The study was designed to assess the effects of vitamin D supplementation during exercise training on body composition, muscle function, and glucose tolerance. The investigators hypothesis for these studies is that vitamin D supplementation enhances exercise-induced increases in strength and lean mass, potentially through enhancing insulin sensitivity and reducing inflammation.

The study was designed to assess the effects of vitamin D supplementation during exercise training on body composition, muscle function, and glucose tolerance. It was a double-blind, randomized, placebo-controlled, clinical trial with participants randomized into either a 4,000 IU/day vitamin D or placebo group and all participants completed 12 wks (3 d/wk) of exercise training.

Inclusion Criteria:

• Physical activity scores in the "low" to "very low" category
• Fitness estimations in the "below average" or lower categories
• body mass index scores >24.9 indicating overweight or obesity.

Exclusion Criteria:

• Use of tanning booths or other artificial UV light exposure
• High baseline vitamin D and calcium intake
• Plans to visit sunny/warm destinations during the winter months/study period
• History or presence of metabolic disease, type 2 diabetes, eating disorders, gastrointestinal disorders, pregnancy or lactation
• Use of drugs to treat obesity (last 12 weeks)
• Use of over the counter anti-obesity agents (last 12 weeks)
• Recent initiation of an exercise program (last four weeks).