Parliament's health committee chairwoman Steve Chadwick has joined critics of a study that has found breast-fed babies more susceptible to allergies and asthma.

The report, compiled using data from Otago University's ongoing multidisciplinary study, tracked the health of more than 1000 children born in 1972 and 1973 in Dunedin.

It found that 13-year-olds breastfed as babies were almost three times more likely to have asthma than those who were bottle-fed.

Ms Chadwick, a former midwife, said the study was unhelpful at a time when health professionals were trying to encourage women to breast-feed for longer. She said it was inconclusive and disturbing.

Ms Chadwick managed a maternity and children's service at Lakeland Health in Rotorua before becoming an MP in 1999.

"The summary of the study itself specifies breast-fed babies as those who were breast-fed for four weeks or longer," she said.

"Four weeks is not a long enough time to draw any conclusive results, and I would be keen to know how many of those so-called breast-fed babies were exclusively breast-fed."

She said breast-feeding was safer, cheaper and more nutritional than bottle feeding, and it reduced early childhood illnesses.

The Australian Breastfeeding Association president Anne Croker said yesterday that the study would scare vulnerable new mothers.

Plunket New Zealand expressed similar concerns last week.

Ms Croker said: "The critical point is that measurements for a study of this kind need to be based on what the World Health Organisation defines as exclusive breastfeeding, which means the baby feeds only on mother's milk.

"The baby has no cow's milk or formula.

"Given that the New Zealand study admits its cohort of children were not exclusively breast-fed for at least their first six months, then the utmost caution should be used before anyone tries to claim causal links."

She called on Australian health authorities to publish a search of scientific literature to reinforce the benefits of breastfeeding babies.

But the report authors, from McMaster University in Canada as well as Otago, make it clear breastfeeding has many benefits, including optimum nutrition and reduction of risk of infant infections.

"However, the role of breastfeeding in protection of children against atopy allergies and asthma cannot be supported on the basis of the present balance of evidence."

The report says that the findings, which were contrary to the researchers' original hypothesis, were strengthened by the long (26-year) period of regular follow-up reviews and allergy and asthma testing.

- NZPA