The way the order of birth impacts one's life has always been a matter of research and one of the most mysterious questions to solve. The first-born tend to hold an esteemed place in their lives in terms of social and winning skills. However, a latest research has claimed that they are at a greater risk of obesity than their younger siblings.

Based on the analysis of the data of 13,406 pairs of sisters in Sweden, the researchers found that even though the older sibling weighed less than their younger sister at the time of the birth, the trend reversed as they grew up. In adulthood, the firstborns were found to be more likely to have a significantly greater Body Mass Index, or BMI, than the ones born later, meaning that the firstborns were at a greater risk of being overweight or obese.

The research was conducted collaboratively by a team from the University of Auckland in New Zealand and the Uppsala University in Sweden. The researchers noticed that over a long period of time, such as 18 years, the older sibling accumulated an extra 0.11 kg (0.24 pound) per year, a considerable increase in the BMI.

Overall, the researchers found the older siblings to be at a 29 percent greater risk of being overweight and 40 percent more likely to develop obesity compared to their younger siblings. In addition, the older siblings were found to be marginally taller than their younger sisters by a mere 1.2 millimeters. The complete details of the study have been published in the Journal of Epidemiology & Community Health.

The research team further said that although they were not sure about why the BMI tends to be greater in the firstborns as they grow older, however, the shrinking family size could be one reason.

"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," the team concluded in their study.