They found that while 75 per cent of newborns get breastfed right after birth, mothers give up quickly even though guidelines call for babies to get at least some mother's milk for the first year of life.
Breastfed babies are less likely to be obese as they grow older and studies show a range of health benefits from breastfeeding.
Fighting childhood obesity is one of the main goals of President Barack Obama's administration.
The team from US Centres for Disease Control and Prevention (CDC) found that 43 per cent of US mothers were still breastfeeding at six months, and 22 per cent at a year.
Nearly 90 per cent of newborns in Utah get breastfed, ranging down to just 52.5 per cent in Mississippi, the CDC team found. "We need to direct even more effort toward making sure mothers have the support they need in hospitals, workplaces and communities to continue breastfeeding beyond the first few days of life, so they can make it to those six and 12 month marks," Dr William Dietz, director of CDC's Division of Nutrition, Physical Activity, and Obesity, said in a statement.
The American Academy of Pediatrics recommends newborns get nothing but breastmilk for the first six months of life, and that mothers continue to breastfeed as the child begins taking other food until at least the end of the first year and longer if desired.
Breastfeeding lowers a woman's risk of breast and ovarian cancer and the Academy estimates if more US women breastfed their babies, it could lower annual US health costs by US$3.6 billion.