After decades of being made to believe that breastfeeding is best, a new study has shown that that might not be true after all.

A new study analyzed data gathered from 8,237 children, 7,319 siblings and 1,773 sibling pair where at least one of the siblings was breast-fed and the other sibling was not. This data was from the National Longitudinal Survey of Youth (NLSY), specifically their data from the surveys of 1979 cohort that covered young and women aged between 14 and 22, and results from surveys gathered between 1986 and 2010 of children born to women in the 1979 cohort.

The information was then measured for body mass index (BMI), obesity, asthma, hyperactivity, parental attachment, behavioral compliance, and cognitive achievements, such as in vocabulary, reading, math, and intelligence, and scholastic competence. These 11 outcomes have been previously shown to be affected by breast-feeding.

When the researchers looked at the data gathered across all the families, they found that those children who have been breast-fed fared better than the bottle-fed children when it came to BMI, hyperactivity, math skills, reading recognition, vocabulary word identification, digit recollection, scholastic competence, and obesity.

However, when the researchers looked only at the group composed of pairs of siblings, in which one was breast-fed and the other was bottle-fed, they saw that there was not much difference between the performance of the siblings on the outcomes measured. The only difference that the researchers have noticed is that the breast-fed siblings were at a higher risk for asthma.

It appears that there was no clear long-term health difference between those who were breast-fed and those who were bottle-fed. These findings, published in the journal Social Science & Medicine, call attention to the possibility that what we have been taught to believe about breast-feeding may be overhyped, as many health and brain conditions attributed to breastfeeding may actually have been caused by other factors.

"Many previous studies suffer from selection bias. They either do not or cannot statistically control for factors such as race, age, family income, mother's employment - things we know that can affect both breast-feeding and health outcomes," said Cynthia Colen, assistant professor of sociology at The Ohio State University and lead author of the study. "Moms with more resources, with higher levels of education and higher levels of income, and more flexibility in their daily schedules are more likely to breast-feed their children and do so for longer periods of time."

This new study has repercussions that go beyond the household. It just may influence future health policies, since it is apparent that, because breast-feeding has now been proven to be not the only factor affecting the physical and mental health of children.

"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," Colen 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," she further explained.