Are You an Older Or Younger Sister? It Can Affect your Weight

If you needed more proof that we’re slaves to the lottery of biology then look no further than a new study put out by the Journal of Epidemiology & Community Health.

The study immediately launches into the bad news (or the good news, depending on where you place in the family).

Firstborn women more likely to be overweight/obese as adults than second-born sisters.

“The findings back up similar research on the impact of male birth order, and prompt the researchers to ponder whether shrinking family size might not be contributing to the observed rise in adult body mass index (BMI) around the globe.”

“At birth, firstborns were very slightly lighter than their second born sisters, but as adults during their first three months of pregnancy, their BMI was marginally higher (2.4%) than that of their second born sisters. They were also 29% more likely to be overweight and 40% more likely to be obese than their second born sisters. And they were marginally taller (1.2 mm).”

“Having more siblings was associated with shorter height and lower odds of being tall, possibly attributable to the ‘resource dilution hypothesis’ which holds that there’s less to go around as a family grows in size”

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This was an observational study however, so this isn’t done and dusted, however it does match up with similiar studies done on men.

For instance it may be hasty to start drawing parallels with the Chinese One Child Policy with rising obesity rates in the country.

Fun thought experiment though.

For the full methodology read the study brief here.