Breastfeeding could cut the chance of breast cancer by up to one fifth, a major international study has found.
Research on more than 750,000 women found it was a “powerful strategy” to reduce the risk of cancer, especially the most aggressive types of disease.
Experts said thousands of cases of cancer could be prevented and lives saved if Britain improved rates of breastfeeding, which are the lowest in the western world.
Just half of mothers in the UK are nursing their child at six weeks, and just one per cent follow NHS advice to provide their child with breast milk only until six months, official figures show.
Previous studies have suggested that breastfeeding has a protective effect against cancer, but have suggested the impact is relatively small.
But the major study- which spanned four continents, and will be presented at San Antonio Breast Cancer Symposium in Texas – suggests the effects are far more dramatic.
The meta analysis of 27 studies found that breast feeding reduced the risks of invasive breast cancers by around 10 per cent in most cases – and up to 20 per cent for the most deadly types of disease.
The research, led by American cancer charities, with the Washington University School of Medicine and Mount Sinai Hospital, New York, found it not only protected against common types of breast cancer but against triple negative cancer, one of the most difficult to treat.
Breast cancer is the most common cancer in Britain, suffered by one in eight women, with more than 50,000 diagnoses and 12,000 deaths a year.
Researcher Dr Graham Colditz, Associate Director of Prevention and Control at Washington University School of Medicine’s cancer centre, said higher uptake of breastfeeding could potentially prevent tens of thousands of cases of cancer.
“Broader uptake of breast feeding and completing up to 12 weeks of breast feeding for each baby can significantly reduce the subsequent risk of breast cancer,” he said.
The study did not conclude what the optimum duration of breast feeding was, but the risks seemed to reduce the longer women continued, authors said.
“The closest we came to an average risk reduction is a 10 per cent reduction in risk of breast cancer for women who had ever breast fed a baby,” Dr Colditz said.
Experts said that not all of the reasons for the effect were known but that it seemed the high hormone levels required for lactation appeared to affect cell growth, protecting the breast from changes which increase the risk of breast cancer.
The fact women do not usually ovulate while producing milk is also understood to protect against cancer of the breast and ovaries.
The research examined 27 studies over three decades, involving 750,000 women, 36,000 of whom developed breast cancer.
It concludes: “Breastfeeding is a powerful strategy to reduce the risk of several aggressive breast cancer subtypes, with a relative risk reduction of approximately 10 per cent to 20 per cent, depending on receptor status.
Midwives said women should be given more help to persist with breastfeeding, in order to help their children and protect themselves.
Official NHS advice says mothers should give their children only breast milk until the baby is six months old, but just one per cent achieve this.
Latest figures from the Organisation for Economic Co-operation and Development comparing 21 countries show that at three months, UK rates are the lowest in the Western world.
The international comparisons from their 2009 report show 13 per cent of mothers in Britain exclusively breastfeeding at three months, a figure which has since risen to 17 per cent.
Last week, mothers ’groups criticised British attitudes to breast feeding, after Claridges asked a feeding mother to cover her child with a napkin, and Ukip leader Nigel Farage suggested those breastfeeding should “sit in the corner”.
Proportion of children who were exclusively breastfed at 3 around 2005 (OECD Family database)
Anees Chagpar, Associate Professor of Surgery at Yale Cancer Center, said: “It is fairly well accepted now that breast feeding is healthy for the baby and has benefits for reducing breast cancer risk.”
“When Britain has one of the lowest rates you have to ask the question why? Are British women educated enough about breast feeding, or are there other reasons or barriers getting in the way?”
Jacque Gerrard, director for England at the Royal College of Midwives, said: “The RCM is committed to supporting members to help women give every baby the best possible start in life.
She said breastfeeding provided a “unique opportunity for mother and baby attachment”.
“It is without doubt a positive way for a woman to give her newborn the best possible start in life, and support her own health at the same time,” she said.
Katherine Woods, from Breast Cancer Campaign, said the study clearly highlighted that breastfeeding can lower the risk of breast cancer for mothers.
She said: “More research is needed for us to better understand the connection and to find out which types of breast cancer it affects the most and why.”
Yinka Ebo, Health Information Lead at Breakthrough Breast Cancer, said there were many actions -including breastfeeding – that a woman could do to protect against breast cancer.
“There are many things a woman can do to help reduce her risk of developing the disease,” she said.
“These include maintaining a healthy weight, limiting the amount of alcohol you drink and being regularly physically active,” she said.