First born children may have a higher risk of diabetes, according to the Endocrine Society.
"Although birth order alone is not a predictor of metabolic or cardiovascular disease, being the first-born child in a family can contribute to a person's overall risk," said Dr. Wayne Cutfield of the University of Auckland in New Zealand.
A new study from the university's Liggins Institute found that the oldest children in a family tend to have higher daytime blood pressure and have more trouble digesting sugars. The study, published in The Endocrine Society's Journal of Clinical Endocrinology and Metabolism, found a 21 percent drop in insulin sensitivity in first-born children.
The study focused on 85 children ages four to 11. Adults and teenagers were left out of the study because insulin levels can be affected by puberty and adult lifestyles. In addition to the reduction in insulin sensitivity, the first-born children also showed a four mmHg increase in blood pressure.
The lower insulin sensitivity and increased blood pressure could be caused by changes that occur in a first-time mother's uterus during pregnancy. These changes increase nutrient flow during later pregnancies, but don't affect first-born children. First-born and only children also tend to be taller and slimmer than their siblings. These results remained even after adjusting for the body mass index and height of their parents.
These results have major implications to the changing family dynamic around the world. As family size decreases, an increasing proportion of the world population is now made up of first-born children. In a country like China, where a one-child policy is in place for urban families, the number of one child families (and first-born children) is much higher. This could mean much higher numbers of health ailments connected to lower insulin sensitivity and higher blood pressure, like Type II diabetes, stroke, hypertension and coronary artery disease.
"Our results indicate first-born children have these risk factors, but more research is needed to determine how that translates into adult cases of diabetes, hypertension and other conditions," said Dr. Cutfield.