Nearly eight in 10 U.S. newborns are now breastfed for some length of time, according to new government data, a continuation of a healthful upward trend that began decades ago.

But that overall stat of 79.2 percent masks a a strangely large regional difference in breastfeeding that experts have some difficulty explaining. Four western states--California (92.8 percent), Oregon (91.9), Washington (91.8) and Montana (91.2)--have the highest breastfeeding rates in the nation, with Vermont (90.0) the only other state that reaches the nine-in-ten threshold.

Meanwhile, a handful of southeastern states fill the bottom rungs in the Centers for Disease Control and Prevention's annual report card on breastfeeding. Louisiana (56.9 percent), Kentucky (61.3), Mississippi (61.5), Arkansas (67.1) and Alabama (67.3) have some of the lowest breastfeeding rates in the country, with only West Virginia (59.3 percent), Delaware (65.7) and Missouri (67.9) also in that range.

"I don't know that we fully know" the reason for the significant difference in regional breastfeeding practices, said Larry Grummer-Strawn, chief of the CDC's nutrition branch. "It's a different the general population and among health professionals."

In the south, "you're much more likely to get advice from your physician that it doesn't matter that much," he said.

Source: Centers for Disease Control and Prevention

Another chart in the report issued Thursday offers some clues to the answer. It shows that hospitals in many of those same states have fewer lactation consultants and a smaller percentage of infants born at "baby-friendly facilities," as defined by the World Health Organization and United Nation's Children's Fund. But that statistic doesn't follow regional lines as closely.

Such hospitals also are less likely to put mother and child together immediately and more likely to offer infant formula, Grummer-Strawn said, despite near universal acceptance that breastfeeding is more healthful for child and mother.

"No one is going to say 'we don't think it really matters'...and yet you still find physicians who say 'well, I wasn't breastfed and I'm okay," he said.

Still, the overall progress is remarkable when you consider that in 1972, only 22 percent of infants were breastfed, according to this National Academy of Sciences report.

"Formula was being pushed on moms and physicians," Grummer-Strawn said. "There was a culture among physicians that science knows best and what we create in the lab must be good."

The current national breastfeeding rate drops to 49.4 percent at 6 months and 26.7 percent at 12 months, even though the American Academy of Pediatrics recommends that women offer infants only breast milk for the first six months, and continue to breastfeed (as other foods are introduced) for at least the first year.

The AAP cites "unequivocal evidence" that breastfeeding helps protect infants against diarrhea, infections of the ear, respiratory tract and urinary tract, type 1 and 2 diabetes, lymphoma, leukemia and Hodgkins disease. New mothers also benefit via decreased risk of breast and ovarian cancers and less postpartum bleeding, and they return to their pre-pregnancy weight sooner.

Grummer-Strawn said the drop-off reflects the continued existence of barriers to breastfeeding, especially in the workplace. "We need a society that's going to support breastfeeding," he said. "Breastfeeding is the norm in the United States and should be seen as the normal way to feed babies."

The CDC has set a goal of 81.9 percent of children breastfed by 2020, a rate that seems attainable given the current data. But its goal of 60.6 percent children still breastfed at the age of six months appears more difficult to achieve.

The United States isn't the only country to experience this wide variation in breastfeeding rates. An article on the site just last month found a more than 56.1 percent difference in breastfeeding rates in Britain, from 36.7 percent in Stoke-on-Trent to 92.8 percent in a section of southwest London.

Read more: on 16 breastfeeding controversies in honor of World  Breastfeeding Week.