Effects of Vitamin D Supplementation in Obesity

Obesity is an increasing health problem with numerous metabolic complications. Vitamin D deficiency is common in obesity, and in epidemiological studies vitamin D deficiency has been linked to metabolic complications, such as type 2 diabetes, insulin resistance and cardiovascular disease, as well as myopathy, osteoporosis and depression. In obesity, a low grade inflammation is present in the fat tissue, thereby releasing inflammatory molecules to the blood stream. In cell line studies as well as small clinical studies vitamin D has been shown to have the ability to reduce inflammation and cell growth. In the present study the investigators wish to investigate the effect of vitamin D on fat-, muscle and bone metabolism. 30 healthy obese subjects will be treated with cholecalciferol 175 micrograms daily for 6 months and will be compared with 30 healthy obese subjects treated with placebo. The investigators hypothesize that restoring vitamin D levels in vitamin D deficient obese subject will reduce inflammation and thereby reduce obesity-related complications. The effect will be evaluated as follows: * Levels of circulating inflammatory markers will be examined in blood samples collected prior to and after treatment. * Effects on fat- and muscle metabolism will be evaluated in fat- and muscle samples taken before and after treatment. * Effects on fat distribution will be evaluated by MRI scan before and after treatment. * Effects on insulin sensitivity will be evaluated by hyperinsulinaemic euglycaemic clamp performed on a subgroup of subjects with impaired fasting glucose. * Effects on bone marrow density will be evaluated by DEXA scans before and after treatment. * Effects on quality of life and depression score will be evaluated by questionnaires used before and after treatment.