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 reduce 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 sun light 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.