EXERCISE-INDUCED ASTHMA 

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.

EIA Mechanism

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) 

Table 1

EIA Rates in Various Groups³

Group                                                         Percent

Asthmatics                                         80-90%

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.  

Table 2

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

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* # of breaths needed on a bronchodilator during the exercise tests

Next month we will explore nutritional factors that, unlike salt, reduce EIA severity.

REFERENCES

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.