Older sisters often grumble that their siblings born later than them are blessed with all the luck. But it looks like they actually do have something to complain about – as research has revealed that younger sisters are more likely to be slimmer than firstborn girls.
The findings of the study indicate that birth order may play a key role in determining weight.
Furthermore, researchers warned that firstborns are at risk of other health problems as well.
The scientists after analyzing data on the health of 13,400 pairs of sisters concluded that firstborn women were, on average, 29 per cent more likely to be overweight and 40 per cent more likely to be obese than second-born sisters.
The findings corroborates similar research on men that inferred firstborn males were more likely to be overweight than younger brothers.
The latest research analyzed data from pregnant Swedish women, collected between 1991 and 2009. Weighed when they were between ten and 12 weeks pregnant, firstborn women were 1lb 4oz heavier on average than second-born sisters.
Their body mass index (BMI) was calculated as 2.4 per cent higher. Firstborn sisters were just slightly taller, measuring an additional 1.2mm on average.
Asides from that researchers noted a significant increase in average weight over the 18-year period, rising by four ounces per year.
The experts, from the University of Auckland in New Zealand and Uppsala University in Sweden, stated they were unclear about why older sisters seemed to be heavier. However, they opined the findings could throw light on why obesity figures appear to be soaring.
As families are shrinking, with majority of parents reluctant to have more than two children, a greater percentage of people today are firstborns than in the past. Thus, if firstborns are more likely to be overweight, that will raise obesity rates.
Firstborn are more likely to be overweight, according to a study
The scientists furthermore said there is a clear indication that firstborns are more at risk of health problems like diabetes and high blood pressure in later life than their siblings. But the root causes for these differences are unclear, they added.
Writing in the Journal of Epidemiology and Community Health, the team said: ‘Our study corroborates other large studies on men, as we showed firstborn women have greater BMI and are more likely to be overweight or obese than their second-born sisters.
‘The steady reduction in family size may be a contributing factor to the observed increase in adult BMI worldwide, not only among men, but also among women.’
Furthermore, the researchers noted a significant increase in average weight over the 18-year period, rising by four ounces per year