Older siblings tend to be overweight or obese

First-borns at increased risk for overweight and obesity
Birth order plays an important role in later body weight, according to recent research by researchers from the University of Auckland in New Zealand and the Swedish University of Uppsala. Previous studies have already shown that first-borns tend to grow larger and weigh more than later-born siblings. Now the scientists have clearly shown that in women, the first-born tend to be much more likely to overweight than their younger sisters.

First-born women are 29 percent more likely to be overweight and 40 percent more likely to be obese than their younger siblings later in life, scientists around José Derraik of the University of Auckland report in the journal Journal of Epidemiology and Community Health ". The correlation between body weight and birth order could, according to the researchers, also be a reason for the increased prevalence of obesity in modern industrialized nations. Continuous family downsizing may be a determining factor in the observed increase in adult body mass index (BMI), the researchers conclude.

First-borns have weight problems significantly more often than their younger siblings. (Image: BillionPhotos.com/fotolia.com)

Risk of overweight increased by 29 percent
In their current study, the researchers evaluated the data from 13,406 sister couples (26,812 women) from the Swedish birth registry, which also included information on the weight, height, lifestyle and family history of the subjects. The scientists found that the first-born women already had a slightly higher BMI during pregnancy (+2.4 percent) than their second-born sisters. In addition, the likelihood of later overweight in the first-born was 29 percent higher. In adiposity, the risk of the first-born was according to the researchers even increased in 40 percent. Significant differences in size, however, were not found. The older sisters were on average only 1.2 millimeters larger.

Small families reason for the prevalence of obesity?
For the first-born, the current study results mean that they have to pay more attention to their body weight than their younger siblings, so as not to become overweight. However, scientists at the University of Auckland and Uppsala University also see their findings as a possible explanation for the increasing prevalence of overweight and obesity worldwide. The small families, with only one child, may play a significant role in the observed increase in adult BMI, explain Derraik and colleagues. (Fp)