"Although there is a definite relationship between lung function and vitamin D, it is unclear if increases in vitamin D through supplements or dietary intake will actually improve lung function in patients with chronic respiratory diseases," Dr Peter Black, who led the study, said.

Dr Black, an associate professor in the university's Department of Medicine, and his team analysed information from the US National Health and Nutrition Examination Survey, which collected data on 14,091 people from 1988 to 1994.

Their new analysis found those who had higher levels of vitamin D were able to inhale and exhale more air.

That link was seen in blacks and non-Hispanic whites and was stronger in people older than 60 and smokers. Non-Hispanic blacks and Mexican-Americans showed lower levels of the vitamin compared to whites.

The study, funded by the Health Research Council of New Zealand, also found levels of the nutrient were higher among men and lessened as people aged or gained weight.

Dr Rosalind Wright, a professor at Harvard Medical School's Department of Society, Human Development, and Health, said the vitamin could be an easy way to boost lung function.

"Vitamin D would be a relatively simple, low-cost intervention that would likely have high compliance to prevent or slow loss of lung function in susceptible subgroups," Dr Wright said.

She said more studies were needed to see who would benefit most.

Other recent studies have suggested Vitamin D may help strengthen bones as well as prevent some cancers and multiple sclerosis.