First born women are more likely to be overweight or obese as adults as compared to their younger sisters, suggests a new research the findings of which have been published in the Journal of Epidemiology & Community Health.
Researchers from New Zealand analyzed data collected from 13,406 pairs of sisters between 1991 and 2009. They carefully noted the women’s height and weight besides other information like family history, current health and lifestyle.
They saw that the first borns were more likely to have a lower birth weight than their younger sisters but had a higher BMI as adults besides being at a greater chance of being overweight or obese.
First born sisters were 29% more likely to be overweight and 40% more likely to be obese as compared to the second born sisters, to be specific. As if it were some consolation, the first borns were also seen to be slightly taller.
“This is the fourth study we have done to characterize the health risks of firstborn in four different populations,” said lead researcher Dr. Wayne Cutfield, a professor of pediatric endocrinology at the Liggins Institute of the University of Auckland in New Zealand.
“If you look at the health risks of those that are firstborn, you find that firstborns are more insulin resistant than later borns, which is a risk factor for diabetes, and they have higher blood pressure than later borns,” he said.
He suggests that the change in the blood supply to the placenta between the first and the subsequent pregnancies due to dilation of blood vessels could be one of the reasons.
Dr. Maria Peña, Director of the Center for Weight Management at Lenox Hill Hospital in New York City, says although this is one plausible theory, environmental factors are most likely also at play.
“In many cultures, moms are more meticulous with their firstborns,” she told CBS News. “With the very firstborn, everyone’s helping out and over-feeding the baby, making sure it’s at a ‘healthy weight.’ But with second children, parents know what to expect and they’re not so overprotective so maybe they feed them a little less.”
She however suggested looking into a broader cross section of population and including women of different races, socioeconomic backgrounds and education levels before jumping to conclusions.