The Role of Vitamin D in Your Body and Your Muscles

The Role of Vitamin D in Your Body and Your Muscles
July 8, 2013 No Comments » Healthy Lifestyle Brian Fulton


Vitamin D is a fat-soluble vitamin which is responsible for enhancing intestinal absorption of calcium and phosphate and is therefore plays and extremely important role in calcium regulation and bone health. Emerging literature indicates vitamin D’s central role in other vital body processes, such as: signalling gene response, protein synthesis, hormone synthesis, immune response, as well as cell turnover and regeneration. Recent discovery of the vitamin D receptor within the muscle has suggested a significant role for vitamin D in muscle tissue function.


Vitamin D and your Muscles

Two studies looked at vitamin D’s role in muscle health[i][ii]. They found that reduced vitamin D levels had a significant effect on muscle weakness, pain, balance and fractures in aging individuals. Several observational studies have suggested that vitamin D status influences muscular strength and function in the elderly.[iii] [iv] It has been suggested that vitamin D supplementation in individuals with low vitamin D status may improve muscle strength. This is believed to be due to an increase in the size and amount of type II (fast twitch) muscle fibres associated with vitamin D supplementation. It should be noted that type II fibres are predominant in power and anaerobic activities, and are recruited first to prevent falls, associated with muscle strength in the aging population. These findings in regard to muscle tissue and function suggest that vitamin D status may have a significant effect on muscle performance and injury prevention.[v]

Sources of Vitamin D

Although the sun is the most plentiful source of vitamin D, there are also some dietary sources. Some common foods contain significant levels of vitamin D, naturally, including salmon, fatty fish, egg yolks, plus, fortified products also exist, such as, milk, cereal and orange juice. While these dietary sources may appear significant, the process of absorbing dietary vitamin D is only about 50% efficient; therefore, much of the nutrient value is lost in digestion. The lack of dietary vitamin D is yet another factor that increases the risk of vitamin D insufficiency. Most experts agree that a higher intake of vitamin D, through dietary sources, ultraviolet B (UVB) exposure, and supplementation, is necessary to obtain optimal serum vitamin D levels.



Deficiency of this vitamin is serious and according to current data[vi], up to 77% of North Americans are vitamin D deficient. Deficiency of this vitamin is implicated in:

Bone health– Low serum levels of vitamin D are associated with Osteomalacia (softening of the bones in adults), Rickets (osteomalacia in children), osteopenia and osteoporosis (reduction in bone density). Osteomalacia results from a defect in the bone-building process, while osteoporosis develops due to a weakening of previously constructed bone. Both involve vitamin D and calcium. One other bone-related factoid worth mentioning is that low vitamin D levels have been associated with falls in the elderly. It is well recognized that maintaining proper levels of vitamin D helps optimize bone health and prevents stress fractures.

Mortality- Low blood levels of vitamin D are associated with increased mortality. Giving supplementary vitamin D3 to elderly women in institutional care seems to decrease the risk of death.

Cancer- Low vitamin D levels are associated with a higher death rate in some cancers but it is not known whether low vitamin D status increases mortality from cancer or is just a consequence of poorer general health caused by cancer. Studies into the possible effect of vitamin D supplementation on the survival of cancer patients produce contradictory and inconclusive results. The currently available evidence is insufficient to recommend vitamin D supplementation in cancer patients.

Immune system- In general, vitamin D functions to activate our innate and immune system.Vitamin D deficiency has been linked to increased risk of viral infections. It has been postulated to play a role in influenza with lack of vitamin D synthesis during the winter as one explanation for high rates of influenza infection during the winter. Low levels of vitamin D appear to be a risk factor for tuberculosis, and historically it was used as a treatment. Vitamin D may also play a role in HIV.

Multiple sclerosis- Low levels of vitamin D are associated with multiple sclerosis. Supplementation with vitamin D may have a protective effect, but there are uncertainties and unanswered questions.

