How Dietary Deficiencies Effect Asthma

Summary
The marked increase in prevalence of asthma in Western countries has made it a major health concern. The reason for this increase is attributed to the reduction in consumption of antioxidants in diet, vitamin D deficiency and alteration in the balance of polyunsaturated fatty acids (PUFA). This study highlights and reviews previous research related to each of these factors. It also reviews the associations between asthma and diet, and between childhood asthma and the reduction in nutrients consumed by the mother during pregnancy.

Introduction
Asthma is a chronic disorder, which has an increasing prevalence especially in North America. The prevalence in North America is 11.2 percent, representing 35.5 million people in a population of 316.9 million. Over the last few years, changing dietary patterns have contributed significantly to the increase in the incidence of asthma. “Given the high prevalence of asthma and its affect on individuals and society there is a need to identify interventions that can be used to complement conventional asthma therapy and more importantly, interventions to reduce the likelihood of children developing asthma,” state the study researchers. This study highlights the rationale for investigating the link between diet and asthma and complementing the conventional asthma treatment with dietary nutrients.

Methodology
•    A total of 117 search terms related to asthma and diet such as “symptoms of asthma,” clinical outcomes and specific nutrients were used to search the Cochrane Library, MEDLINE and EMBASE for relevant articles.
•    Out of 1,457 identified articles, 329 were directly relevant and these were reviewed.
•    These articles were classified into systematic reviews, intervention, and observational studies. “In the absence of systematic reviews and interventional study data, illustrative examples of the best available observational studies are presented.”

Results
•    Although data suggests an association between diet and asthma, the nature of the associations and the effect of diet in the different stages of life are unclear.
•    Further work is required to assess the dietary benefit in asthma, especially in children and, similarly, in genetically susceptible individuals with asthma.
•    From the current data, it appears that supplementation of vitamin C, vitamin E, selenium, and n-3 PUFA-rich fish oil has minimal if any clinical benefit in established asthma.
•    A combination of fish oil with some longer chain n-6 PUFAs may be more effective.

Shortcomings/Next steps
The assumption that vitamin E plays a role in preventing childhood asthma is weak. Several studies have doubted this assumption. Specific factors entailing further investigation should assess whether PUFA could be supplemented in the case of pregnant women, to prevent childhood asthma. ”Further work, particularly in children, is required to establish if dietary intervention with individual nutrients, nutrient combinations, or food has a role in complementing conventional asthma treatment.”

Conclusion
From the interpretation of previous studies it is quite clear that, currently, the addition of most nutrients such as vitamin C, vitamin E, selenium and PUFA-rich fish oil to diets has very less clinical benefit. Further research work, needs to be done to establish a relationship between dietary intervention and its effect on asthma. “Until the results of ongoing and planned trials are available, the practical consequences of research linking diet with asthma are minimal, and based on the available evidence, people with asthma, pregnant women, parents, and children should not be advised to change or supplement their diet to treat or reduce the risk of developing asthma.”

For More Information:
Diet and Asthma: Nutrition Implications from Prevention to Treatment
Publication Journal: Journal of the American Dietetic Association, February 2011
By Keith Allan; Graham Devereux, MD; Institute of Health Sciences and Royal Aberdeen Children’s Hospital Department of Child Health, University of Aberdeen, Scotland

*FYI Living Lab Reports Are Summaries of the Original Research.