Part 1 - Salt
Government statistics show that over 24 million Americans suffer from asthma. This is approximately 12-15% of the adult population over age 18.1 Asthma attacks can be serious and in 2005 caused of death of 3884 Americans2. Exercise-induced asthma (EIA) affects 80-90% of asthma patients3. A recent survey revealed that only 21% of National Collegiate Athletic Association trainers who responded said that their athletic departments had specific written protocols for exercise-induced asthma and/or bronchospasms when they occurred during practices or games.4
EIA Defined & Diagnosed
Forced expiratory volume (FEV1) is the amount of air that can be forcefully exhaled in one second after taking a deep breath. A post-exercise FEV1 reduction greater than 7% indicates abnormal pulmonary function. Exercise-induced asthma is defined by a 10% or greater reduction in FEV1 following bronchoprovocation5. EIA is usually diagnosed when exercise causes coughing, wheezing, shortness of breath, chest tightness and premature fatigue.
At rest, we breathe through our noses. Our sinuses warm and filter the air. When we begin to exercise, we breathe through our mouths due to the increased amount of air required. Individuals who suffer from asthma, allergic rhinitis, respiratory disease or overly sensitive tissues are vulnerable to bronchoconstriction when large amounts of air suddenly reach the lungs. (See table 1)
EIA Rates in Various Groups3
Allergic rhinitis 35-45%
No respiratory disease 3-10%
Total Population 12-15%
Other triggers for exercise-induced asthma include the duration and intensity of exercise itself, the level of fitness, recent upper respiratory infection and triggers in the air (see table 2) we breathe.
EIA Air Triggers
Cold Air Dry Air
Smoky Air Dusty Air
Polluted Air Thin Air
Air with High Pollen Levels
The Salt Connection
In a review on nutrition and asthma6, it was concluded that (in EIA patients) salt increases airway sensitivity and causes a greater bronchoconstrictor response to exercise. Salt impedes arterial oxygen saturation in EIA patients by increasing capillary permeability. Salt promotes leukotriene & interleukin production leading to the formation of mucus & edema. When mucus & edema are present, the airway diameter is reduced. Suddenly the EIA patient has two additional problems in addition to the original trigger—a lack of oxygen in the blood, and a reduction in the amount of oxygen they can inhale. This double deficit further strains the body, resulting is an asthma-like symptom complex. When dietary salt is reduced, the above reactions are reversed and the overall reaction to exercise is tempered. In a recent double blind study7, 24 subjects with EIA preformed an exercise challenge test to establish a baseline, and then a test each 14 days after following either a low (~1450 mg sodium per day), moderate (~3500 mg/Na/d) or high (~9900 mg/Na/d) sodium diet. The results were as follows:
Two Weeks of Low, Medium & High Salt Diets
& Their Effect on Airway Reactivity in EIA Patients
Dietary Salt Low Medium High
FEV1 -7.9% -18.3% -27.4%
*Puffs 12 18 26
* # of breaths needed on a bronchodilator during the exercise tests
Next month we will explore nutritional factors that, unlike salt, reduce EIA severity.
1. U.S. Department of Health and Human Services, Center for Disease Control and Prevention, National Center for Health Statistics.
Vital and Health Statistics Series 10, #235, 12-2007. p. 20
2. Kung, H.C., Hoyert, D.L., Xu, J., Murphy, S.L. National Vital Statistics Report. 2008 56(10)
3. Hough, D.O, Deck, L. Exercise-Induced Asthma and Anaphylaxis. Sports Med. 1994;18(3) p. 162-172.
4. Parsons, J.P., Pestritto, V., Phillips, G., et al. Management of Exercise- Induced Bronchospasm in NCAA Athletic Programs. Med. Sci. Sports Exerc. 2008;41(4) p.737-741.
5. Rundell, J.W., Wilber, R.L., Szmedra, L., et al. Exercise-Induced Asthma Screening of Elite Athletetes; Field Versus Laboratory Exercise Challenge.
Med. Sci. Sports Exerc. 2000;32(2) p.309-316.
6. Mickleborough, T. D. A Nutritional Approach to Managing Exercise- Induced Asthma. Excer. Sport Sci. Rev. 2008; 36(3) p.135-144.
7. Mickleborough, T.D., Lindley, M.R., Ray, S., et al. Dietary Salt, Airway Inflammation, and Diffusion Capacity in Exercise-Induced Asthma. Med. Sci. Sports Exerc. 2005;37(6) p.904-919.