Birth order might affect a person's physical size, with firstborn children being more likely to be taller and thinner than their younger siblings. A 2012 study — which can identify trends but cannot prove the causes — looked at 32 firstborn children younger than 12 years old. It found that although the firstborn children tended to be taller and thinner, they also might be more likely to have higher blood pressure and lowered insulin sensitivity. These conditions might serve as risk factors for developing cardiovascular diseases and diabetes as adults. Researchers believe these differences from birth order could be the result of the uterus getting more nutrients after a first pregnancy because of improved placenta function.
More about birth order:
- About 60% of all people in the world are firstborn children.
- Studies have found that people tend to be more likely to associate with other people who have the same birth order. For example, a firstborn child is more likely to be friends with other firstborns — and someone who is an only child is more likely to associate with other only children.
- Although there might be a slight increase in the risk of cardiovascular diseases and diabetes among firstborn children, other risk factors that might be more important are diet, exercise and stress levels.