Optimal vitamin D levels linked to improved exercise capacity
Vitamin D levels in the blood are linked to cardiorespiratory fitness, according to a new study from the USA. Participants in the top quartile of vitamin D had a 4.3-fold higher cardiorespiratory fitness than those in the bottom quartile.
Cardiorespiratory fitness is the ability of the heart and lungs to supply oxygen to the muscles during exercise and is a reliable surrogate for physical fitness. It is best measured as the maximal oxygen consumption during exercise (VO2 max). People with higher cardiorespiratory fitness are healthier and live longer.
Previous research shows that vitamin D has positive effects on the heart and bones – and current advice is to ensure that vitamin D levels are normal to high by maintaining a healthy diet, a sensible amount of sun exposure and vitamin supplements. This study was conducted in a representative sample of the US population aged 20–49 years using the National Health and Nutrition Survey (NHANES) in 2001–2004. Of 1995 participants, 45% were women, 49% were white, 13% had hypertension, and 4% had diabetes. Data was collected on serum vitamin D and VO2 max. Participants were divided into quartiles of vitamin D levels.
The relationship between higher vitamin D levels and better exercise capacity was seen in men and women, across the young and middle age groups, across ethnicities, regardless of body mass index or smoking status, and whether or not participants have hypertension or diabetes. The link between vitamin D level and VO2 max remained significant with a 2.9-fold strength after adjusting for all these factors. There was a dose response relationship with each 10 nmol/L increase in vitamin D associated with a statistically significant 0.78 mL/kg/min increase in VO2 max.
Although this was an observational study and it cannot be concluded that vitamin D improves exercise capacity, the association was strong and consistent across groups and suggests the need for adequate vitamin D levels, which is particularly difficult in environments where people are less exposed to the sun. However, it should be remembered that large doses of supplements can cause vitamin D toxicity leading to excess calcium in the blood, so caution is needed when taking tablets.
Although optimum vitamin D levels for healthy bones are known, further randomised controlled trials should be conducted to examine the impact of differing amounts of vitamin D supplements on cardiorespiratory fitness. From a public health perspective, research should look into whether supplementing food products with vitamin D provides additional benefits beyond bone health.
Marawan A, Kurbanova N, Qayyum R. Association between serum vitamin D levels and cardiorespiratory fitness in the adult population of the USA. European Journal of Preventive Cardiology. 2018. DOI: 10.1177/2047487318807279
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