"This study suggests that higher vitamin D levels at birth may protect against insulin resistance, which is linked to obesity," says researcher Susanna Y. Huh, MD, MPH, a doctor at Children's Hospital Boston and instructor of pediatrics at Harvard Medical School.
She presented the findings at the Obesity Society's 28th annual scientific meeting in San Diego.
Vitamin D, Baby's Obesity Risk: What's the Link?
''It's a fairly recent hypothesis that vitamin D affects the risk of obesity," Huh says. Evidence of the link has been accumulating in recent years, she says.
She evaluated the children at age 3, evaluating their body mass index and other factors.
She measured the hormone adiponectin, produced by fat cells. The more adiponectin, the leaner one tends to be, she says. "You tend to be more insulin sensitive."
Being more insulin sensitive -- as opposed to resistant -- reduces the risk of obesity.
"We found that higher levels of vitamin D were associated with higher levels of adiponectin in the blood at age 3," she tells WebMD.
"The correlation was only for the cord blood," she says. "We did not see a correlation during pregnancy. It may be that in this case perhaps having higher levels of vitamin D status around the time of birth is more important than during the second trimester."
"There is not a definite level of adiponectin that is good or bad," she says. "You can't say you need 'X' amount of adiponectin to not be at risk for obesity."
In her study, Huh found that more than half the women had blood levels of vitamin D considered by most experts to be too low. The link needs to be studied more, she says.
"Adiponectin at this early an age has not been extensively studied,'' she says, even though it is well established as a marker of insulin sensitivity.
Vitamin D and Obesity Risk
The vitamin D-obesity link is ''still evolving," says Connie Diekman, RD, director of university nutrition for Washington University in St. Louis, who reviewed the findings for WebMD.
This is another bit of research, she says, "but not the last study."
Pregnant women are already told to watch their vitamin D," says Diekman, who is immediate past president of the American Dietetic Association and on the advisory panel for the National Dairy Council.
How much vitamin D is enough?
The recommendation from the Institute of Medicine (IOM), which sets standards, is 200 international units (IU) a day for adults 18-50. "We think that's probably too low," Huh says. "Most people who work in vitamin D [research] think people should be taking at least 800 IU per day."
The recommendation on vitamin D is under study by the IOM, which expects to issue a report by November 2010.
In 2008, the American Academy of Pediatrics issued recommended intakes for vitamin D that surpass those of the IOM, advising a vitamin D supplement of 400 IU a day after birth for those babies partially or exclusively breastfed or those drinking less than 1,000 milliliters a day of vitamin D-fortified milk or formula.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.