One thing that no one thought would ever influence obesity is reportedly quite important: your birth year.

A new study reportedly shows that a gene that’s been shown to strongly influence obesity can actually make people fatter, but only if they were born after 1942, according to NBC News.

A study done by researchers from Harvard Medical School reportedly found that people born before 1942 were less likely to be affected by a gene variant linked to obesity than those born after that year, according to NewsEveryDay.

“We found that the correlation between the best known obesity-associated gene variant and body mass index increased significantly as the year of birth of participants increased,” stated lead author James Niels Rosenquist from Massachusetts General Hospital, in a press release.

About 20 percent of white people reportedly have a variant of the gene, which is called FTO. According to a study done back in 2007, British scientists reportedly found that people who carry two copies of this variation of the FTO gene weighed, on average, seven pounds more than people who lack it.

For the recent study, the Framingham Heart Study, an ongoing study of more than 10,000 people who fill out questionnaires and get medical exams every few years, was reportedly used. Those who had a version of the FTO gene reportedly gained weight as he or she got older.

“What we wanted to see was whether there was a difference for people born in the earlier part of the cohort, during the 1920s, [when compared to] to people born in the later part of the cohort, in the 1940s and 1950s,” stated Dr. Rosenquist.

He added, “People born in the early 1940s or before had no increased risk for higher body mass index or obesity. These results— to our knowledge the first of their kind — suggest that this and perhaps other correlations between gene variants and physical traits may vary significantly depending on when individuals were born, even for those born into the same families."