Telling children to eat up their greens – and giving them a helping of liver – may be the best way to prevent them from developing asthma.
Researchers who examined the influence of diet on asthma found that people who did not get enough vitamin A or C from their food had a higher risk of becoming asthmatic. Vitamin A is found in dark green and yellow vegetables such as broccoli, spinach and turnip greens, carrots, squash and sweet potatoes. It is also found in liver, milk, butter, cheese and eggs. Vitamin C is found in many of the same vegetables and in fruits including oranges, lemons, pineapple and strawberries.
Low levels of vitamin C in the blood were associated with a 12 per cent rise in incidence of the disease. Analysis also showed that those with asthma had an average daily intake of vitamin A which was between a quarter and a third of the recommended level.
Those with severe asthma had the lowest levels of vitamin A. No association was found with vitamin E.
The findings are from one of the largest reviews of research into the link. Scientists from the University of Nottingham found 40 relevant studies conducted around the world between 1980 and 2007.
Jo Leonardi-Bee, from the university's Department of Public Health, who led the study published in the journal Thorax, said: "It does appear that there is a link between diet and respiratory disease. It is unclear what the link is but it is probably to do with the anti-inflammatory properties of vitamins."
Asthma, which affects an estimated five million people in Britain, is characterised by oversensitive airways in the lungs which react to irritants in the air such as pollution and tobacco smoke.