For years, researchers have debated the benefits of vitamin D supplements. Now, finally, comes research from Newcastle University suggesting that the hormone that is naturally produced in the skin with help from sunlight can improve the aerobic function of our muscles, although perhaps only in people whose natural vitamin D levels are low. ScienceDaily reports that the researchers looked at phosphocreatine recovery times in patients with vitamin D deficiency, using a magnetic resonance scan to measure phosphocreatine dynamics in response to exercise in the calf muscles of 12 patients with severe vitamin D deficiency. The team found that phosphocreatine recovery significantly improved after the patients took oral vitamin D for 10-12 weeks. They also found that all patients reported an improvement in symptoms of fatigue after taking the supplement. Read more from ScienceDaily.