Abstract
The purpose of the study was to determine whether reducing dietary salt intake potentially would improve pulmonary function and airway responsiveness in individuals with asthma; i.e. whether the severity of asthma could be reduced by reducing dietary salt intake (Mickleborough and Gotshall, 2004). For this the authors have relied on data from two types of studies: existing studies that support a role for dietary salt reduction for reducing severity of asthma in individuals with asthma; and existing studies that have altered dietary salt and evaluated exercise induced bronchoconstriction in nonatopic individuals.
The authors admit that the first type of studies suffered from a variety of experimental and population limitations, but they found the data from the latter type of studies more clinically convincing. The first part of the literature review includes very early studies such as that of Stoesser and Cook (1938) and Burney and colleagues (1986, 1989). These studies showed positive correlation of salt intake with airway responsiveness. The study by Schwartz and Weiss (1990) emphasized that dietary electrolytes may contribute to airway responsiveness and does nothing to prove the correlation between dietary salt and severity of asthma.
The study by Demissie et al. (1996), vaguely hints on a relationship between airway responsiveness and salt intake. The interventional studies cited by the authors add support to the correlation between salt consumption and asthma: – Javaid and colleagues (1988), Burney and coworkers (1989), Carey et al. (1993) and Medici et al. (1993), Tribe and colleagues (1994) and Lieberman and Heimer (1992).
The second part of the literature review considers studies based on exercise induced bronchoconstriction. Studies by Mickleborough and colleagues (2000, 2001a, 2001b) and the studies by Gotshall and coworkers (2000, 2003) support the finding that the low-salt diet improved and the high-salt diet worsened post exercise pulmonary function values in EIB subjects. Mickleborough and colleagues (2001c) found that altering dietary salt consumption also exacerbated HIAO (Hyperpnea-induced airway obstruction) in guinea pigs. These set of studies that are based on exercise induced bronchoconstriction are more clinically conclusive and provide evidence for positive correlation between salt intake and severity of asthma.
Article balance
The writers have addressed both sides of the issue with a strong bias towards favoring a positive correlation between salt intake and asthma. Evidence for this bias can be seen in the choice of articles cited by the writers. Almost all the articles cited in the literature review, amidst limitations, support the finding that reduced dietary salt intake can reduce the severity of asthma. The authors have included articles that even mildly favor reduced dietary salt intake for treatment of asthma.
For example, the study by Schwartz and Weiss (1990) only indirectly emphasizes that dietary electrolytes may contribute to airway responsiveness and does nothing to prove the correlation between dietary salt and severity of asthma. The study by Pistelli et al. (1993) does not provide any solid data to suggest any link between salt consumption and asthma severity. The study by Demissie et al. (1996) just hints on a relationship between airway responsiveness and salt intake.
Many other articles that strongly favor this argument have been elaborated in detail: Carey et al. (1993); Medici et al. (1993); Tribe and colleagues (1994) and Lieberman and Heimer (1992); Mickleborough and colleagues (2000, 2001a, 2001b) and the studies by Gotshall and coworkers (2000, 2003). On the other hand studies that deny the link between dietary salt intake and asthma are just mentioned and not elaborated: Britton et al., 1994; Devereux et al., 1995; Sparrow et al., 1991; Zoia et al., 1995. None of these studies have been expanded in detail. This shows that the authors have a strong bias towards the hypothesis that reduced dietary salt intake can reduce the severity of asthma.
Article Quality
The article is of excellent quality – well researched, simple language used and hypothesis is clearly stated. The paper is written in an easy and fluid style with meticulous formatting. The logical presentation is excellent and the authors take care to explain what is meant by asthma therapy, airway responsiveness, hyperpnea, exercise induced bronchoconstrction, how and why EIB has been considered in this context. Only one graph and one table have been used.
More graphs and tables could have been used to graphically illustrate the findings by various studies. The relation between salt intake and blood pressure has been included in the paper which is irrelevant to the central hypothesis. It is significant to note that wherever possible, the writers have provided the limitations to the various studies as well and have provided a broad critique about the articles as well. There is a contradiction in the two sets of studies, used by the writers.
While the first set of studies (Burney and coworkers (1989); Carey et al (1993) and Pistelli et al (1993)) indicates that women react different to a low salt diet than men, the studies based on EIB do not provide any support for that argument. Burney and colleagues (1986) found that there was no link between mortality due to asthma and table salt purchases in the case of women. More research needs to be done regarding this aspect. I agree fully with the article and it supported my opinion that salt is generally bad for health.
