VITAMIN D: The Endurance Vitamin – Part 2

VITAMIN D: The Endurance Vitamin – Part 1 discussed the role of Vitamin D on endurance performance. Normal levels of Vitamin D range from 20 to 50 ng/ml. However a recent study suggests that athletes who have Vitamin D at the upper range of normal have improved endurance performance. 
The study, reported by researchers at Virginia Commonwealth University, showed a direct relation between Vitamin D levels and cardio respiratory fitness. What makes this research compelling is the investigators analyzed Vitamin D levels in almost 2,000 subjects including men and women. The mean age was 33 years. Researchers measured cardio respiratory fitness or VO2 max.  VO2 max is a measure of the ability of the mitochondria to utilize oxygen and reflects efficiency of the heart, lung muscle cells to extract oxygen. VO2 max is directly correlated with greater endurance performance.
The researchers separated the subjects into three groups, high, medium and low, depending on their vitamin D levels. They found a strong association between Vitamin D levels and VO2 max. This association was independent of age, sex, race, BMI or other clinical conditions. One of the most fascinating aspects of this study is that for every increase in Vitamin D level there was a corresponding increase in VO2 max.
The researchers cautioned that athletes should not overdose on Vitamin D. Vitamin D toxicity can cause nausea, vomiting and weakness because it leads to an excess of calcium in the blood. Based on this study, endurance athletes might want to, particularly during the winter months when we lose the benefit of sunlight activation, ensure that their Vitamin D levels are at the upper range of normal (50 ng/ml). Vitamin D supplementation of 600 IU is certainly appropriate but diet is still the best approach. A three-ounce serving of salmon provides about 450 IU vitamin D.