Essential microbes: Babies born by Caesarean section may be more likely to develop allergic diseases than naturally-born children because they are less exposed to their mother's healthy bacteria during birth, according to a leading Finnish paediatrician.
Speaking in Dublin at a conference on bacteria in health and food, Prof Erica Isolauri said exposure to non-pathogenic bacteria during birth strengthens a person's immune system in later life and reduces the chances of allergies such as dermatitis, rhinitis and asthma.
"Have you ever wondered why children come to the world through the most bacterial-rich environment? Why don't they simply get out through the abdominal wall in a sterile situation?" she asked.
Caesarean section affects the early colonisation of the gut by bacteria, and thus delays immune system development, she said.
"There are five studies showing an association between Caesarean sections and asthma and atopic disease and one reason could be the delay in intestinal colonisation," Prof Isolauri said.
Atopic diseases are allergies in which the sufferer has a constitutional tendency to develop hypersensitivity reactions to allergens.
If the first step in the development of the immune system - birth - is disturbed it affects "the next and the next, step by step towards adulthood", said Prof Isolauri.
Birth is the earliest micro-biological exposure in life, she said. "It has the most massive bacterial load. As you are born the first colonisation is from the mother."
The first few months of life are also important in the bacterial colonisation of babies' intestines. "Maternal bacteria and breast milk affect colonisation," said Prof Isolauri.
The type of microbes in a baby's intestine are key determinants of the immune profile of the infant, she said. "By three months of age much has happened."
Babies are very responsive to manipulation of their intestinal microbe levels with probiotics, whereas adults are not, she said.
Prof Isolauri stressed the importance of good diet during pregnancy: "The maternal diet during pregnancy affects the quality of breastmilk after a baby is born."
Retrospective studies show a clear relationship between nutrition in early life and the likelihood of developing atopic diseases, she said.
"During the war years women who were pregnant were sent to the countryside and their nutritional environment was very different. Their children had less asthma and atopic diseases."
Prof Isolauri heads a research team called NAMI - Nutrition, Allergy, Mucosal-immunology and Intestinal microbiotic - at the University of Turku, which is multi-disciplinary and includes immunologists and nutritionists. She has received numerous academic honours for her work.
Prof Isolauri said her research was building on the "hygiene hypothesis", the notion that we've made our environment too hygienic for our own health.
More than 10 years ago British epidemiologist David Strachan looked at 17,000 British children and found that the more older siblings a child had the less likely he or she was to develop hay fever, suggesting that greater exposure to infections reduces the risk of allergy.
She also referred to German research into allergy and asthma rates before and after reunification, showing the effects of westernisation. Before 1989 East Germans had more respiratory infections and less allergies than their western neighbours. After unification rates of allergies in the East increased.
In Estonia, the move to a western lifestyle, which includes eating processed foods, had a similar effect, said Prof Isolauri. "Processed food affects our immune system. When you eat processed, ready-made and sterilised food you still need microbial exposure and fresh produce."
Other lifestyle determinants of allergy are bacteria-poor sterile environments and an urban lifestyle.
Along with smaller family sizes and increased rates of Caesarean section, immune systems are now more compromised, she said.