Dr Paul Clayton 2004
Higher levels of the antioxidants beta-carotene and Vitamin C, along with the antioxidant trace mineral selenium, have been linked with a lower risk of asthma in a large study of 6000 American children under the age of 17, published in February 2004. The antioxidants showed even stronger protection against asthma in children exposed to passive smoke, said the researchers from Cornell University, New York.
Vitamin E had little or no association with asthma. However, an increased beta-carotene intake was associated with a 10 to 20 per cent reduction in asthma in those not exposed to smoke, and a huge 40 per cent reduction in young persons who had passive smoke exposure. The pattern for Vitamin C was similar, as were the protective effects of selenium.
VERDICT: This was a poor study, and a waste of research funds, carried out with little apparent understanding of the biochemistry of asthma.
In asthma the basic condition does involve a degree of oxidative stress, but the main element in the disease is chronic inflammation of the airways. A diet rich in fruits and vegetables has long been known to reduce the risk of asthma, but the key anti-inflammatory ingredients in plant foods are not the antioxidant vitamins! This was recognised in an earlier and altogether more sophisticated study.
Cassano P et al, American Journal of Respiratory and Critical Care Medicine 169:393-398, 2004