by Doug Dupont
Many athletes are deficient in vitamin D, which is important for bone health and metabolism. However, until a recent study in the Journal of Strength and Conditioning Research, a comprehensive assessment of vitamin D status on numerous health and athletic factors in a single population had not occurred.
The chemical the researchers studied is called 25-hydroxyvitamin D, otherwise known as 25OHD. 25OHD is a metabolite of vitamin D, which means that vitamin D can turn into it after being utilized. In this case, the metabolites of vitamin D tell us about how it is being utilized, and analyzing 25OHD levels is the standard method of testing for vitamin D deficiency.
Interestingly, the researchers found that out of the 39 participants, only one person was taking a multivitamin. Even more interesting was the fact that this individual still tested low for 25OHD. The vitamin D content of the multivitamin was not disclosed, but it appears that the user had a vitamin D level of 400 IU, which is two-thirds of the recommended daily value.
The time of year and melanin levels of the participants were also taken into account. Most of the subjects were white, with three Hispanic participants. Lighter skin contains less melanin, which means that less exposure to the sun is required to achieve endogenous (produced naturally in the body) vitamin D. The study was also conducted in the summer time, and the participants were assessed for how often they went outside. Oddly, there was no correlation between sun exposure and vitamin D status, although this could be because of low precision on the collecting of this particular set of data.
The researchers also compared 25OHD status to a host of fitness and health factors. These included body fat, VO2 max, lower body power, and strength. Strength measurements were based on performance on the bench press, upright row, and leg flexion and extension exercises. Amongst these tests, vitamin D levels were significantly associated with two of the factors: VO2 max and BMI. High vitamin D was associated favorably with both, meaning that the higher the 25OHD levels were, the higher the VO2max was and the lower the BMI.
There are a few take-away points to this study. Vitamin D deficiency or insufficiency is more common than you might think. The researchers noted that at least forty percent of athletes may have insufficient levels of vitamin D for optimal health. When insufficiency occurs, it seems to associated with reduced cardiovascular and metabolic health. To prevent this, be sure to consume adequate vitamin D in your diet, and also spend plenty of time outside getting sun.