By Jeremy Laurence, The New Zealand Herald
Just when we thought scientists had made their minds up on a topic - from life on Mars to the health dangers of bacon butties - another study comes along to upset the consensus.
This week, researchers reported that breastfeeding babies boosted their IQs by seven points. But this occurs only in babies who inherit a gene called FADS2.
Nine out of 10 children have the necessary gene. For the one in 10 who doesn't, breastfeeding makes no difference to intelligence. Bottle-feeding, in this regard, is equally good.
Is this the last word on the subject? Probably not. The link between breastfeeding and intelligence has been debated since 1929 when the first paper on the subject was published. We thought we had heard the last word a year ago when the largest scientific study of the supposed link concluded that breastfed babies were indeed smarter - but not because of the milk they were fed.
Instead, the researchers from the University of Edinburgh, said they were smarter because their mothers were likewise. Women who breastfed tended to be more intelligent and more highly educated and provided more stimulation for their babies at home. The higher IQ of their babies was mostly inherited, accounting for 75 percent of the difference. The rest of the difference was because of their environment - breastfed babies had mothers who were older, better-educated and lived in nicer homes, where the the children received more attention.
Terrie and Abshalom Moffit, the husband and wife team who published this week's study based on 3 000 children in Britain and New Zealand, said they had corrected for these factors - and they still found a seven-point IQ difference.
Is a higher IQ the main benefit? No. There are many others, from improving bonding between mother and baby immediately after birth to boosting the baby's immune system through delivery of colostrum, the first antibody.
This is the rich, thick yellowish milk produced in small quantities before the mature milk comes in. Breastfeeding is thought to protect against infections and allergies, reducing the risk of asthma and eczema in childhood. It also reduces the risk of diabetes, high blood pressure and obesity in adulthood. Other advantages: it delivers the right balance of nutrients, at the right temperature; it is convenient, quick and costs nothing, unlike formula milk; it protects the mother - mothers who breastfeed have a lower risk of breast cancer.
Are the pressures to breast-feed growing? There is a certain amount of political correctness among breastfeeding advocates that brooks no opposition. The result is women who cannot or will not breastfeed end up feeling guilty.
Parenting websites are full of tales of women upset by unsympathetic friends, nurses or doctors when they failed this test of motherhood.
One is quoted as saying: "I was never able to breastfeed Charlie as my milk was making him sick and we were told by the doctors to stop breastfeeding. He was in intensive care and was tube-fed for the first eight weeks. Then I was told yesterday by a doctor that the reason Charlie gets sick now is that he wasn't breastfed and it is my fault."
What puts women off it? All sorts of reasons, from discomfort to difficulty producing sufficient milk to fears about physical appearance. A common reason cited is that the baby rejected the breast. Breastfeeding is a skill that needs to be learned, and often these difficulties can be overcome with a little help and support at the start.
The main reasons women stop breastfeeding early (within six weeks) are that they have insufficient milk, the process is too long or too tiring, or they have returned to work. The support of friends and relatives is crucial to whether women continue. Nine out of 10 women who stopped breastfeeding within six weeks say they would have liked to continue for longer.
Formula milk is bad for babies, isn't it? It depends where you live. For most of us in the West, formula milk is a perfectly adequate substitute for breast milk if the real thing is not available. In the developing world it is different.
Where access to clean water with which to mix the powdered formula is a problem, bottle-feeding can be a killer because it exposes the baby to bacteria causing diarrhoea and other diseases. That is why breast has been promoted in the developing world as best and the formula milk manufacturers have been accused of overselling their products with heavy marketing campaigns which have undermined this vital message.