Study links Mediterranean diet in pregnancy to reduced asthma and allergy risk in children

Women who eat a Mediterranean diet during pregnancy could cut their children’s risk of developing asthma and allergy, according to a new study, the work, which was partly funded by the EU, is
published online by the journal Thorax.

The Mediterranean diet is characterised by high levels of plant foods such as fruits and vegetables, bread and cereals, legumes and nuts, as well as moderate amounts of dairy products and eggs.
Fish is also consumed regularly, and this, along with olive oil, provides the main source of fat in the diet. Red meat is only eaten in small amounts. A number of studies have linked the
Mediterranean diet to lower levels of obesity, high blood pressure, coronary heart disease and various forms of cancer.

In 2007, some of the scientists involved in this study published research showing that a Mediterranean diet in childhood protects against allergic rhinitis and asthma symptoms. However, until
now, no-one has looked at the impact of a Mediterranean diet during pregnancy on the incidence of allergy and asthma in their offspring.

The researchers studied over 450 mother and child pairs living on the Spanish island of Menorca, from pregnancy until up to six and a half years after birth. Food frequency questionnaires were
used to assess the mother’s diet during pregnancy and the child’s diet at age six. During the follow up, the parents also provided information on their child’s respiratory and allergic
symptoms, and the children were tested for their response to six common allergens, including grass pollen and cat epithelium.

The mother’s diet during pregnancy was scored from zero to seven, depending on how closely she adhered to a ‘traditional Mediterranean diet’. One point was given for each component of the diet
that was consumed in above average amounts (vegetables, legumes, fruits and nuts, cereal, fish and dairy products). As meat is presumed to be detrimental, women who ate less meat than average
gained an additional point. A score of four to seven was regarded as a high quality Mediterranean diet.

The questionnaires revealed that almost two-thirds of the women ate a high quality Mediterranean diet during pregnancy.

At the age of six, just over 13% of children had persistent wheezing; 17% had positive reactions to skin test allergens; and almost 6% had asthma-like symptoms plus positive skin test results.

The scientists found that women who stuck to a high quality Mediterranean diet during pregnancy were significantly more likely to have children free of asthmatic symptoms and allergies than
women who ate a low quality Mediterranean diet. The influence of the mother’s diet was shown to be independent of the positive effects of a Mediterranean diet during childhood.

Components of the diet which seemed to have a particularly strong effect included eating vegetables more than eight times a week, eating fish at least three times a week, and having at least
one portion of legumes a week. In contrast, consumption of red meat three to four times a week seemed to increase the risks.

The scientists note that further studies are needed to understand exactly why a Mediterranean diet has such a clear protective effect against asthma and allergy. However, they note that the
results of their study ‘probably reflect high foetal exposure to several antioxidant compounds and their adverse effect on oxidative stress damage of lung tissues’.

Cereals, fruits, vegetables and legumes are all rich in antioxidant compounds such as vitamins C and E. Olive oil also contains antioxidants and has other advantageous properties. Meanwhile the
fatty acids found in fish oils have anti-inflammatory effects.

The researchers also highlight the importance of the window of exposure to these important compounds. In systems which take a long time to develop, such as the respiratory and immune systems,
the benefits of antioxidant compounds could be greatest at the very earliest stages of development, while the child is still in the womb.

‘As a result, the protective effect of a Mediterranean diet on the development of asthma and allergies could be higher during pregnancy than during childhood,’ the scientists write. ‘This is
consistent with our results that indicate a stronger and independent effect of maternal adherence to a Mediterranean diet during pregnancy on persistent wheeze and atopy rather than childhood
diet.’

Again, more research is needed to identify the most relevant window of exposure, and also to determine if the protective effects of the mother’s diet during pregnancy continue into later
childhood.

EU support for the research came from the NewGeneris (‘Newborns and genotoxic exposure risks’) and GA2LEN (‘Global allergy and asthma European network’) projects, both of which are funded under
the ‘Food quality and safety’ thematic priority of the Sixth Framework Programme (FP6).

For more information, please visit:
https://thorax.bmj.com/