If nearly all women worldwide breast-fed their infants and young children, there would be about 800,000 fewer children's deaths and 20,000 fewer breast cancer deaths a year, researchers report.
That decrease in children's deaths is equivalent to 13 percent of all deaths in children younger than 2 years of age, the study authors reported in a two-part series published online in The Lancet.
The researchers also said that current breast-feeding practices cost the world's economy hundreds of billions of dollars a year.
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"There is a widespread misconception that the benefits of breast-feeding only relate to poor countries. Nothing could be further from the truth," series author Cesar Victora, of Federal University of Pelotas in Brazil, said in a journal news release.
"Our work for this series clearly shows that breast-feeding saves lives and money in all countries, rich and poor alike. Therefore, the importance of tackling the issue globally is greater than ever," Victora added.
Only one in five children in high-income countries is breast-fed for 12 months, the researchers said. And, only one in three children in low- and middle-income countries is exclusively breast-fed for the first 6 months.
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This means that millions of children and women don't receive the full benefits offered by breast-feeding, which has been shown to be healthy for both mothers and children, the study authors said.
In a detailed worldwide analysis, the researchers identified a number of benefits of breast-feeding. For example, breast-feeding lowers the risk of sudden infant death in high-income countries by more than one-third, they said.
The study also found that breast-feeding could prevent about half of all cases of diarrhoea and one-third of respiratory infections in low- and middle-income countries.
Breast-feeding reportedly also boosts children's intelligence and may protect them against obesity and diabetes later in life, the researchers said. Among mothers, long-term breast-feeding reduces the risk of breast and ovarian cancer, the researchers added.
Read: Breast-feeding may protect infants against obesity
The investigators also estimated that poorer thinking skills among children who aren't breast-fed cost the global economy about $302 billion in 2012. The loss in high-income countries alone was $231 billion, the study concluded.
Increasing breast-feeding rates for infants younger than 6 months to 90 percent in the United States, China and Brazil, and to 45 percent in the United Kingdom, would lower treatment costs of common childhood illnesses such as pneumonia, diarrhoea and asthma.
Despite the many benefits of breast-feeding, rates are low, especially in high-income countries, the study showed.
"Breast-feeding is one of the few positive health behaviours that is more common in poor than richer countries, and within poor countries, is more frequent among poor mothers," Victora explained.
Read: Low breast-feeding rate linked early deaths
"The stark reality is that in the absence of breast-feeding, the rich-poor gap in child survival would be even wider. Our findings should reassure policymakers that a rapid return on investment is realistic and feasible, and won't need a generation to be realised," he said in the news release.
Reasons for low breast-feeding rates include poor promotion and support of breast-feeding, and aggressive marketing and rising sales of infant formula, the study authors said.
"There is a widespread misconception that breast-milk can be replaced with artificial products without detrimental consequences," Victora said.
"The evidence outlined in the series, contributed by some of the leading experts in the field, leaves no doubt that the decision not to breast-feed has major long-term negative effects on the health, nutrition and development of children and on women's health," Victora concluded.
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