Vitamin D: The Endurance Vitamin – Part 1

All vitamins are essential but one, vitamin D may be particularly important for endurance athletes. Vitamin D is best known for its role in building healthy bones. Vitamin D is essential for calcium absorption. However a number of studies have shown that vitamin D plays an important role in enhancing endurance performance. For example:

• Vitamin D has been shown to increase protein synthesis, improve muscle mass and body mass

• Vitamin D deficiency results in a decrease in energy production in the mitochondria, the cell's energy factory

• Vitamin D deficiency is associated with reduced cardiac function and increased heart rate. Increased heart rate during exercise causes fatigue and a reduction in endurance performance

Other evidence supporting the role of Vitamin D in endurance performance is what researchers term the seasonality of physical fitness. Vitamin D is converted by sunlight to its active form. Thus when exposure to sunlight is consistent there is little need for Vitamin D supplementation. Thus one would expect Vitamin D levels to fall in the winter for athletes in northern climates. This is what is seen and this decrease is paralleled with a decrease in physical performance. Other studies have shown that physical fitness and tolerance to hypoxia is highest in the summer and declines starting in the fall.

The bottom line, pay attention to your vitamin D levels going into the winter months. It is probably worthwhile to take a vitamin D supplement particularly if you are training indoors.

Vitamin D: The Endurance Vitamin - Part 2

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 cardiorespiratory fitness. What makes this research compelling is the investigators analyzed vitamin D levels in almost 2000 subjects including men and women. The mean age was 33 years. Researchers measured cardiorespiratory fitness or VO2 max. VO2 max is a measure of the ability of the mitochondria to utilize oxygen and reflects the 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.