Exercise as it relates to Disease/The effect of weight loss strategies on obese asthmatics

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This is an analysis of the article "Immediate and long term effects of weight reduction in obese people with asthma: randomised controlled study", by Stenius-Aarniala B. et al (2000).[1]

Background[edit]

Both asthma and obesity are on the rise in developed countries, and while research has been done into both the effects of exercise on asthma and the relationship between asthma and obesity, very little has been done into lifestyle treatments for obese asthmatics.

The research[edit]

Participants[edit]

The study [1] was based in a private outpatients centre in Helsinki, Finland, with the aim to identify the benefits of weight loss (achieved through dieting) on the symptoms of asthma in obese asthmatics. The study consisted of 38 participants with BMIs of 30-42 (aged 18–60) who had been previously diagnosed with asthma. Various other conditions that could affect a participant’s reaction to the dieting plan were also accounted for and excluded (e.g. pregnancy, allergies, various glandular diseases etc.). Participants underwent a clinical examination to ensure the severity of their asthma (and medication) was acceptable.

While the researchers secured a range of participants and screened for medical conditions that may interfere with the results, they only used a relatively small sample size, and consequently the results cannot be extrapolated to the wider population. They can, however, be used to direct further research and provide a basis for discussion.

Procedure[edit]

After 2 weeks of baseline measures of lung function, the subjects were randomly split into two groups, each of 19 people: a control group and a treatment group. The treatment group underwent a 14 week weight loss regime, consisting of a reduced intake diet.

All participants took daily peak expiratory flow (PEF) measures. Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were also measured in a clinical setting at less regular intervals, as was use of rescue medication (inhaler puffs), a visual analogue scale (VAS) of symptom severity (cough and dyspnoea) and various blood/urine concentrations (cortisol, cholesterol, triglycerides and salts). The St George’s respiratory questionnaire (SGRQ) was also used. The study lasted for 1 year, with post-treatment check-ups at 6 months and 1 year, and regular group meetings for both groups.

The two weeks for baseline measures allowed the researchers to see the day-to-day variance and account for them later in the study. It would have also ensured that the participants were adequately trained and confident in measuring their own PEF. Use of the SGRQ and visual analogue scale provided already-proven references with which the researchers could compare their findings.

The results[edit]

The results were presented in 5 categories: weight reduction, lung function, symptoms, health status (as measured by the SGRQ) and laboratory values (blood/urine concentrations).

Weight reduction[edit]

The treatment group lost a mean of 14.5% pre-treatment weight by the end of the 14 week diet, which reduced to 11.3% after 1 year. By contrast, the control group had negligible weight change after 14 weeks and an increase of 2.2% after 1 year.

These results are in-line with expectations, as the treatment has resulted in significant weight loss, while the control group has maintained a consistent weight. This means any resulting changes to lung function or asthma symptoms can be (at least partially) attributed to weight loss.

Lung function[edit]

To normalise the results for lung function, all values were analysed as a percentage of predicted value. The PEF measures of the treatment group did not improve significantly; however, both the FEV1 and the FVC in the treatment group increased significantly relative to the control group, at both 14 weeks and 1 year.

Symptoms[edit]

The VAS measures of symptom severity decreased slightly in the treatment group; however, this change was not statistically significant. There was also no significant reduction in use of rescue medication.

Health status[edit]

The SGRQ results are indicative of an individual’s quality of life,[2] and scores for the treatment group improved significantly after 1 year.

Laboratory results[edit]

Blood composition did not change significantly during the study; however, urine sodium and magnesium concentrations decreased in the treatment group. The table below summaries the results of the treatment group.

Parameter Significant (positive) change
Weight yes
PEF no
FVC yes
FEV1 yes
VAS no
Use of medication no
Health status yes
Blood composition no
Urine salt concentration yes

Conclusions[edit]

The weight loss in the treatment group correlated with an increase in both FVC and FEV1, which are measures of “useable” lung volume, and are typical clinical measures of lung function. This result can be explained by the mechanical forces that excess abdominal fat imposes on the lungs. By reducing their abdominal fat, the treatment group reduced the restrictive force exerted on their lungs, causing airways to remain open for longer during a forced expiration, resulting in an increased “useable” lung volume, and consequently higher FVC and FEV1 measures. The improvements in health status could be similarly explained, although the lack of change in the VAS and use of medication would indicate that there was no change in the hyper-responsiveness of airways, which is the cause of acute asthma attacks.

The researchers also concluded that the changes in urine salt concentrations (sodium and magnesium) did not affect the symptoms of asthma, although there was literature on the possible (positive) effects of decreasing sodium and (negative) effects of decreasing magnesium.

Ultimately, these results led the researchers to conclude that a weight loss diet regime is a suitable clinical treatment for asthma in an obese population, as benefits can be achieved at a reasonable cost. This conclusion concurs with the study performed by Hakala et al [3]

Future implications[edit]

This study identified some benefits to weight loss for obese asthmatics, specifically lung function/capacity, and an improved quality of life.

Additional research would be needed to explore the effectiveness of other methods of weight loss, specifically exercise.

Further reading[edit]

  • Farah CS. and Salome CM. (2012) 'Asthma and obesity: A known association but unknown mechanism' Respirology, 17(3), 412-421.
  • Lucas SR. and Platts-Mills TAE. (2006) 'Paediatric asthma and obesity' Paediatric Respiratory Reviews, 7(4), 233-238.

References[edit]

  1. a b Stenius-Aarniala, B. et al. (2000) 'Immediate and long term effects of weight reduction in obese people with asthma: randomised controlled study', BMJ : British Medical Journal, 320(7238), 827–832.
  2. American Thoracic Society (2015) 'St. George's Respiratory Questionnaire (SGRQ)', http://www.thoracic.org/members/assemblies/assemblies/srn/questionaires/sgrq.php
  3. Hakala K et al (2000) 'Effects of weight loss on peak flow variability, airways obstruction, and lung volumes in obese patients with asthma' Chest journal, 118(5), 1315-1321.