Birth order a factor for hypertension, diabetes

Firstborn children could be at increased risk for high blood pressure and diabetes compared with their younger siblings, suggests new research from New Zealand.

Investigators studied 85 healthy prepubertal children aged 4 to 11 years, born at 38 to 40 weeks’ gestation and with appropriate birth weight; 32 were firstborns, 53 were later born. Children were assessed for height, weight, fasting lipid and hormonal profiles, and body composition derived from dual-energy x-ray absorptiometry. They also received 24-hour ambulatory blood pressure monitoring and frequent intravenous glucose tests.

Findings showed that the firstborn children were on average 3 cm taller and slimmer overall than the later-born children. However, the firstborns also had 21% lower insulin sensitivity and 5 mm Hg higher daytime systolic and 4 mm Hg higher daytime diastolic blood pressure than the later-born children. Blood lipids were unaffected by birth order.

The researchers suggest that the differences in insulin sensitivity and blood pressure could be because changes in the uterus during a first pregnancy increase the flow of nutrients to fetuses during subsequent pregnancies, placing younger siblings at lower risk for hypertension and diabetes than their firstborn brother or sister.

However they caution that these markers should not be used solely as evidence of lifetime risk. Puberty and lifestyle also can influence insulin sensitivity and affect the risk for hypertension and metabolic and cardiovascular disease later in life.