Nursing mothers who breastfeed for longer amounts of time may be helping their babies avoid weight troubles later in life, according to research.

Results gleaned from 17 studies over the last 39 years suggest an association between the number of months babies are breastfed and the risk of being overweight.

"One month of breastfeeding was associated with a 4% decrease in risk (of being overweight)," concludes Dr. Thomas Harder and colleagues in the study, published in the American Journal of Epidemiology. "These findings strongly support a dose-dependent association between longer duration of breastfeeding and decrease in (the) risk of (being) overweight."

Investigators analyzed numerous studies dating back to 1966 up to 2005, looking at overweight rates for children who were breastfed and those who were exclusively fed with formula. After nine months of breastfeeding, the effect on being overweight plateaued, the researchers found.

Study authors did not outline specific reasons for the linkage between breastfeeding and being overweight. But some researchers believe breastfed babies are more familiar with signals of "fullness" than formula-fed babies, prompting them to stop feeding.

"The mechanisms by which breastfeeding affects the risk of (being) overweight are still unclear," the study states. "(However), breastfeeding results in a lowered body weight gain during the critical neonatal periods, obviously caused by a lower mean caloric intake in breastfed infants, compared with formula-fed neonates ."

Scientific evidence has shown that breast milk contains all the essential nutrients and elements needed to nurture the healthy growth of a baby for the first six months of life. However, additional vitamin D supplementation is usually recommended by doctors for babies who are exclusively breastfed.

Breast milk is well suited for a baby's delicate digestive system and is rich in antibodies, which help fight off bacteria and viruses. The Canadian Paediatric Society recommends that all newborns be exclusively breastfed for the first six months of life and that the nursing can continue for two years or more.