One of the most frequent triggers of asthma is strenuous exercise. A new study1 done at Indiana University is the first to show that reducing salt intake for just two weeks can reduce airway inflammation, and improve the flow of oxygen into the bloodstream. The study was done on 24 people with asthma who had experienced exercise-induced asthma. The subjects were put on either a low-salt diet (1,446 mg of sodium/day) or a high-salt diet (9,873 mg of sodium/day). This high-salt amount is not unusual for many athletes who have high calorie requirements and use sports drinks like Gatorade.
After two weeks, those following the high-salt diet showed a dramatic decline in lung function after physical activity. Their lung function dropped by 27.4% over the two weeks, compared with only a 7.9% decline for those on the low-salt diet. A decline of more than 10% in post-exercise forced expiratory volume is considered abnormal. High-salt diets have many adverse physiological effects that are likely to impair athletic performance in the short run such as increased blood volume and elevated blood pressure, which increases the work load on the heart. Higher blood pressure and increased blood volume can also lead to pulmonary swelling, which results in airway obstruction.
The study volunteers on the high-salt diet also had higher levels of airway cells in their sputum. An increased number of airway epithelial cells is associated with development of asthma. The people on the high-salt diet also had more pro-inflammatory mediators, which can cause airway constriction. Sadly, many athletes are encouraged to consume sports drinks loaded with salt and eat more salt-rich foods in a misguided attempt to avoid hyponatremia.
The Bottom Line: It is increasingly clear that advice to athletes to consume salt-rich electrolyte drinks and/or eat more salt-rich foods may be detrimental to their athletic performance. A high-salt intake also promotes hypertension.
By James Kenney, PhD, RD, FACN
1. Medicine & Science in Sports & Exercise. 37(6):904-914, June 2005.
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.