For Healthy Kids, Consider Bedtime and Bottle Size

Two new studies offer a few seldom-considered strategies for parents trying to raise healthy, physiotypical children.

A study from 2012 found that formula-fed infants were significantly more prone to weight gain than breast-fed babies, an outcome considered undesirable. Now, a 2016 study looking at the size of the bottles has concluded there is additional weight-gain risk, the larger the bottle used.

The phenomenon contributing to weight gain in the older study appears to be that babies who are bottle-fed do not learn, or can unlearn, self-regulatory eating behaviors that monitor satiety and cause the infant to stop when they are full. The outcome was the same—increased weight gain—regardless of milk type, and in fact babies consuming mother’s milk still gain more weight when the milk, although the exact same as milk from the breast, was given through a baby bottle.

The researchers followed nearly 1,900 mother-infant pairs over the course of one year. Compared with infants who were breast-fed, those who were bottle-fed gained 2.5 oz more per month when given nonhuman milk and over 3 oz more when given breast milk. Babies who received breast milk who were fed frequently by bottle gained more weight than those fed frequently at the breast.

In the new study, researchers looked at how the size of baby bottles may increase weight in just under 400 formula-fed infants.

Bottle size was determined at baby’s two-month visit, and weight and length were measured at the two- and six-month visits. Infants fed from 6-oz or larger bottles had significantly greater weight increases between the two visits than infants using smaller bottles—the weight difference between the two groups was 7.4 oz. Larger bottle size was also associated with significant increases in weight-for-age and weight-for-length z scores.

Guiding parents toward smaller bottles in early infancy is a simple step that could benefit babies by helping avoid overfeeding and rapid weight gain. The researchers conclude, “[B]ottle size may be a modifiable risk factor for rapid infant weight gain and later obesity among exclusively formula-fed infants.”

In yet another study published this year, early bedtime for preschool-aged children seemed to help prevent obesity in adolescence. Nearly a thousand U.S. children were enrolled at birth in this prospective cohort study during which bedtime was reported by mothers when children were of preschool age, and BMI was assessed later at age 15.

“Early bedtime” was considered bedtime before 8 p.m. At a mean age of 4.7 years, 25% of the children in the study had bedtimes at or before 8 p.m, 50% went to bed between 8 and 9 p.m., and another 25% were tucked in after 9 p.m.

Risk for adolescent obesity was reduced by half in children going to bed at or before 8 p.m., as compared to those with the later bedtimes of 9 p.m. or after. That is, Preschool-aged children with early weekday bedtimes were one-half as likely as children with late bedtimes to be obese as adolescents. The prevalence of adolescent obesity was 10% for the earliest bedtimes, 16% for the half of subjects in the 8 to 9 p.m. range, and 23% for those with the latest bedtimes.

Bedtimes are yet another modifiable routine that may help to prevent obesity, and pediatricians should not only encourage early ones, but, as the study authors put it, “support parents in their efforts to overcome the barriers they face in implementing this routine.”
Arch Pediatr Adolesc Med, 2012, Vol. 166, No. 5, pp. 431-6

Pediatrics, published online June 2016,

J Pediatrics, 2016,

(return to front page)