May 5, 2011 -- Kids who regularly use a bottle at age 2 are more likely to be obese by the time they’re ready for kindergarten than those who switch to cups at younger ages, a study shows.
But many parents don’t appear to be following that advice.
The study, which has tracked nearly 6,750 children across the U.S. from the time they were born in 2001, found that nearly one in four toddlers was still a regular bottle user at age 2.
Researchers found that, compared to those who were weaned off a bottle earlier, 24-month-olds who were drinking from a bottle were about 30% more likely to be obese by age 5 1/2. That’s after adjusting for a host of things thought to influence the risk of obesity, such as mom’s body weight, breastfeeding, the family’s income level, and time spent watching TV or computer screens.
“This is an important study because it identifies a clear risk factor for childhood obesity,” says Karen Bonuck, PhD, a professor in the department of family and social medicine at Albert Einstein College of Medicine in New York.
How Bottle-Feeding May Add Pounds
Though it’s not entirely clear how bottles may be causing obesity, researchers have some theories.
“At older ages, the bottle is probably used for comfort or convenience, rather than nourishment,” says study researcher Rachel A. Gooze, MPH, a doctoral student in public health at Temple University in Philadelphia.
Gooze says by age 2 many kids are having meals and snacks at the family table. Calories they get from a bottle that’s tucked into a car seat or into bed at night are likely to be extra.
“If we think of a 2-year-old girl of average size who’s put to bed with an 8-ounce bottle of whole milk, she’d receive about 12% of her daily caloric needs from that bottle,” Gooze says.
If she has eaten well that day, those calories may be in excess, Gooze says.
Weight Gain After Bottle-Feeding
For the study, which is published in the Journal of Pediatrics, researchers analyzed data collected in the Department of Education’s Early Childhood Longitudinal Study, Birth Cohort.
Children were included in the study at birth and assessed at 9 months, 24 months, 4 1/2 years, and 5 1/2 years.
Parents were asked, at the 24-month interview, if the child primarily drank from a bottle, a sippy cup, or a regular cup. They were also asked whether they usually put the child to bed with a bottle. If the answer to either question was yes, the child was considered to be a regular bottle user.
At age 5 1/2, children were weighed and measured. If their height and weight put them above the 95th percentile on standardized body mass index (BMI) charts, they were classified as obese.
Mothers were asked if they had ever breastfed and, if so, the age the child stopped breastfeeding. They were also asked what age solid foods were introduced.
Of the 6,750 children included in the study’s results, 17.6% were obese at age 5 1/2.
Nearly one in four (22.3%) was a regular bottle user at 24 months of age.
The prevalence of obesity at 5 1/2 years was about 23% in regular bottle users compared to about 16% in children who were not using a bottle.
After adjusting their data to account for 13 factors that are thought to influence the risk of obesity -- including socioeconomic status, race, maternal education, mom’s weight, breastfeeding, age at introduction of solid foods, and birth weight, 2-year-olds who were regular bottle users were about 33% more likely to be obese than those who primarily drank from cups at that age.
“This is a well-done study,” Bonuck says. “The main caveat, and this is a limitation of a large national survey, is that it is hard to say exactly what or how much of the daily calories came through the bottle.”
Bonuck points out that bottles come in all different sizes and can be filled to different levels, something this study wasn’t able to take into account.
The researchers acknowledge a number of other things that were missing. They didn’t have data on children’s physical activity, for example, or specific aspects of diet -- like total daily calories, sugar-sweetened beverages in the diet, or information on whether or for how long infants were exclusively fed breast milk.
Previous studies have suggested that exclusive breastfeeding for six months or more may reduce the risk of obesity later in life.
Advice to Parents
“Prolonged bottle use has been shown to lead to tooth decay in children,” Gooze says. For that reason alone, she says, it’s a good idea for parents to try to follow existing guidelines.
The American Academy of Pediatric Dentistry states that infants should not be put to bed with a bottle and recommends that parents wean infants from bottles between 12 and 14 months of age.
Gooze says many toddlers find that parting with the comfort and security of a bottle can be difficult. But parents can ease the transition by reframing the bottle’s departure as a developmental milestone, something big kids don’t need.
Switching from milk or juice to water may also help, especially if the bottle isn’t replacing a meal.