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Emerging Vitamin D Research: Immunity, Muscle Function

Emerging Areas of Vitamin D Research

As many as a billion people worldwide, including more than 30% of Americans, have low levels of vitamin D (1). Those figures are fairly stunning since insufficient blood levels of vitamin D may well contribute to a spectrum of health conditions such as osteoporosis, certain cancers, cardiovascular disease and diabetes. [See Staying Healthy newsletters March, 2010 and November, 2007].

The Institute of Medicine (IOM) has been conducting a review of the available vitamin D science, and is due to deliver its findings later this year. Many experts expect the IOM to recommend daily intakes much above the current levels of 400 IU.

In the meantime, researchers are delving deeper into the potential benefits of getting enough vitamin D, as well as how this vitamin works throughout the body. Two areas receiving attention are the role of vitamin D in the immune system and its possible contribution to maintaining strong, healthy muscles.

Promise Against Seasonal Flu

That vitamin D is involved in regulating the immune system is not a new idea. But researchers from the University of Copenhagen believe they have figured out how: it’s crucial for activating key immune defense cells. The Danish scientists report that vitamin D is necessary to trigger the action of T-cells (2) – the immune system’s killer cells. Too little vitamin D means these cells remain inactive and unable to mobilize against foreign invaders.

Researchers recently tested the effects of vitamin D in a placebo-controlled trial among 300+ school children in Japan (3). They found that supplemental doses of vitamin D reduced the incidence of seasonal flu (influenza A) by over 40% compared to the placebo group over the course of 4 months. The benefits were even more noticeable in children who had low levels of vitamin D at the start of the study.

Canada’s Public Health Agency also confirmed last year that it is partnering with universities and hospitals to find out whether there’s a correlation between severe seasonal flu and low vitamin D levels and/or a person’s genetic make-up. The bottom line is to continue getting seasonal flu shots and practice preventive hygiene. But it’s also a good idea to get adequate vitamin D for a healthy immune response.

Strong Muscles and Vitamin D Linked

A study by researchers from McGill University and University of Southern California is one of the first to show a clear link between vitamin D levels and the accumulation of fat in muscle tissue (4) – a factor in muscle strength and overall health. They found that the lower the levels of vitamin D the more unwanted fat was present in subjects' muscles.

A remarkable 59% of the study subjects had too little vitamin D in their blood, and nearly 25% of the group had serious deficiencies (less than 20 ng/ml). These results are surprising, because the subjects – all healthy young women living in California – could be expected to benefit from ample exposure to sunshine, the trigger that causes the body to produce vitamin D.

The authors of the study are not yet sure what’s causing vitamin D insufficiency in these women. Better levels of vitamin D might be helping to keep fat from infiltrating muscles. Or also it’s possible that in overweight people more vitamin D is retained in fat tissues leaving a shortage in blood.

Studies in the elderly, though, have led scientists to believe that vitamin D is essential for muscle strength. Older, bedridden patients, for example, have been shown to gain strength when given vitamin D. And a recent study reports that fatty degeneration of thigh muscles in elderly adults is associated with low levels of the vitamin in blood and poor balance and gait (5).

References

1. Fryhofer, SA. Vitamin D deciphered, declassified and defined for your patients. Internal Medicine, March 22, 2010.
2. vonEssen MR, et al. Vitamin D controls T cell antigen receptor signaling and activation of human T cells. Nature Immunology 11:344-9, 2010.
3. Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. American Journal of Clinical Nutrition 91:1255-60, 2010.
4. Gilsanz V, et al. Vitamin D Status and Its Relation to Muscle Mass and Muscle Fat in Young Women. Journal of Clinical Endocrinology & Metabolism 95:1595-601, 2010.
5. Tagliafico AS, et al. Relationship between fatty degeneration of thigh muscles and vitamin D status in the elderly: a preliminary MRI study. American Journal of Roentgenology 194:728-34, 2010.