There's an epidemic（流行病，传染病） in progress, and it has nothing to do with the flu. A ground-breaking study published in the March 2010 Journal of Clinical Endocrinology and Metabolism¹ found an astonishing 59 percent of study subjects had too little Vitamin D in their blood. Nearly a quarter of the group had serious deficiencies（缺乏，不足） (less than 20 ng/ml) of this important vitamin. Since Vitamin D insufficiency is linked to increased body fat, decreased muscle strength and a range of disorders², this is a serious health issue. "Vitamin D insufficiency is a risk factor for other diseases," explains principal investigator³, Dr. Richard Kremer, co-director of the Musculoskeletal Axis⁴ of the Research Institute of the MUHC. "Because it is linked to increased body fat, it may affect many different parts of the body. Abnormal（反常的，变态的） levels of Vitamin D are associated with a whole spectrum⁵ of diseases, including cancer, osteoporosis（骨质疏松症） and diabetes⁶（糖尿病） , as well as cardiovascular（心血管的） and autoimmune（自身免疫的） disorders."

The study by Dr. Kremer and co-investigator Dr. Vincente Gilsanz, head of musculoskeletal（肌骨骼的） imaging at the Children's Hospital Los Angeles of the University of Southern California, is the first to show a clear link between Vitamin D levels and the accumulation of fat in muscle tissue – a factor in muscle strength and overall health. Scientists have known for years that Vitamin D is essential for muscle strength. Studies in the elderly have showed bedridden（卧床不起的） patients quickly gain strength when given Vitamin D.

The study results are especially surprising, because study subjects – all healthy young women living in California – could logically be expected to benefit from good diet, outdoor activities and ample（丰富的，足够的） exposure to sunshine – the trigger that causes the body to produce Vitamin D.

"We are not yet sure what is causing Vitamin D insufficiency in this group," says Dr. Kremer who is also Professor of Medicine at McGill University. High levels of Vitamin D could help reduce body fat. Or, fat tissues might absorb（吸收） or retain Vitamin D, so that people with more fat are likely to also be Vitamin D deficient⁷."

The results extend those of an earlier study by Dr. Kremer and Dr. Gilsanz, which linked low levels of Vitamin D to increased visceral fat（内脏脂肪） in a young population. "In the present study, we found an inverse⁸（相反的，倒转的） relationship between Vitamin D and muscle fat," Dr. Kremer says. "The lower the levels of Vitamin D the more fat in subjects' muscles."

While study results may inspire some people to start taking Vitamin D supplements, Dr. Kremer recommends caution. "Obviously this subject requires more study," he says. "We don't yet know whether Vitamin D supplementation would actually result in less accumulation of fat in the muscles or increase muscle strength. We need more research before we can recommend interventions⁹. We need to take things one step at a time."