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Health News Archive 495 - Asthma
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Fish and Whole Grains Linked to Asthma Protection

An increased consumption of whole grains and fish reduces the risk of developing asthma by about 50 percent, suggests a new study from The Netherlands.

It has been suggested that the skyrocketing rates of asthma in western societies may be related to two nutritional changes:

• Decreased intakes of fruits and vegetables
• Replacing saturated fat in the food supply with omega-6 fatty acids (margarine, vegetable, soybean, corn oil)

Both of these changes started in the 1950’s and are thought to lead to increased airway inflammation.

The International Study on Allergy and Asthma in Childhood 2 (ISAAC-2) looked at dietary intakes for a range of foods, including fish, fruits, vegetables, dairy and whole grain products, for 598 Dutch children aged between 8 and 13.

“Our findings suggest that a high intake of whole grain products and fish may have a protective effect against asthma in children,” wrote lead author Dr. Cora Tabak in the current issue of the journal Thorax.

According to the American Lung Association, almost 20,000,000 Americans suffer from asthma. The condition is reported to be responsible for over 14,000,000 lost school days in children, while the annual economic cost of asthma is said to be over $16.1 billion.  “The rise in the prevalence of asthma in western societies may be related to changed dietary habits,” said Dr. Tabak.

The researchers, from the Dutch National Institute of Public Health and the Environment, Utrecht University, University Medical Center Groningen, used semi-quantitative food frequency questionnaires completed by the children's parents to assess dietary intakes for a range of food items. Data on asthma and wheezing were also assessed using questionnaires, and also from medical tests.

Tabak and co-workers report that intake of fruits, vegetables, and dairy products were not associated with asthma, a result that is at odds with other studies that supported a link between antioxidant intake, particularly vitamins C and E, to the incidence of asthma.

However, both whole grains and fish were related to asthma incidence, said the researchers. In children with a low intake of both foods, the prevalence of wheezing was almost 20 percent, but this was significantly less in children with a high intake of both foods demonstrating a 4.2 percent wheezing prevalence. Low intake of fish and whole grains was also linked to a higher prevalence of current asthma (16.7 percent) compared to high intake of both foods (2.8 percent).

After adjusting the results for possible confounding factors, such as total energy intake, Tabak reports that high intakes of whole grains and fish were associated with a 54 and 66 percent reduction in the probability of being asthmatic, respectively. The probability of having asthma with bronchial hyperresponsiveness (BHR), defined as having an increased sensitivity to factors that cause narrowing of the airways, was reduced by 72 and 88 per cent when children had a high-intake of whole grains and fish, respectively.

Additional research is needed to further investigate the potential link between fish and whole grain intake, as well as the reason why no relationship between fruit and vegetable intake was observed, in contradiction to other studies.

A study published earlier this year in the journal Chest (Vol. 129, No. 1, pp. 39-49) also reported a link between fish intake and protection against exercise-induced bronchoconstriction (EIB) in asthma sufferers. EIB is a temporary narrowing of the airways that can be triggered by vigorous exercise measured changes in a variety of markers that together appeared to contribute.

The researchers also reported a decrease in the levels of the inflammatory marker leukotriene LTB4, proinflammatory cytokines, and a partial replacement of arachidonic acid (AA) in inflammatory cell membranes.

The researchers believe the health effects of fish consumption in relation to asthma may lie in their content of the omega-3 fatty acids, that acts as a mediator of inflammatory responses. DHA and EPA are omega-3 fatty acids commonly found in fish and fish oil.  Krill oil is another important source of DHA and EPA. 

Source: C. Tabak, A.H. Wijga, G. de Meer, N.A.H Janssen, B. Brunekreef and H.A. Smit. Diet and asthma in Dutch school children (ISAAC-2). Thorax; Volume 61, Pages 1048-1053, doi:10.1136/thx.2005.043034.

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