Vitamin D has been shown to be critical to the absorption of calcium to the body. This means it is highly important to develop good bone density, especially in young children and the elderly. This is where Vitamin D started making its name.
More recently, Vitamin D has been linked to a much broader range of benefits recently and is beginning to become known as the most important vitamin out there (vitamin C is way overrated). It has been shown that there is a strong link between Vitamin D deficiency and depression and seasonal affective disorder (SAD).
There are studies dating back to the 1930s that have shown Vitamin D to increase athletic performance in sprinters, cyclists, and weightlifters. These studies showed that Vitamin D affected not just muscle synthesis but also speed, reaction time, and endurance in the athlete.
Studies have also linked increased Vitamin D levels to overall health levels. Immune system function increased a Vitamin D levels increase, Parkinson’s and Alzheimer’s patients have been shown have low Vitamin D levels. Low D levels have also been linked to multiple forms of cancer, hypertension, heart disease, and diabetes. Although some of these links can be called into question via the “correlation is not causation” argument (for example, does having low levels of Vitamin D cause alzheimers or does alzheimers cause vitamin D levels to drop?), ultimately Vitamin D supplementation has been shown to significantly reduce mortality which is a good thing.