High salt diet triggers exercise-linked asthma?

The scientists at Indiana University demonstrated, for the first time, that modifying salt intake for two weeks alters airway inflammation and the flow of oxygen into the bloodstream.

Eating too much salt is widely believed to be a significant risk factor in developing high blood pressure, itself a cause or contributing factor in the rising incidence of heart disease, the world's number one killer.

While these latest findings on asthma suggest a further reason to watch salt consumption. In the UK, one in eight children has asthma, a figure that has increased six-fold in the last 25 years, according to Asthma UK.

Recent figures from the UK's Food Standards Agency claim that every day at least 26 million people eat more than the recommended daily limit of 6g of salt. Men are eating the most with a daily average of 11.0g of salt while women consume an average of 8.1g a day.

Although this mineral is present at low levels in foods, its main source is in the diet, about 70 to 75 per cent of total intake comes from processed foods.

Condemned for contributing to the worsening health problems in the population, food makers are under orders to slash salt levels in their processed food formulations.

Targets published by Blair's government in the March 2004 White Paper on Public Health say the food industry must contribute to reducing the salt intake of the population to 6g per person per day by 2010.

The small study at Indiana University claims to offer the most complete picture to date of how dietary factors can both aggravate and alleviate the symptoms of asthma.

The randomised, double-blind, crossover study involved 24 people with asthma and exercise-induced bronchoconstriction (EIA).

Study participants on the low-salt diet consumed 1,446 milligrams of sodium per day. Participants on the high-salt diet consumed 9,873 milligrams of sodium per day, an amount the study author Timothy Mickleborough described as typical for many adults.

"Participants on the high-salt diet showed a dramatic decline in lung function after physical activity,"​ report the scientists.

Twenty minutes after exercising, the forced expiratory volume in 1 second (FEV1) - a measure of lung function - of participants on the high-salt diet had dropped by 27.4 per cent comparedto just 7.9 per cent for participants on the low-salt diet.

Mickleborough attributed this to a combination of factors caused by the high-salt diet, including high blood pressure and increased blood volume.

The scientist also found a higher percentage of airway cells, which have been implicated in the pathogenesis of asthma and EIA, in the spit of study participants on the high-salt diet, along with more proinflammatory mediators, which can cause constriction of the airways.

Earlier research from Mickleborough found that increasedconsumption of omega-3 polyunsaturated fatty acids, commonly found in fish oil, also could reduce EIA symptoms in asthmatics after just three weeks.

Full findings of the high salt study are published in the June issue of Medicine & Science in Sports & Exercise​.