As if you don't have enough to argue about with your siblings, now you can add weight loss to the list. In a study published in the Journal of Epidemiology & Community Health, researchers from New Zealand and Sweden demonstrated that older sisters are at a disadvantage when it comes to weight gain in the largest study ever completed on women's weight gain. After tracking 20 years of medical records for 13,000 pairs of Swedish sisters who were either first born or second born, researchers were able to show that firstborn women are 29 percent more likely to be overweight, and 40 percent more likely to be obese, than their younger sisters.
The research also showed that the differences began at birth. As newborns, firstborn girls were slightly lighter than their second-born sisters. Even as adults, the trend continues with first-born women who were expecting themselves showing a 2.4 percent higher body mass index (BMI) during the first three months of pregnancy than their second-born sisters. Unfortunately, the news doesn't stop there. According to the study, previous research has found that firstborns have a higher risk of diseases like diabetes and high blood pressure.
Men shouldn't get cocky either. The findings from this study are in line with similar ones done on men which show that first-born men are also at an increased risk of diabetes and high blood pressure from their younger siblings.
There is no determined reason.
Researchers from this study acknowledge that it is an observational study and therefore there is no way to draw definitive conclusions as to why this occurs. CBS News reports that some scientists argue that it is caused by variations in nutrition levels in the uterus or placenta, the organs that reprogram how fat and glucose are stored in the body.
Others have hypothesized that it's more environmental factors that are at work. With parents monumentally more nervous about their children they become overprotective which can manifest in parents overfeeding their children to ensure that it's a "healthy weight." This habit can then reprogram children to override their full stomach signals early on in life and lead to later overeating.
Either way, if you're the first-born sister, it appears that there isn't much that you can do about your weight. So you may as well indulge during the holidays!