Science Briefs

Breathe Easy with Vitamin C

An investigation of lung health in rural China goes one step further than previous studies and finds that even smokers can benefit from vitamin C.

Hu Guizhou, Ph.D., of Cornell University in Ithaca, New York, and Xin Zhang of the Chinese Academy of Preventive Medicine in Beijing compared the lung capacity of 3,085 people in 69 rural Chinese counties with their vitamin C intake. Vitamin C intake ranged from as much as 295 mg/day to as little as 42 mg/day. People with more vitamin C in their diet had greater lung volume—meaning they could exhale more air than those eating less of the vitamin. In fact, for each 100 mg/day increase of vitamin C, lung volume increased 22 mL. This study, completely controlled for smoking, determined the increase was the same in smokers and nonsmokers alike.

To compare geographical differences, researchers calculated the mean plasma vitamin C level for each county's population and compared it with the mean lung volume. Counties with higher plasma vitamin C levels also had greater lung capacity. Each increase of 1 mg/dL of plasma vitamin C correlated with an increase of 47 mL in exhaled air.

Vitamin C may help lung function in several ways. It is involved in the collagen formation needed to rebuild damaged lungs and in the production of prostaglandins, fatty acids that help keep airways open.

People in this study got their daily vitamin C quite differently than Americans would have—73 percent of their vitamin intake came from vegetables such as sweet potatoes and other tubers while only 2 percent came from fruits.

—American Journal of Epidemiology 1998 Nov;148(6):594-9