The prevalence of asthma and allergic diseases has increased dramatically over the past few decades with the highest incidence occurring in children. Epidemiological and immunological studies suggest that dietary modification or supplementation in the fetal life could reduce the development of atopic diseases, while fetal under-nutrition could detrimentally affect the “programming” of the fetal lung and immune system. We recently observed a reduced risk of wheeze and atopy among children at age 6.5 years whose mothers had a high adherence to the Mediterranean diet during pregnancy¹. To our knowledge, this is the first longitudinal study to assess prospectively in a general population the impact on asthma and atopy outcomes in childhood of maternal adherence to the Mediterranean Diet during pregnancy and children’s adherence to this type of diet.

Description of a birth cohort study

The survey is a birth cohort study that started in 1997 in Menorca island, Spain². Four hundred and sixty children were included in the analysis after 6.5 years of follow-up. Maternal dietary intake during pregnancy and children’s dietary intake at age of 6.5 years were assessed by food frequency questionnaires, and adherence to a Mediterranean Diet was evaluated through a priori defined scores. During the follow-up, parents answered a questionnaire on a yearly basis (with interviewer) and reported all medical events over the preceding 12 months. Information on parental education, socio-economic background, marital status, maternal disease, parity, and children’s cigarette exposures (during mother’s pregnancy and at child’s age of 6.5 years) was obtained through questionnaires administered at pregnancy and at the follow up at 6.5 years. Four hundred and twelve children (412, 89.6%) underwent skin prick testing at 6.5 years of age using a series of 6 common aeroallergens. Maternal atopy to common aeroallergens was measured by skin prick tests performed six months after delivery.

Results from observations after 6.5 years

The prevalence of persistent wheeze, atopic wheeze, and atopy at age 6.5 years were 13.2%, 5.8%, and 17.0% respectively. One third (166, 36.1%) of the mothers had low quality of Mediterranean Diet during pregnancy according to the Mediterranean Diet Score, while the rest had a high score. Consumption of vegetables more than 8 times per week during pregnancy was found to be protective for persistent wheeze, and atopy. Similarly, fish intake more than 2-3 times per week and legumes intake more than once per week were inversely associated with persistent wheeze. In contrast, an increased intake of red meat (more than 3-4 times per week) showed a trend towards positive associations with persistent wheeze and atopic wheeze in offspring.

A high level of adherence to the Mediterranean diet was found to be protective for persistent wheeze, atopic wheeze, and atopy at 6.5 years of age. Maternal Mediterranean Diet during pregnancy was highly associated with the adherence to this type of diet during childhood but the two dietary scores did not interact between each other significantly. When we simultaneously included maternal and children Mediterranean Diet Index in the multivariate models, results remained very similar, showing an independent beneficial effect of maternal diet during pregnancy on wheeze and atopy at 6.5 years of age.

The results of the present study, indicating a protective effect of maternal adherence to the Mediterranean Diet during pregnancy in wheeze and atopy at age 6.5 years, probably reflect a high fetal exposure to several antioxidant compounds and their adverse effect on oxidative stress damage of lung tissues. Cereals (particularly whole grains) are rich in antioxidant compounds (ie vitamin E, phenolic acids and phytic acid) and there have been shown to have a protective effect against asthma in children^{3, 4}. Similarly, fruits, vegetables and legumes are known to be high sources of antioxidants (vitamins C, E, carotenoids, selenium, flavonoids) and they may therefore help to protect the airways against oxidative damage. Apart from the most widely known antioxidants, other compounds possess a marked antioxidant activity and other advantageous biological properties, such as oleuropein, hydroxytyrosol and other polyphenols present in olive oil, the principal component of Mediterranean Diet⁵. On the other hand, the polyunsaturated n-3 fatty acids eicosapentaenoic (EPA) and docosahexaenoic (DHA) found in fish oïl have anti-inflammatory effects and high intake during pregnancy has been associated with a reduced risk of allergic diseases in childhood ^6-8.

Although considerable advances in knowledge have been gained from studies focused on single nutrients or food items, these may fail to account for the interactions between nutrients, and they do not take into consideration that some nutrients are inter-correlated9. Thus, interest has shifted to the study of food groups and, more recently, dietary patterns that represent a broader picture of food and nutrient consumption and may therefore be more predictive of disease risk. Dietary patterns such as Mediterranean Diet account for cumulative and interactive effects among nutrients, reflect real-world-dietary preferences, and may be particularly suitable for analysis in asthma epidemiology where many dietary components could be related with the outcome of interest.