What does birth order have to do with an individuals' weight? A new study has revealed that firstborn women are likelier to be overweight or obese as adults than second-born sisters.
The researchers wanted to find out if birth order affected adult women's height and weight as it appears to among adult men. The study found that at birth, firstborns were very slightly lighter than their second born sisters, but as adults during their first three months of pregnancy, their BMI was marginally higher than that of their second born sisters. They were also 29% more likely to be overweight and 40% more likely to be obese than their second born sisters; and they were marginally taller.
The researchers suggested that firstborns might be more at risk of health problems, such as diabetes and high blood pressure, in later life than their siblings, although the potential underlying triggers for these differences were far from clear. They said, "Our study corroborates other large studies on men, as they showed that firstborn women have greater BMI and were more likely to be overweight or obese than their second born sisters."
The researchers concluded that the steady reduction in family size might be a contributing factor to the observed increase in adult BMI worldwide, not only among men, but also among women.
The study appeared in the Journal of Epidemiology and Community Health.