Children who are breastfed do not get increased protection from developing asthma or allergies, new research claims.
A study in Canada that monitored 13,000 women and children found no evidence of a beneficial effect.
Researchers looked at babies born in 1996-97, and published their findings ahead of print in the British Medical Journal (BMJ).
The new mothers and babies were split into two groups, with one side being actively encouraged by hospitals and clinics to breastfeed, while the other saw clinicians carry on with their normal practices.
The first group saw a large increase in the number of women breastfeeding exclusively at three months, and they also breastfed for longer.
The researchers later tested the children at the age of six for asthma and house dust mite, cat, birch pollen, and mixed grass allergies, but found little difference.
Dr Michael Kramer, from The Montreal Children's Hospital, said: "Whether breastfeeding protects against the development of allergy and asthma has been frequently studied and hotly debated for more than 70 years.
"These results conflict with some previous studies suggesting that prolonged and exclusive breastfeeding reduces the risk of asthma, other allergic diseases, and atopy skin tests.
"On the other hand, the evidence is far from uniform, and several recent studies have even found breastfeeding (or more exclusive and prolonged breastfeeding) to be associated with increased risks of these outcomes."
"This is article comes across as anti-breastfeeding. It only looks at one area of health yet implies breast feeding to be a danger to health. Almost all of the women I look after breast feed their babies for various reasons. There are benifits of breastfeeding in many areas including reducing obsity rates and breastfeeding promotes good attachment between mother and baby. Research shows well attached children are less likely to display antisocial ehaviour in society (so fewer asbos!). There are health benifits for mum too" - Caroline Gill, Midwife, Staffordshire Moorlands Rural Children's Centre