First-born children have greater difficulty absorbing sugars into the body and have higher daytime blood pressure than children who have older siblings, according to the study conducted at the University of Auckland's Liggins Institute in New Zealand. The study was the first to document a 21 percent drop in insulin sensitivity among first-born children.
The good news for them---the study found they tended to be taller and slimmer than their younger brothers and sisters.
Researchers say the metabolic differences in younger siblings might be caused by physical changes in the mother's uterus during her first pregnancy. As a result of the changes, nutrient flow to the fetus tends to increase during subsequent pregnancies.