Obesity Linked To Birth Order: Firstborn Girls More Likely To Be Obese, Overweight

A new study suggests that birth order plays a significant role in determining one's weight as firstborn girls are likely to be obese or overweight when they reach adulthood compared to their younger sisters.

According to ScienceDaily, the researchers wanted to find out if birth order influences adult women's height and weight as in the case of adult men. So they drew data from the Swedish Birth Register starting from 1973. The records contain information dating back to the first antenatal visit on nearly all births in Sweden.

The study concentrates on the years between 1991 to 2009 for women who were at least 18 years old at the time of their first pregnancy and who had been born to a mother who was also 18 years old at the time. The researchers measured their weight and height. They also collected information about health, lifestyle, and family history at the first antenatal visit. Twins were excluded.

The records showed of the 303,301 girls that were born between the years 1973 and 1988, who gave birth between 1991 and 2009, 206,501 were first or second born. Complete data were only available for 13,406 sister pairs.

The records showed that at birth, firstborns were slightly lighter, but as adults, during their first trimester of pregnancy, their BMI was marginally higher at about 2.4 percent. Firstborns were 29 percent more likely to be overweight and had a 40 percent chance to be obese compared to second born sisters.

Lead researcher, Dr. Wayne Cutfield, a professor of  pediatric endocrinology at the Liggins Insititute of the University of Auckland in New Zealand, revealed that this is the fourth study they did that characterized the health risks of firstborns in four different occupations. She stressed that firstborns were more insulin resistant, which was a risk factor for diabetes. They also had higher blood pressure, U.S. News reports.

This study can inspire firstborns to make healthy decisions in their lifestyle. Cutfield said, "I don't want firstborns to think they will become obese or get diabetes or high blood pressure -- it is a risk factor, and the risk of getting a disease is a combination of risk factors, not just a single risk factor."

"This study establishes an association in females, already seen in males, between the likelihood of obesity in adulthood and place in the birth order, but by design, it cannot say for sure why such an association exists," said Dr. David Katz, president of the American College of Lifestyle Medicine.

He suggested thaT firstborns were less well-nourished in the womb or excessively nourished during childhood, or, maybe, there could be life stresses unique to them that could contribute to their condition.

The results of the study was published in the Journal of Epidemiology & Community Health on Wednesday, Aug. 26.