A study from the University of Auckland has found that firstborn sisters are significantly more likely to develop weight-related health problems than their younger siblings, with researchers pointing to differences in placental blood supply as a possible explanation.
The research analysed data from 13,400 pairs of sisters and found that older sisters had a 29 percent greater likelihood of being overweight and a 40 percent higher risk of obesity compared to their younger siblings. Beyond weight, the study also identified elevated risks of diabetes and high blood pressure among firstborn females.
Professor Cutfield of the University of Auckland suggested that firstborn children tend to show greater resistance to insulin, which he believes may substantially increase their risk of developing type two diabetes. He indicated that the difference could originate during pregnancy, specifically in the way the placenta supplies blood to a first child compared to subsequent pregnancies.
Even in cases where an older sister does not have visible weight concerns, the study found that younger sisters were generally leaner across the board. The findings also align with earlier research which had reached similar conclusions about firstborn males, who were previously found to be more prone to excess weight than their younger brothers.
Researchers were careful to stress that the study identifies increased probability, not certainty. The goal of the research is to encourage firstborn siblings to be more aware of their health and to take proactive steps toward maintaining a balanced lifestyle. A healthy diet and regular physical activity remain the most effective tools for managing the risks identified.
