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.
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.
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.
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