Genetics do matter, but a study has uncovered that birth order might also have an effect, and older sisters have higher chances of being overweight than their younger siblings.
The research was aimed to complete a similar research conducted on men, where it was observed that firstborn males have higher chances of gaining more weight throughout their life than their little brothers. The same principle seems to be available for women.
Researchers gathered data from the Swedish Birth Register of women born between 1991 and 2009 in what is the biggest study of its kind known to date. Similar, but smaller observations have been made in Italy or Poland, to investigate the same curious issues about birth order.
Among the over 206,000 Swedish women born with a sibling within the last 18 years, researchers gathered the data from over 13,400 pairs of sisters, who had a complete chart of information available regarding family history, height, weight, age, and other relevant factors.
It was observed that older sisters had 29% higher chances of becoming overweight throughout their live, and an even bigger 40% chance of qualifying for obesity, in spite of being generally lighter upon birth. Researchers were interested to examine the environmental factors and possible genetic differences between children of the same sex, but of different age in the same family. Twins were not taken into consideration.
Firstborn sisters also are naturally slightly taller by an average of 1.2 millimeters, but also have higher chances of developing conditions like diabetes and high blood pressure. The study has been categorized as ‘observational’, however, so there was no cause-and-effect blamed for the difference in health and weight among sisters.
Theories have been made though, one of which being that the older sibling has much less competition for the resources and the family in general is constantly helped on keeping the child at a ‘healthy weight’. The habit and over protectiveness might lead to overfeeding, which could still affect their lives as adults by instilling more generous meals.
By the time the next sibling appears, parents are commonly more relaxed and have an extensive, first person experience on what is necessary to ensure their child’s health.
Professor Wayne Cutfield, who is lead author of the study, theorized that the problem might also be biological, and that the blood supply to the placenta differs between the first pregnancy and the second. It would narrow the blood vessels and reduce the nutrients, which could cause a reprogramming of the child’s fat and glucose regulation.
However, the possibility has not yet been proven, and has remained at the rank of theory. But the results of the study still stand that firsborns have higher chances of becoming overweight or even obese, whether male or female.
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