First-born Women Tend To Have More Weight Than Sisters

Birth order of sisters tends to affect their weight. Research has found that first-born women are more likely to be overweight/obese as adults than their second-born sisters.

Research published online in the Journal of Epidemiology & Community Health has published the study, which is the largest of its kind for women, reports dbtechno.com.

"Ours was not only the largest study of birth order effects on women, but was also the only one focusing specifically on sibling pairs, to largely account for genetic factors and the early life environment," wrote Wayne Cutfield, a researcher at the Liggins Institute at the University of Auckland and the lead author of the women's study, according to the Washington Post.

Hence, first-borns were found to be 29 percent more likely to be overweight and 40 percent more likely to be obese than the younger sisters.

The cause of this is probably due to a change in the blood supply to the placenta between the first and later pregnancies. Vessels tend to be narrower the first time, bringing down the nutrient supply to the fetus, says Cutfield. It tends to reprogram the regulation of fat and glucose. When the person becomes an adult, there will be greater storage of fat, with insulin working less effectively, reports CBS News.

"Our study corroborates other large studies on men, as we showed that firstborn women have greater BMI and are more likely to be overweight or obese than their second born sisters," Cutfield writes, concluding that, "the steady reduction in family size may be a contributing factor to the observed increase in adult BMI worldwide, not only among men, but also among women," according to hngn.