Marwan et al. investigated the association of cardiorespiratory fitness (CRF) and serum levels of vitamin D in 1995 participants ranging from 20-49 years of age. CRF refers to the ability of mitochondria in the body to utilize atmospheric oxygen and reflects the efficiency of the heart, lung, and muscle cells to extract oxygen.
Prior studies have shown that low CRF is a strong and independent risk factor for stroke, lung cancer, diabetes, and cardiovascular disease.
Participants were arranged in 4 groups to investigate the relationship between serum vitamin D levels and V02 max. As serum vitamin D increased so did V02 max indicating a potential increase in CRF.
When you look at all of the data collected in the study BMI a basic measure of height to weight ratio also decreased in each group. The number of participants with the highest serum vitamin D levels also had the lowest incidence of high blood pressure.
Further limitations of the study include vitamin D intake (dietary or supplement) was NOT collected. Physical exercise was also NOT considered, which is well known for improving CRF.
In short, while this study provides some interesting information it’s largely correlational. It can't be said vitamin D is truly the cause for improved CRF. It may be body weight, physical activity and/or overall lifestyle.
This study does, however, open up a conversation around further studies on the effects of vitamin D and performance.
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