New research has suggested that adding extra vitamin D in your diet could help boost your fitness levels.
The study published in the European Journal of Preventative Cardiology surveyed 2,000 people between 20 and 49 years old.
They had blood tests taken to ascertain their vitamin D levels before doing some intensive cardio on the treadmill.
The test subjects were then split up into groups based on their vitamin D levels, and it was found that those with higher levels had the highest level of cardiorespiratory fitness.
"Our study shows that higher levels of vitamin D are associated with better exercise capacity," assistant professor of internal medicine at Virginia Commonwealth University Dr Amr Marawan said.
"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."