Exercise-induced bronchoconstriction – a narrowing of the airways in response to exercise – occurs in as much as 10 percent of the general population and up to 50 percent in some fields of competitive athletics. Findings from a meta-analysis suggest that vitamin C might reduce the incidence of exercise-induced bronchoconstriction.

Previous research demonstrated that vitamin C can triple respiratory tissue levels within an hour or two of a single oral dose of 1 or 2 grams. This local increase in vitamin C concentration appears to protect against acute increases in airway oxidative stress. In addition, vitamin C inhibits the production of prostaglandins and leukotrienes, biological compounds that participate in the pathogenesis of exercise-induced bronchoconstriction.

In addition, vitamin C halved the incidence of the common cold among people experiencing heavy short-term physical stress – an indication that vitamin C might also have other effects on people experiencing heavy physical exertion.

The authors of the current conducted analyses of nine studies that investigated varied aspects of the effects of vitamin C on exercise-induced bronchoconstriction. Three placebo-controlled studies analyzed the relative exercise-induced decline in forced expiratory volume, or FEV1, (a measure of respiratory capacity) with or without a vitamin C. They found that doses ranging between 0.5 and 2 grams of vitamin C reduced FEV1 decline by half. Similarly, five studies investigated the effects of vitamin C supplementation on respiratory symptoms after short-term heavy physical work and found that incidence was halved. One study investigated the duration of respiratory symptoms in young male swimmers and also found that incidence was halved.

The authors noted that a variety of factors might influence whether and to what degree vitamin C affects respiratory function during exercise, including the type of activity and the conditions under which it is performed, among others.

• Link to full study.