Junkfood Science: Turning down the child care alarm

July 26, 2008

Turning down the child care alarm

At every turn, new parents are being given another worry. This month, news has been reporting that babies cared for by people other than their parents gain more weight. A new study was reported as finding babies placed in day care, even in the care of a relative, were more likely to be fed improperly.

Almost instantly, mothers who had to go back to work or school after their maternity leaves, and unable to stay home with their babies, were being guilted out. Speculations as to why babies in child care might gain more weight ran from mothers not breastfeeding to caregivers more likely to pacify an irritable baby with milk or to give solid foods too early. The study, however, provided no evidence to support such assumptions, so before any more blame is directed at parents for having fat babies, let’s look at the study and the information media didn’t report.


Published in Archives of Pediatrics and Adolescent Medicine, this paper was not reporting the results of a randomized intervention trial, but an epidemiological study that had looked for correlations among part of a database of babies who had been enrolled in the Early Childhood Longitudinal Study, Birth Cohort study. The 14,000 children participating in the ECLS study were a representative sample of babies born in 2001 in the United States, with an oversampling of Asian and Pacific Islanders, American Indians, twins, and infants with moderately low and very low birth weight.

During October 2001 and December 2002, the ECLS team had done home visits of 9 month-old babies and gathered information, which included the following things used in this analysis:

· Parents had been asked about child care, including the type, hours in care, and the age when the baby first entered care. No child care providers or facilities were actually evaluated.

· Parents had also been asked when solid foods (referring to cereal and baby food in jars) were introduced, but there were no records on how often, the amount, or type of solid foods any of the babies had consumed.

· Babies’ lengths were measured and, using a bathroom scale, the mothers were weighed holding their baby and then the mothers’ weights were subtracted. The imprecision of bathroom scales, of course, lends caution to interpreting small variations.

For this analysis, Dr. Juhee Kim of the University of Illinois at Urbana-Champaign and co-investigator Dr. Karen E. Peterson of Harvard School of Public Health, Boston, selected 9,650 babies, 8 to 14 months of age, from the ECLS database. No explanation was given for why 4,350 babies were eliminated from the original study population. They further eliminated babies born to mothers younger than 15 years old and those under 32 weeks gestation; and another 6% for inadequate data. They conducted their analysis on 8,150 babies — 58% of the original ECLS participating children.

Using statistical modeling, the authors looked for correlations between weight gain, child care and introduction of solid foods among this data.

The babies in full-time day care differed from the other babies in several notable ways. A higher percentages of babies in full-time day care had been preemies or low birthweight babies. The babies who had been placed in child care earliest and more likely to be in full-time day care were also more likely to be black, with full-time working mothers, or unmarried mothers.


By 9 months of age, more than half of the babies in this cohort were in child care, most with relatives. Of those, about half were in child care full-time.

Months in child care. About 22% of the babies had been placed in child care before 3 months of age and these were the babies who gained the most weight during their first year of life. And the babies who had been in child care the fewest number of months (who didn’t begin child care until they were 6-11.9 months of age) or those who were cared for by their parents, gained the least.

But stop the presses: it was a difference of 8 grams — 0.2 ounces. Less than the weight of a baby poop.

Full-time versus part-time in child care. Weight gains associated with babies cared for by their parents were lowest (6001 grams), followed by those in day care part-time (6159 grams) and full-time (6190 grams). This was a difference in the raw (unadjusted) data of 6.6 ounces over the first year. But wait: before you jump to conclude it was the child care, remember those other correlations.

More of the babies in full-time child care were preemies or low birthweight babies. In other words, these were the babies with different growth patterns and more likely to gain more weight and to exhibit catch-up weight gains during the first few years of life. Higher weight gains among these babies could be a healthful sign and reduce their morbidity and mortality, not a negative. “Premature infants with intrauterine growth retardation and no catch-up growth have a higher risk of developmental delay and other medical problems than premature infants with a normal growth rate,” explained doctors David Trachtenbarg, M.D., and Thomas Goleman, M.D., in a recent issue of American Family Physician.

Regrettably, we have no information on the health or specific birthweights of the babies used in this analysis. The babies in full-time day care were, however, more likely to be born to black mothers with higher maternal weights. Pediatricians, knowing weights and heights are largely genetic, anticipate babies to take after their parents and grow larger. These authors recognized this genetic fact and factored for it in their analysis of odds ratios coming up...

Growth and development. Reports have been quick to assume that the greater weight gain among the day care babies, even as nominal as it was, was a bad thing. Not a single reporter stopped to consider the possibility that it was healthful, normal for those particular babies and a good sign. The quick assumption has also been made that this weight gain meant “overweight” or babies that were too fat. But we have no information on where any of the babies fell on their individual growth curves or if they were gaining more than would be anticipated given their birthweight, health and family genetics. Medical professionals compare each baby’s growth to how they follow their individual growth curve, not compared to other babies by pounds and ounces.

Variations among lengths and weights of babies naturally fall into a range, similar to the bell curve. But about a third of a pound difference in weight gain over a year among all of the babies in this cohort, however, does not an “overweight” baby make. Nor do variations in childhood growth patterns predict adult obesity, as has been covered extensively.