Bibliography
Britton J; Pavord I; Richards K; Knox A; Wisniewski A; Weiss S and Tattersfield A (1994). Dietary sodium intake and the risk of airway hyperreactivity in a random adult population. Thorax 1994, Vol. 49, p. 875–880.
Burney PG; Chinn S; Britton JR; Tattersfield AE; and Papacosta AO (1989). What symptoms predict the bronchial response to histamine? Evaluation in a community survey of the bronchial symptoms questionnaire (1984) of the International Union against Tuberculosis and Lung Disease. Int J Epidemiol 1989, Vol. 18, p. 165–173.
Burney PGJ; Britton JR; Chinn S; Tattersfield AE; Platt HS; Papcosta AO; and Kelson MC (1986). Response to inhaled histamine and 24 hour sodium excretion. Br Med J, Vol. 292, p. 1483–1486.
Carey OJ; Locke C and Cookson JB (1993). Effect of alterations of dietary sodium on the severity of asthma in men. Thorax, Vol. 48, p. 714–718.
Demissie K; Ernst P; Gray Donald K and Joseph L. (1996). Usual dietary salt intake and asthma in children: a case-control study. Thorax, Vol. 51, p. 59–63.
Devereux G; Beach JR; Bromly C; Avery AJ; Ayatollahi SM; Williams SM; Stenton SC; Bourke SJ; Hendrick DJ (1995). Effect of dietary sodium on airways responsiveness and its importance in the epidemiology of asthma: an evaluation in three areas of northern England. Thorax, Vol. 50, p. 941–947.
Gotshall RW; Fedorczak LJ; Rasmussen JJ (2003). One week versus two weeks of a low salt diet and severity of exercise-induced bronchoconstriction [abstract]. Med Sci Sports Exerc, Vol. 35, p. S10.
Gotshall RW; Mickleborough TD; Cordain L (2000). Dietary salt restriction improves pulmonary function in exercise-induced asthma. Med Sci Sports Exerc, Vol. 32, p. 1815–1819.
Javaid A; Cushley MJ and Bone MF (1988). Effect of dietary salt on bronchial reactivity to histamine in asthma. BMJ, p. 297:454.
Lieberman D and Heimer D (1992). Effect of dietary sodium on the severity of bronchial asthma. Thorax, Vol. 47, p. 360–362.
Medici TC; Schmid AZ; Hacki M; Vetter W (1993). Are asthmatics saltsensitive? A preliminary controlled study. Chest, Vol. 104, p. 1138–1143.
Mickleborough TD, Gotshall RW, Rhodes J, Tucker A, Cordain L. Elevating dietary salt exacerbates hyperpnea-induced airway obstruction in guinea pigs. J Appl Physiol 2001c;91:1061–1066.
Mickleborough TD; Cordain L; Gotshall RW; and Tucker A (2000). A low sodium diet improves indices of pulmonary function in exerciseinduced asthma. J Exerc Physiol, Vol. 3, p. 46–54.
Mickleborough TD; Gotshall RW; Cordain L; and Lindley M (2001a). Dietary salt alters pulmonary function during exercise in exercise-induced asthmatics. J Sports Sci, Vol. 19, p. 865–873.
Mickleborough TD; Gotshall RW; Kluka EM; Miller CW and Cordain L (2001b). Dietary chloride as a possible determinant of the severity of exercise-induced asthma. Eur J Appl Physiol, Vol. 85, p. 450–456.
Mickleborough, D. Timothy and Gotshall, W. Robert (2004). The Journal of Alternative and Complementary Medicine. Volume 10, Number 4, p. 633–642
Pistelli R; Forastiere F; Corbo GM; Dell’Orco V; Brancato G; Agabiti N; Pizzabiocca A; and Perucci CA (1993). Respiratory symptoms and bronchial responsiveness are related to dietary salt intake and urinary potassium excretion in male children. Eur Respir J, Vol. 6, p. 517–522.
Schwartz J and Weiss ST (1990). Dietary factors and their relation to respiratory symptoms. The Second National Health and Nutrition Examination Survey. Am J Epidemiol, Vol. 132, p. 67–76.
Sparrow D; O’Connor GT; Rosner B and Weiss ST (1991). Methacholine airway responsiveness and 24-hour urine excretion of sodium and potassium. The Normative Aging Study. Am Rev Respir Dis, Vol. 144, p. 722–725.
Stoesser A and Cook M.(1938). Possible relation between electrolyte balance and bronchial asthma. Am J Dis Child, Vol. 56, p. 943–944.
Tribe RM; Barton JR; Poston L; and Burney PG (1994). Dietary sodium intake, airway responsiveness, and cellular sodium transport. Am J Respir Crit Care Med, Vol. 149, p. 1426–1433.