Pregnancy- Low levels of vitamin D in pregnancy are associated with gestational diabetes, pre-eclampsia, and small infants. The benefit of supplements, however, is unclear. Pregnant women who take an adequate amount of vitamin D during gestation may experience positive immune effects.



Optimal vitamin blood serum levels, dosage, deficiency, and insufficiency are always up for debate. It is hard to get clear consensus on most minerals or vitamins. I will give you three sources for vitamin D.  In November of 2010, the Institute of Medicine (IOM) released new recommendations for dietary intake of vitamin D, 400–600 IU/day for children & adults (0–70 years), 800 IU/day for older adults (>70 years). The Endocrine Society of America recommends 400–1000 IU/day for infants, 600–1000 IU/day in children (1–18 years) and 1500–2000 IU/day in adults, in addition to sensible sun exposure.

National Institute of Medicine

Age Recommended Intake (IU/day) Upper Limit (IU/day)
Children (0–18 years) 400–600 2500 (1–3 years)3000 (4–8 years)4000 (13–18 years)
Adults (19–70 years) 600 4000
Older Adults (>70 years) 800 4000
Pregnancy/Lactation 600 4000
The Endocrine Society
Children (0–18 years) 400–1000 2000–4000
Adults (19–70 years) 1500–2000 10,000
Older Adults (>70 years) 1500–2000 10,000
Pregnancy/Lactation 600–1000 (14–18 years)1500–2000 (19–50 years) 10,000
Overdosing- Toxicity

The tolerable upper limit for vitamin D has been set by the IOM at 4000 IU for adults, compared to 10,000 IU/day by the Endocrine Society. Leading experts have claimed that a daily intake of 10,000 IU would take months, or even years to manifest symptoms of toxicity. A 2010 publication found no cases of toxicity with daily intakes of 30,000 IU per day for an extended period of time[vii]. Regardless of the current dietary intake value, the amount of vitamin D produced from 15 min of unprotected sun exposure is 10,000 to 20,000 IU, in a light-skinned individual, making most experts believe toxicity to be a rare and unlikely event.

For more information on Vitamin D and cancer prevention go to Vitamin D – It turns out that we all need more.

For a current review of the evidence, go to to see Dr. Greger’s six-part video series on vitamin D.

*Note- This site does not provide medical advice. All information provided is for informational purposes only. Before making changes, speak to your primary health care provider.

[i] Campbell, P.M.F.; Allain, T.J. Muscle strength and vitamin D in older people. Gerontology 2006, 52, 335–338.

[ii] Ceglia, L. Vitamin D and skeletal muscle tissue and function. Mole Aspects Med. 2008, 29, 407–414.

[iii] Ceglia, L.; Harris, S.S. Vitamin D and its role in skeletal muscle. Calcif. Tissue Int. 2013, 92, 151–162.

[iv]Bischoff-Ferrari, H.A.; Dietrich, T.; Orav, E.J.; Hu, F.B.; Zhang, Y.; Karison, E.W.; Dawson-Hughes, B. Higher 25-hydroxyvitamin D concentrations are associated with better lower-extremity function in both active and inactive persons aged > or =60 y. Am. J. Clin. Nutr. 2004, 80, 752–758.

[v] Ogan, D. : Pritchett, K.  Vitamin D and the Athlete: Risks, Recommendations, and Benefits.  Nutrients 2013, 5, 1856-1868

[vi] Ogan, D. : Pritchett, K.  Vitamin D and the Athlete: Risks, Recommendations, and Benefits.  Nutrients 2013, 5, 1856-1868

[vii]Heaney, R.P. Vitamin D in health and disease. Clin. J. Am. Soc. Nephrol. 2008, 3, 1535–1541.



About The Author
Brian Fulton Brian Fulton has been a Massage Therapist in Ontario Canada since 1999. His approach toward health and the human body is broad and holistic in nature. Brian is also the author of The Placebo Effect in Manual Therapy: Improving Clinical Outcomes (available on Amazon)