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Consumption of milk fat and reduced asthma risk in pre-school children.

We read the paper by Wijga et al 1 published in the July 2003 issue of Thorax with great interest. The authors found that the consumption of specific food items such as full cream milk, butter, and brown bread can contribute to a decrease in the risk of asthma and wheezing in pre-school children. These findings agree with previous studies in adults,2 but there are a few methodological problems in the analyses used in the study which may have influenced the results obtained.

Our first area of concern is that trans-generational traditions of families with atopic diseases are not taken into consideration. For instance, families with a history of atopy tend to smoke less, which is described as a “healthy passive smoker effect”.3,4 Grandparents and parents who have asthma tend not to smoke, but their children are more likely to develop atopic manifestations than children from smoking families without asthma. It is also likely that atopic parents change their exposure to pets which may lead to a similar “healthy pet keeping effect”.5 For related reasons, families may also alter their diets resulting in a “healthy cow’s milk effect”. These potential changes within families are supported by avoidance strategies propagated by various national medical associations. Children of atopic parents therefore tend to experience different exposures. Hence, before using statistical models we need to investigate the extent to which the diet of children differs according to the atopic status of their parents. An additional table is therefore needed, comparable to table 2, with consumption frequencies in columns for allergic and non-allergic parents as well as “allergic mothers” …