the winter season.

That’s why it’s critical that attention be paid to dietary intake of vitamin D. IsaLean and IsaLean PRO shakes provide 80 percent and 60 percent of the daily recommended intake for vitamin D, respectively, and one serving of Ageless Actives contains 250 percent of the daily recommended intake, an amount supported by science to be safe and effective.

Implementing a nutritional regimen that includes Isagenix IsaLean shakes and Ageless Actives is a foolproof way to meet Vitamin D needs while optimally supporting athletic performance.


  1. Tomlinson PB, Joseph C, Angioi M. Effects of vitamin D supplementation on upper and lower body muscle strength levels in healthy individuals. A systematic review with meta-analysis. J Sci Med Sport. 2014 Aug 11.
  2. McCarthy EK, Kiely M. Vitamin D and muscle strength throughout the life course: a review of epidemiological and intervention studies. J Hum Nutr Diet. 2014 Oct 3.
  3. Girgis CM et al. The roles of vitamin D in skeletal muscle: form, function, and metabolism. Endocr Rev. 2013 Feb;34(1):33-83.
  4. Moran DS et al. Vitamin d and physical performance. Sports Med. 2013 Jul;43(7):601-11.
  5. Hamilton B. Vitamin D and human skeletal muscle. Scand J Med Sci Sports. 2010 Apr;20(2):182-90.
  6. Boland R. Role of vitamin D in skeletal muscle function. Endocrine Reviews, vol. 7, no. 4, pp. 434–448, 1986.
  7. Ceglia L. Vitamin D and its role in skeletal muscle. Current Opinion in Clinical Nutrition and Metabolic Care. 2009;12(6):628–633.
  8. Sorensen OH et al. Myopathy in bone loss of ageing: improvement by treatment with 1 alpha-hydroxycholecalciferol and calcium. Clin Sci (Lond) 1979;56:157–161.
  9. Sato Y, Iwamoto J, Kanoko T, Satoh K. Low-dose vitamin D prevents muscular atrophy and reduces falls and hip fractures in women after stroke: a randomised controlled trial. Cerebrovasc Dis. 2005;20:187–192.
  10. Farrokhyar F et al. Prevalence of Vitamin D Inadequacy in Athletes: A Systematic-Review and Meta-Analysis. Sports Med. 2014 Oct 3.