A study with 90 young women aged between 16 and 22 found that almost 60 per cent were vitamin D insufficient, and that muscle fat levels were higher in these women, compared with women with normal vitamin D levels, according to findings published in the Journal of Clinical Endocrinology and Metabolism.​

The findings are said to be the first to show a clear link between Vitamin D levels and the accumulation of fat in muscle tissue, and add to an ever growing body of science supporting the benefits of maintaining healthy vitamin D levels.

In adults, it is said vitamin D deficiency may precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.

“Obviously this subject requires more study,”​ said lead researcher, Dr Richard Kremer from McGill University in Canada. “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 interventions. We need to take things one step at a time.”​

Study details​

In collaboration with Dr Vincente Gilsanz from the University of Southern California, the McGill researchers recruited the young Californian women and measured blood levels of 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form of the vitamin, as well as levels of fat, muscle mass, and percent muscle fat.

Results showed that almost 60 per cent of the women had insufficient levels, equivalent to blood levels lower than 29 nanograms per millilitre, of which 24 per cent were classed as vitamin D deficient (levels below 20 ng/ml).

Vitamin D levels were found to be strongly linked to the percent of fat in muscle, with lower D levels resulting in higher fat content.

“This reciprocal association between vitamin D status and muscle fat was not previously reported and is unexplained and intriguing,”​ wrote the researchers in the JECM.

The researchers noted surprise at their findings since the women were all healthy young women living in California, with adequate exposure to sunshine.

“We are not yet sure what is causing vitamin D insufficiency in this group,”​ said Dr Kremer. “High levels of vitamin D could help reduce body fat. Or, fat tissues might absorb or retain vitamin D, so that people with more fat are likely to also be vitamin D deficient.”​

This study was funded by a grant from the National Institutes of Health, the U.S, Department of the Army, the Canadian Institutes of Health Research (CIHR), the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Dimensional Fund Advisors Canada Inc.

Data on D​

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.

While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.

Source: Journal of Clinical Endocrinology and Metabolism​

Published online ahead of print, doi:doi:10.1210/jc.2009-2309

“Vitamin D Status and Its Relation to Muscle Mass and Muscle Fat in Young Women”​

Authors: V. Gilsanz, A. Kremer, A.O. Mo, T.A.L. Wren, R. Kremer