Carotenoids are oil-soluble plant pigments responsible for the bright colors of fruits and vegetables. Some carotenoids can be converted by the body into vitamin A. The best-known carotenoid is beta-carotene, which has the greatest vitamin A activity. Other carotenoids include alpha-carotene, lycopene, lutein, astaxanthin, beta-cryptoxanthin, and zeaxanthin.
A randomized, placebo-controlled study published in the American Journal of Clinical Nutrition (2012;96[3]:534–543) examined the effects of dietary antioxidant intake in 137 adults with asthma. For two weeks, participants consumed either a high-antioxidant diet (five servings of vegetables and two servings of fruit daily) or a low-antioxidant diet (fewer than two servings of vegetables and one fruit daily). Participants in the low-antioxidant group also received either a tomato extract providing 45 mg of lycopene or a placebo.
After two weeks, those consuming the high-antioxidant diet showed significant improvements in lung function, including forced expiratory volume and predicted forced vital capacity. In contrast, participants on the low-antioxidant diet experienced an increase in C-reactive protein, indicating higher inflammation. Lycopene supplementation did not improve lung function or reduce inflammation in those eating a low-antioxidant diet.
The key finding: a diet naturally rich in carotenoid-containing fruits and vegetables improved respiratory function in people with asthma, whereas isolated carotenoid supplementation did not replicate these benefits.
