In a review of 40 studies researchers have found that a diet low in vitamins A and C is associated with an increased risk of developing asthma.

Lead researcher Dr. Jo Leonardi-Bee says “the study findings indicate that low levels of vitamin C intake, and to a lesser extent, vitamin A are consistently associated with asthma risk to a degree that, if causal, would be sufficient to be clinically relevant.”

The findings of this research contradict the results of a large-scale study published last year, which found no link between levels of antioxidants in the diet and asthma, but the researchers say their study is more robust.

A total of 13 studies related to children while the rest were related to adults or were unspecified. They found no link between vitamin E and asthma, but said the associations for A and C were significant, and on average, men with asthma were lacking 26% of their daily requirements of vitamin A, while women with asthma were lacking 30%.

The UK has one of the highest prevalence rates for asthma in the world. The 2001 Asthma Audit by the National Asthma Campaign estimated that 5.1 million people, 1 in 13 adults and 1 in 8 children, are currently being treated for asthma.

Approximately 20 million Americans have asthma, and the prevalence of asthma is increasing.

Dr. Leonardi-Bee says it is now important that larger-scale studies are carried out in order to clarify the link and to see if there was a direct cause between vitamin intake and asthma.

Some dietary sources of vitamin C are kiwi fruit, oranges, green peppers, papaya, grapefruit, cantaloupe, strawberries, mango, watermelon, cabbage, broccoli, tomatoes, Brussels sprouts, and cauliflower. Leafy greens such as spinach, red and green peppers, canned and fresh tomatoes, potatoes, winter squash, raspberries, blueberries, cranberries, and pineapple are also good sources of vitamin C.
References:
1. S. Allen, J.R. Britton, J.A. Leonardi-Bee. Association between antioxidant vitamins and asthma outcome measures: systematic review and meta-analysis. Thorax, doi: 10.1136/thx.2008.101469.
2. Agricultural Research Service Nutrient Database for Standard Reference.
3. National Institutes of Health.
4. Image by  roseannepage.