April 17 -- THURSDAY, April 16 (HealthDay News) -- People who don't get enough of the antioxidant vitamins A and C in their diet may be at increased risk for asthma, British researchers say.
The pooled results of 40 studies conducted between 1980 and 2007 showed that people with asthma had a significantly lower dietary intake of vitamin A than those without the disease. The average intake among those with asthma was 182 micrograms a day, which is between a quarter and a third of recommended daily intake.
The review authors also found that people with severe asthma had a significantly lower intake of vitamin C (about half the recommended daily intake) than those with mild asthma. In addition, low circulating levels of vitamin C in the blood and lower dietary intake of foods containing vitamin C were associated with a 12 percent increased risk of asthma.
There was no association between vitamin E intake and asthma risk, but blood levels of vitamin E were much lower among people with severe asthma than in those with mild asthma. Those with severe asthma had an average vitamin E intake of 2 milligrams/day, which is 20 percent lower than the daily recommended amount, the review authors said.
These findings don't prove cause and effect, but they do challenge a study published last year that found no association between antioxidants and asthma risk, said Dr. Jo Leonardi-Bee, of the division of epidemiology and public health at the University of Nottingham in the United Kingdom, and colleagues.
"Overall, our findings from [the current] systematic review and meta-analysis 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," they concluded.
Their findings for an association between dietary antioxidants and wheezing were less consistent. The report was published in the current issue of Thorax.
The U.S. National Heart, Lung, and Blood Institute has more about asthma.
SOURCE: BMJ Specialist Journals, news release, April 15, 2009