You already know that vitamin D is good for your bones, your brain, and your heart. Now, new research suggests that it may also give your workout routine a boost. According to a study published in the European Journal of Preventive Cardiology, people with higher levels of vitamin D tend to be more physically fit.
Specifically, the study looked at cardiorespiratory fitness, a measure of how efficiently the heart and lungs supply oxygen to the muscles during exercise. People with higher cardiorespiratory fitness can exercise longer and harder, and they also tend to live longer and healthier lives.
For the study, researchers compared the vitamin D levels and cardiorespiratory fitness levels—measured by a treadmill test—of nearly 2,000 U.S. adults ages 20 to 49 who took part in a nationwide study from 2001 to 2004.
They found that people in the top quartile of vitamin D had cardiorespiratory fitness levels that were 4.3 times higher than those in the bottom quartile. Each 10-point increase in vitamin D was associated with a 0.78-point increase in VO2 max, the measurement for cardiorespiratory fitness.
Even after adjusting for participants’ age, sex, race, body mass index, and health history, fitness levels for those with the highest vitamin D levels were still 2.9 times higher than those with the lowest. The link held true for both men and women, and for all of the age groups and ethnicities in the study. It was also true regardless of whether participants were smokers or had hypertension or diabetes.
The study was observational, so it could not show a cause-and-effect relationship. But the association was “strong, incremental, and consistent across groups,” said lead author Amr Marawan, MD, assistant professor of internal medicine at Virginia Commonwealth University, in a news release from the European Society of Cardiology (ESC).
“This suggests that there is a robust connection and provides further impetus for having adequate vitamin D levels,” Dr. Marawan said, “which is particularly challenging in cold, cloudy places where people are less exposed to the sun.”
Vitamin D is known as the sunshine vitamin because the human body makes vitamin D in response to sun exposure. People can also get it from supplements or from fortified foods. (The study did not take into account how much vitamin D participants got from sun, supplements, or food.)
The study notes that vitamin D could potentially affect cardiorespiratory fitness in several ways. For starters, the nutrient has been shown to boost the production of muscle protein and aid in calcium and phosphorus transport on a cellular level. It may also affect the body’s makeup of fast-twitch muscle fibers, “suggesting that vitamin D may improve aerobic fitness,” the authors wrote.
This isn’t the first study to suggest a link between vitamin D and athletic performance: Previous research has noted that vitamin D-deficient ballet dancers jump higher and have fewer injuries—and pro athletes have better sprint times—when they take supplements. Vitamin D levels have also been linked to levels of inflammation, pain, and weakness.
In the ESC news release, Dr. Marawan said the study is another good reason for people to make sure they’re getting enough vitamin D—which can be done through diet, supplements, and “a sensible amount of sun exposure.”
Stella Volpe, PhD, professor of nutrition sciences at Drexel University, agrees with Dr. Marawan. “The study was very well done,” she says, “and given what we know about vitamin D’s role in protein synthesis of muscle, these findings are really not a stretch at all.” (Volpe was not involved in the current study, but she has conducted other research on vitamin D and physical fitness.)
Volpe does point out, however, that the study only found a relationship between vitamin D and cardiorespiratory fitness at a single point in time and can’t show whether one is driving the other. It’s possible that having high vitamin D levels improves fitness levels, she says, but it’s also possible that someone with high fitness levels spends a lot of time exercising outdoors—and has higher vitamin D levels as a result.
“Sitting around and simply taking more vitamin D isn’t going to increase your VO2 max,” Volpe says. “You still have to exercise, and maybe if you also have high vitamin D levels your cardiorespiratory fitness may be greater.”
But higher levels aren’t always better, either. Both Volpe and Dr. Marawan caution against taking too many vitamin D supplements, which can lead to excess calcium in the blood and cause nausea, vomiting, and weakness.
Doctors don’t know yet what the ideal dose of vitamin D is for heart health or for fitness, and Dr. Marawan says more research is needed. Until then, he says, making sure your vitamin D levels are “normal or high” is your best bet for overall health. (What’s considered a normal vitamin D level is also up for debate: Some doctors say patients’ levels should be 30 nanograms per milliliter or higher, while others say levels as low as 10 or 15 can still be healthy.)
Many people get enough vitamin D through sun exposure and a healthy diet, says Volpe. But if you’re concerned about your levels, she says, ask your doctor for a test. “If your levels are fine, my advice is to maintain a healthy level of exercise and a healthy diet,” she says. “And if you’re deficient, you can work with your doctor to bring those concentrations back up with a supplement.”