A daily dose of 4,000 International Units (IU) of vitamin D for 12 weeks in combination with resistance training led to a significant decrease in the waist-to-hip ratio, which could be linked to decreased risks of type-2 diabetes, the metabolic syndrome, and cardiovascular disease.
“Therefore, the greater decrease in waist circumference associated with higher vitamin D intake represents a potential reduction in risk for metabolic disease and cardiovascular risk,” wrote researchers from Purdue University in the journal Clinical Nutrition.
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.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine (UV-B radiation with a wavelength between 290 and 315 nm), 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.
It has also been reported that people with higher levels of body fat require higher doses of vitamin D because 25(OH)D is sequestered by fat tissue.
For the new study, Dr Dorothy Teegarden and her co-workers recruited 23 overweight and obese people to participate in their double-blind, placebo-controlled trial. The recruits were randomly assigned to receive either vitamin D (4,000 IU) or placebo for 12 weeks in combination in with resistance training.
“The results of the current study demonstrated that vitamin D supplementation improved muscular power in healthy overweight and obese individuals within four weeks and that elevated vitamin D status was associated with greater losses in waist circumference, with no additional benefits in lean mass accumulation, muscular strength, or glucose tolerance during participation in a 12 week resistance exercise training program,” wrote Dr Teegarden and her co-workers.
Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2012.08.014
“Impact of vitamin D supplementation during a resistance training intervention on body composition, muscle function, and glucose tolerance in overweight and obese adults”
Authors: A.E. Carrillo, M.G. Flynn, C. Pinkston, M.M. Markofski, Y. Jiang, S.S. Donkin, D. Teegarden