First she usurps your throne as the reigning princess of the house, then she steals your hair rollers, now you find out your sister may be the reason your baby weight is still lingering even though your "baby" is ten. How can that be?
In a new study published by the Journal of Epidemiology and Community Health, Swedish scientists studied the BMI of over 13,000 pairs of sisters over the course of 20 years from 1991-2009. The purpose was to see if scientists would discover corroborating results from a previously conducted study on brothers. And they did.
Scientists discovered that first-born sisters, the ones who broke in Mom and Dad, are more likely to be smaller as babies but would become heavier and taller than their younger, weaker sisters as adults. Specifically, the elder is about 30% more likely to be overweight than the little runt. Older sisters have an average 2.4% higher BMI than the second born. Moreover, the wiser sibling is 40% more likely to be obese.
Along with the extra weight comes secondary health issues that plague the older sister such as diabetes and high blood pressure. So while the younger sister is merrily enjoying lunch and cocktails with girlfriends, the firstborn is hanging out with Richard Simmons and sweating to the oldies eating only dry grilled chicken.
So how does this happen? Scientists aren't too sure. According to Dr. Wayne Cutfield of Auckland University, in the first pregnancies, the blood vessels that feed the placenta tend to be narrower than later pregnancies which can affect the way glucose is stored in the growing fetuses. CBS News reported that some scientists suggest it could be completely nurture based because, perhaps, older sisters are fed more by excited parents who want to hold their babies constantly. The results could also be attributed to smaller family sizes which don't have multiple births providing sufficient diagnostic comparisons.
The study is completely observational without physical data to understand the specifics. Even though there is a tendency for older siblings to be heavier, your birth order does not predetermine your fate!