THURSDAY, May 5 (HealthDay News) -- Babies who are still drinking from a bottle at 2 years of age may be prone to obesity by the time they turn 5, a new study suggests.

For the study, researchers analyzed data on 6,750 children who participated in the Early Childhood Longitudinal Study, Birth Cohort, which included kids from around the United States born in 2001.

About 22 percent of the children continued to use bottles regularly at 24 months of age, meaning they mainly drank from a bottle or were put to bed with one.

At age 5 1/2, about 23 percent of the children who drank from a bottle at age 2 were obese, compared to about 16 percent of kids who'd stopped using a bottle by age 2, according to the study.

That makes children still using a bottle at age 2 about 33 percent more likely to be obese than children who were weaned sooner, the researchers said.

One likely explanation for the finding: kids who are still drinking from a bottle at age 2 are probably consuming more calories than they need, the study authors said.

"At older ages, the bottle is probably used for comfort and convenience rather than nourishment," said study lead author Rachel Gooze, a doctoral candidate in public health at Temple University's Center for Obesity Research and Education in Philadelphia.

The study will be published in an upcoming issue of The Journal of Pediatrics.

Children were considered obese if their body mass index [BMI, a ratio of weight to height] was at or above the 95th percentile for their age. The proportion of 5-year-olds in the study who were obese roughly tracked other national statistics that place obesity rates among pre-schoolers at about one in five, Gooze said.

Experts have long encouraged parents to wean children from the bottle around age one.

The American Academy of Pediatric Dentistry advises parents to wean children from a bottle at about ages 12 to 14 months, and to avoid putting a baby to bed with a bottle to avoid tooth decay.

The American Academy of Pediatrics has a similar recommendation, cautioning that "the bottle [should] be given up entirely at around age one and almost certainly by eighteen months."

Other research has suggested that prolonged bottle use may contribute to iron deficiency, according to background information with the study.

For the study, the researchers accounted for other factors that could influence obesity in 5-year-olds, including having an obese mother, socioeconomic status, whether kids were breast-fed as infants, and the timing of the introduction of solid foods. (They did not have information on the children's physical activity.)

Even when controlling for those factors, children who drank from a bottle at age 2 were more likely to be obese than kids who'd graduated to a cup, the researchers said.

Bottle-feeding or breast-feeding infants is necessary during the first year of life to provide adequate nutrition during a time of rapid growth, said Dr. Roya Samuels, a pediatrician at the Steven and Alexandra Cohen Children's Medical Center of New York.

Between 4 and 6 months of age, babies should begin eating solid foods, which will gradually become the child's main source of nourishment, Samuels said. A typical 1-year-old needs only about 10 to 16 ounces of whole milk per day, in addition to a "healthy assortment of table foods," she said. Parents should limit fruit and vegetable juices to no more than 4 ounces a day and the remainder of liquids consumed should be water, she added.

"If parents continue bottle-feeding into the toddler period, it is likely children will be consuming too many calories during the course of the day, leading to excessive weight gain into childhood," Samuels said, noting that this new study is among the first to track children over time to determine how prolonged bottle use may affect their weight.

Wresting a bottle away from an opinionated and stubborn toddler isn't easy, especially if there is a younger sibling in the house who is getting a bottle.

Gooze recommends that parents discuss weaning strategies with their pediatrician, and also change their own mindset about the transition. Rather than think of weaning as taking something away from the child, look at it as a sign your baby is reaching another milestone, she said.

"We definitely recognize stopping the bottle at a year of age is not easy, and stopping it at 2 years of age may be even harder," she said. "It might be helpful to think of moving from a bottle to a cup as a developmental milestone, like moving from crawling to walking, which is something to celebrate, even if it has challenges."

More information

The Nemours Foundation has tips for making the transition from bottle to cup.