The popularity of foods deficient in magnesium could provide the answer to why asthma is more common in developed rather than subsistence countries, according to medical researchers at Nottingham University.
A three-year study of more than 2,500 people in Nottinghamshire indicates that people who ate foods rich in magnesium have better lung function and a lower risk of asthma. Each person was asked to complete a lung function test, a dietary questionnaire and an examination to assess the sensitivity of their airways to irritants.
According to project leader John Britton, senior lecturer and consultant physician at Nottingham City Hospital, those in the bottom 10 per cent of the sample - who consumed foods deficient in magnesium - were three times more likely to suffer from asthmatic attacks than those in the top 10 per cent.
It has long been thought that a high salt intake increased the risk of asthma. Dr Britton found no evidence for this, but suggested that salt-rich foods were generally poor in magnesium. Magnesium relaxes the muscle that forms the airwave and helps to reduce inflammation. It is common in such foods as brown bread, cereals, green vegetables, nuts and beer. "The increase in asthma may be in part due to a deterioration in diet as people consume more and more processed foods," he said. Processed foods often have their magnesium content removed and salt added.
The Pounds 250,000 study was financed by the National Asthma Campaign and the British Lung Foundation. Dr Britton is seeking another Pounds 170,000 to re-examine the same people and assess "whether the results have held up over time".