Breast-feeding Benefits Appear to be Overstated, According to Study of Siblings
The NLSY79 is conducted by Ohio State’s Center for Human Resource Research for the U.S. Bureau of Labor Statistics.
Colen analyzed three samples: 8,237 children, 7,319 siblings and 1,773 “discordant” sibling pairs, or children from 665 surveyed families in which at least one child was breast-fed and at least one other child was bottle-fed. The children who were differently fed in the same family represented about 25 percent of the siblings in the data.
For each sample, the researchers sought answers to two basic questions: Was at least one child breast-fed and, if so, what was the duration of breast-feeding?
The study measured 11 outcomes that are common to other studies of breast-feeding’s effects: body mass index (BMI), obesity, asthma, hyperactivity, parental attachment (secure emotional relationships between parents and child) and behavior compliance, as well as scores predicting academic achievement in vocabulary, reading recognition, math ability, intelligence and scholastic competence. Colen constructed statistical models for the analysis.
Benefits to the Mother
Studies indicate that breastfeeding helps improve mothers’ health, as well as their children’s. A woman grows both physically and emotionally from the relationship she forms with her baby. Just as a woman’s breast milk is designed specifically to nourish the body of an infant, the production and delivery of this milk aids her own health. For example:
Breastfeeding helps a woman to lose weight after birth. Mothers burn many calories during lactation as their bodies produce milk. In fact, some of the weight gained during pregnancy serves as an energy source for lactation.
Breastfeeding releases a hormone in the mother (oxytocin) that causes the uterus to return to its normal size more quickly.
When a woman gives birth and proceeds to nurse her baby, she protects herself from becoming pregnant again too soon, a form of birth control found to be 98 percent effective—more effective than a diaphragm or condom. Scientists believe this process prevents more births worldwide than all forms of contraception combined. In Africa, breastfeeding prevents an estimated average of four births per woman, and in Bangladesh it prevents an estimated average of 6.5 births per woman.
Breastfeeding appears to reduce the mother’s risk of developing osteoporosis in later years. Although mothers experience bone-mineral loss during breastfeeding, their mineral density is replenished and even increased after lactation.
Diabetic women improve their health by breastfeeding. Not only do nursing infants have increased protection from juvenile diabetes, the amount of insulin that the mother requires postpartum goes down.
As expected, the analyses of the samples of adults and their children across families suggested that breast-feeding resulted in better outcomes than bottle-feeding in a number of measures: BMI, hyperactivity, math skills, reading recognition, vocabulary word identification, digit recollection, scholastic competence and obesity.
When the sample was restricted to siblings who were differently fed within the same families, however, scores reflecting breast-feeding’s positive effects on 10 of the 11 indicators of child health and well-being were closer to zero and not statistically significant - meaning any differences could have occurred by chance alone.
The outlying outcome in this study was asthma; in all samples, children who were breast-fed were at higher risk for asthma, which could relate to data generated by self-reports instead of actual diagnoses.
Some examples of differing benefits: Breast-feeding’s beneficial influence on BMI decreased by 66 percent between siblings across families and siblings within families. The magnitude of the beneficial effects of breast-feeding for math, reading, vocabulary and intelligence declined by between 69 and 29 percent, respectively, when comparing data across families to data from within families.
“Instead of comparing across families we are comparing within families, completely taking into account all of those characteristics – both measured and unmeasured – that differ by family, such as parental education, household income and race/ethnicity,” Colen explained.
These same differences between samples were found in the analysis of the effects of the duration of breastfeeding.
These findings have implications for health policy, she noted.
“If breast-feeding doesn’t have the impact that we think it will have on long-term childhood outcomes, then even though it is very important in the short-term we really need to focus on other things,” she said. “We need to look at school quality, adequate housing and the type of employment parents have when their kids are growing up.
“We need to take a much more careful look at what happens past that first year of life and understand that breast-feeding might be very difficult, even untenable, for certain groups of women. Rather than placing the blame at their feet, let’s be more realistic about what breast-feeding does and doesn’t do.”
Colen co-authored the study with David Ramey, a Ph.D. candidate in sociology at Ohio State.
This work is supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health & Human Development awarded to the Ohio State University Institute for Population Research.
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Contact: Cynthia Colen, (614) 247-8135; .(JavaScript must be enabled to view this email address) (Email is the best way to reach Colen.)
Written by Emily Caldwell, (614) 292-8310; .(JavaScript must be enabled to view this email address)