Will drinking your milk daily provide you with the cardio fitness of a marathon runner? Probably not. However, new study data from investigators at the Virginia Commonwealth University (VCU) links vitamin D levels to cardiorespiratory fitness. While it is well established that vitamin D is important for healthy bones, there is a growing body of evidence that suggests it plays a significant role in other areas of the body including the heart and muscles.

“Our study shows that higher levels of vitamin D are associated with better exercise capacity,” explains lead study investigator Amr Marawan, M.D., assistant professor of internal medicine at VCU. “We also know from previous research that vitamin D has positive effects on the heart and bones. Make sure your vitamin D levels are normal to high. You can do this with diet, supplements, and a sensible amount of sun exposure.”

Cardiorespiratory fitness, a reliable surrogate for physical fitness, is the ability of the heart and lungs to supply oxygen to the muscles during exercise. It is best measured as the maximal oxygen consumption during exercise, referred to as VO2 max. People with higher cardiorespiratory fitness are healthier and live longer.

Findings from this new study were published in the European Journal of Preventive Cardiology through an article titled “Association between serum vitamin D levels and cardiorespiratory fitness in the adult population of the USA.” This study investigated whether people with higher levels of vitamin D in the blood have improved cardiorespiratory fitness. The study was conducted in a representative sample of the U.S. population aged 20–49 years using the National Health and Nutrition Survey (NHANES) in 2001-2004. Data was collected on serum vitamin D and VO2 max. Participants were divided into quartiles of vitamin D levels.

The current study tracked 1,995 participants, 45% were women, 49% were white, 13% had hypertension, and 4% had diabetes. Participants in the top quartile of vitamin D had a 4.3-fold higher cardiorespiratory fitness than those in the bottom quartile. The link remained significant, with a 2.9-fold strength, after adjusting for factors that could influence the association such as age, sex, race, body mass index, smoking, hypertension, and diabetes.

“The relationship between higher vitamin D levels and better exercise capacity holds 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,” Dr. Marawan notes.

Interestingly, each 10 nmol/L increase in vitamin D was associated with a statistically significant 0.78 mL/kg/min increase in VO2 max. “This suggests that there is a dose-response relationship, with each rise in vitamin D associated with a rise in exercise capacity,” Dr. Marawan states.

However, since vitamin D toxicity can lead to excess calcium in the blood, Dr. Marawan stresses that “it is not the case that the more vitamin D, the better. Toxicity is caused by megadoses of supplements rather than diet or sun exposure, so caution is needed when taking tablets.”

Moreover, the researchers pointed out that this was an observational study and it cannot be concluded that vitamin D improves exercise capacity—yet, “the association was strong, incremental, and consistent across groups,” Dr. Marawan remarks. “This suggests that there is a robust connection and provides further impetus for having adequate vitamin D levels, which is particularly challenging in cold, cloudy places where people are less exposed to the sun.”

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