Researchers compared the vitamin D levels and cardiorespiratory fitness levels(how efficiently the heart and lungs supply oxygen to the muscles during exercise) in nearly 2,000 adults across the US.
They found that the participants in the top quartile of vitamin D had 4.3 times higher cardiorespiratory fitness levels than those in the bottom quartile. This meant they could work out harder and for longer than their peers.
“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,” explained Dr Amr Marawan, an assistant professor of internal medicine at Virginia Commonwealth University.
“The association was strong, incremental and consistent across groups. 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.”
As for the reason why, the authors noted a few contributing factors: firstly, the nutrient boosts the production of muscle protein and aids in the transportation of calcium and phosphorus on a cellular level. In addition, vitamin D may affect the body’s makeup of fast-twitch muscle fibres, which can “improve aerobic fitness.”
It’s worth tabling, however, that the study was observational and didn’t show a cause-and-effect relationship. Which means that while it’s possible that having high vitamin D improves fitness levels, it could merely be that a person with high fitness levels simply spends more time exercising outdoors – and is higher in vitamin D as a result.
This article originally appeared on Women’s Health.