Mothers who breastfeed for six months or more halve their diabetes risk, according to major new research.

The 30-year study found that the longer mothers breastfed, the greater reductions they saw in their risks of developing type 2 diabetes. 

Breastfeeding has been linked to all manner of benefits for both mothers and their babies, including lower risks for ovarian cancer and heart disease for mothers, and better brain development and lower rates of obesity and asthma in their children.

The new research from Kaiser Permanente, however, is one of the largest and longest studies to demonstrate that breastfeeding may protect women against type 2 diabetes. Though men are more likely to develop type 2 diabetes later in live than women are, nearly 12 percent of American women are diagnosed with the disease and many as 27 million are considered prediabetic - numbers driven up by the country's continuing obesity epidemic.

A study conducted between 1971 and 2000 also found that women with diabetes had poorer survival rates than men with the same disease, which shortened life spans for women by 8.2 years, compared to healthy people. 

The new study's findings suggest that breastfeeding could help to close those health gaps.  

As of 2013, the majority of new mothers - about 77 percent - opted to breastfeed, according to data from the Centers for Disease Control and Prevention (CDC). 

Breast milk contains a cocktail of nutrients meant to perfectly meet the needs of a new baby. 

US agencies, including the CDC and the American College of Obstetricians and Gynecologists (ACOG) recommend that women breastfeed for at least the first six months of their babies' lives. 

It is not clear why the practice seems to have so many health benefits for women.

Scientists suspect that natural feeding's effects on hormones may have protective effects, and that choosing not to breastfeed may upset the balance of a woman's systems. 

The new research, spanning 30 years of data reported not just by the women themselves, but by their doctors, bolstered theories that breastfeeding may have  protective effects for women's metabolic functions.  

Lead study author Dr Erica Gunderson, senior research scientist with the Kaiser Permanente Division of Research said: 'We found a very strong association between breastfeeding duration and lower risk of developing diabetes, even after accounting for all possible confounding risk factors.'

Notably, diabetes risks were reduced for all races. 

In the US, black women are both more likely to develop type 2 diabetes and less likely to breastfeed than white women are, according to recent research.  

The results showed that women who breastfed for six months or more across all births had a 47 percent reduction in their risk of developing type 2 diabetes compared to those who did not breastfeed at all.

Women who breastfed for six months or less had a 25 percent reduction in their diabetes risk, according to the findings published in the journal JAMA Internal Medicine.

Dr Gunderson and her colleagues analyzed figures during the 30 years of follow-up from the Coronary Artery Risk Development in Young Adults (CARDIA) study, involving around 5,000 American adults who were aged 18 to 30 when they enrolled in the study in 1985.

She said the new findings add to a growing body of evidence that breastfeeding has protective effects for both mothers and their offspring, including lowering a mother's risk of breast and ovarian cancer.

Dr Gunderson said: 'The incidence of diabetes decreased in a graded manner as breastfeeding duration increased, regardless of race, gestational diabetes, lifestyle behaviors, body size, and other metabolic risk factors measured before pregnancy, implying the possibility that the underlying mechanism may be biological.'

She said several plausible biological mechanisms are possible for the protective effects of breastfeeding, including the influence of lactation-associated hormones on the pancreatic cells that control blood insulin levels and thereby impact blood sugar.

Dr Tracy Flanagan, director of women's health for Kaiser Permanente Northern California, said: 'We have known for a long time that breastfeeding has many benefits both for mothers and babies, however, previous evidence showed only weak effects on chronic disease in women.

'Now we see much stronger protection from this new study showing that mothers who breastfeed for months after their delivery, may be reducing their risk of developing type 2 diabetes by up to one half as they get older.

'This is yet another reason that doctors, nurses, and hospitals as well as policymakers should support women and their families to breastfeed as long as possible.'

Dr Gunderson added: 'Unlike previous studies of breastfeeding, which relied on self-reporting of diabetes onset and began to follow older women later in life, we were able to follow women specifically during the childbearing period and screen them regularly for diabetes before and after pregnancies.'