In the study, published in the European Journal of Preventive Cardiology, participants with the most vitamin D in their blood had VO2 maxes that were almost three times as high as those with the lowest levels.
The results are particularly interesting because there’s almost no research linking nutrition to cardiorespiratory fitness, says Robert DiSilvestro, Ph.D., a nutritional biochemist and sports nutrition expert at the Ohio State University in Columbus, who was not affiliated with the study.
Vitamin D helps your body absorb calcium and improves blood flow, he explains. Better blood flow means more oxygen gets transported to your muscles and organs. The more O2 that reaches your muscles, the more it can be used to convert glucose into energy, helping you move more efficiently during your workout and at higher intensities. This result in turn could up your VO2 max.
Interval training is still the best way to improve your VO2 max, but serum vitamin D levels between 30 and 40 ng/mL seem to the most beneficial for athletic performance. Get your baseline levels tested by your doctor, who can give you personalized supplement recommendations.