The authors reported that only birthweight was a significant factor in weight gain among the other correlations. No breakdowns were provided. But here they are also describing that large term babies, for example, even while gaining the same percentage of body weight as smaller babies, would naturally gain more weight when measured in pounds and ounces. Once again, each baby’s growth and development can only be evaluated using his/her individual growth curve.

Solid foods. The feeding data used in this data dredge were pretty crude measures — parental reports only of the age solid foods were begun and if breast feeding had been initiated. As this study shows, it’s easy to make assumptions about causations from correlations... assumptions that aren’t supportable.

There was only one tenable odds ratio reported in the entire study. Among the correlations between feeding practices and types of childcare, the preterm or low birthweight babies were three times more likely to have been introduced to early solid foods in daycare settings (RR=3.18, CL 1.27 to 5.08).

But there was no consistent relationship between early solid foods and when babies were placed in childcare (at birth, 3 months or 6 months of age). Underweight babies starting daycare at 3-6 months of age were no more likely to have begun solid foods early than those cared for by their parents. Once again, we can’t jump to conclude that child care was at fault.

Reflux, for example, is not uncommon in premature or small babies and some pediatricians recommend cereal to help reduce their symptoms. There were no other details provided about the small babies placed in childcare, their health conditions, or what the care providers may have been asked to feed these babies when placed in their care.

And remember, none of the babies’ actual dietary intakes were measured or followed, so we have no idea what or how much any of them really ate. Instead, a lot of groundless assumptions have been flying around, insinuating that child care workers were force feeding babies to pacify them.

So, while an association was reported between the age when solid foods were introduced and weight gain, and babies in child care (in a cohort of higher percentages of preemies and low birthweight babies) had higher odds for early introduction of solid foods, the authors were quick to add: “However, we found no mediating role for early introduction of solid foods in the hierarchical regression models of weight gain.”

They also reported “no effect of introduction of solid foods on weight gain among preterm and LBW infants. We were not able to show the potential mediating role of infant feeding practices between the observed risk of child care and weight gain.”

Breast feeding. The initiation of breastfeeding and child care naturally correlated, as mothers having to go back to work or school and needing to place their babies in the care of others during the day are less likely to breast feed. But, that doesn’t necessarily mean that it was the breastfeeding that explained the slightly lower weight gains among the stay-at-home babies. As the authors wrote: “We found no protective effect of breastfeeding on weight gain.” Nor was breast feeding and solid foods predictive of weight gain.

As they wrote:

We found no interaction between breastfeeding initiation and early introduction of solid foods in predicting weight gain. Findings were consistent with lack of association of breastfeeding initiation to weight gain among all infants and term and NBW infants, whereas breastfeeding initiation was associated with less weight gain among preterm and LBW infants.

Media has been quick to suggest that the association between child care and infant weight gain is evidence mothers should breastfeed to prevent obesity in their children. Not only did they not read the study, but the body of evidence has never supported this widespread belief. As with all transient changes in health indices, they are not predictive of actual or long-term clinical outcomes. Breastfed babies have different growth curves in infancy, with no effect on later body weights. Weight or diet in infancy or childhood is not predictive of adult body weight.

· The World Health Organization-Food and Agriculture Organization of the United Nations (FAO) 2003 report, Diet, Nutrition and The Prevention of Chronic Disease, noted that most of the 20 studies, involving 40,000 babies, that have examined the role of breastfeeding in overweight have found no relationship. It’s easy to be led astray by failing to consider confounding factors, such as genetics and socioeconomics, among studies in developed and underdeveloped countries.

· Two studies published in the October 2003 issue of the British Medical Journal concurred. One, funded by WHO and Canada’s International Development Research Centre, was released as “the largest such study done in the developing world.” It followed 2,584 babies born in 1958 for 33 years and found no association between breastfeeding and adult weights. Breastfeeding did not protect against obesity later in life. The researchers added: “Secular trends do not suggest a protective effect: in both Britain and the United States the incidence of breast feeding has increased since 1990, but so has obesity.

· The recent study of 240 fat Latino young people led by Dr. Jaimie N. Davis, Ph.D., at the University of Southern California, Los Angeles, found no protective effects of breastfeeding on adiposity or risk for type 2 diabetes.

· And an investigative study of the government’s promotion of breast feeding as a strategy for reducing childhood obesity, led by researchers at Harvard Medical School in Boston, followed 35,526 mothers and babies from 1989-2001. They also found no association between breastfeeding and risk for overweight or obesity in adolescence or adulthood, even among kids who were leaner at age 5. They concluded that breastfeeding “is unlikely to play an important role in controlling the obesity epidemic.”

New parents are surrounded by people eager to tell them how best to care for their babies or quick to criticize them for not doing something right. The trouble is, few pop beliefs or media stories are true or give the full story. Loving parents deserve to trust that when they make decisions they feel are best for their babies and families, they most likely are.

© 2008 Sandy Szwarc

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