New US research suggests that a combination of exercise and good levels of vitamin D could be an effective way of reducing the risk of cardiovascular disease such as heart attacks and strokes.

Carried out by researchers from Johns Hopkins University, the large-scale study looked at the survey responses and health records of 10,342 American adults with an average age of 54 for nearly a 20-year period.

Although exercise and sufficient levels of vitamin D have already been shown to reduce the risk of heart disease, the team wanted to look at what effect a combination of the two might have on heart health.

Using participants' self-reports, the team classified exercise levels as adequate, intermediate or poor and measured levels of 25-hydroxyvitamin D in the blood to asses vitamin D levels.

The team found a direct and positive relationship between exercise and vitamin D levels, with results showing that the more one exercised, the higher their vitamin D levels seemed, suggesting that exercise may boost vitamin D stores.

They also found that a combination of the two factors had a stronger positive effect on heart health than either factor alone: those who exercised the most and had the highest vitamin D levels showed around a 23 percent reduced risk of a cardiovascular disease compared to those with poor physical activity and poor levels of vitamin D.

However, those who had an adequate level of exercise, but not vitamin D, did not benefit from the same reduced risk.

Although the researchers noted that the study is an observational one and larger clinical trials would be needed to confirm results, the findings do support the idea that adequate levels of vitamin D and exercise are beneficial for good health.

The reasons for the link between vitamin D and exercise remain unclear, however Erin Michos, one of the authors, cautions that the idea that those exercising outside are getting more sun exposure may not be the full reason behind the relationship. She explains that vitamin D is produced by the skin after sun exposure, but the amount tends to level off when the body makes enough. However, the levels found in these participants didn't, suggesting other factors. People who exercise may also have other healthy habits that influence vitamin D levels such as lower body fat and a healthier diet, or may take more vitamin supplements.

Michos noted that a few minutes a day of sunlight, eating a well-balanced diet with vitamin D-rich foods such as oily fish and vitamin-D fortified cereals and milk, may be enough to provide adequate levels of vitamin D for most adults.

She added that those who have adequate levels of vitamin D don't need to take additional vitamin supplements.

The findings can be found published online in the Journal of Clinical Endocrinology & Metabolism.