The year you were born may impact obesity risk, according to a recent study.

Researchers from Massachusetts General Hospital found that the impact of a variant in the FTO gene that previous research has linked to obesity risk largely depends on birth year, with no correlation between gene variant and obesity in study participants born in earlier years and a far stronger correlation than previously reported for those born in later years.

"Looking at participants in the Framingham Heart Study, 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," James Niels Rosenquist, lead author of the report, said in a statement. "These results -- to our knowledge the first of their kind -- suggest that this and perhaps other correlations between gene variants and physical traits may very significantly depending on when individuals were born, even for those born into the same families."

For the study, researchers analyzed data from participants in the Framingham Offspring Study -- which follows the children of participants in the original study -- gathered between 1971, when participants ranged in age from 27 to 63, and 2008.

Researchers found that the FTO variants the participants had inherited and when they were born revealed that the previously reported association between a specific FTO variant and body mass index (BMI) was seen, on average, only in participants born in later years.

While this study was not able to identify the environmental differences that combine with FTO variant to increase the risk of obesity, the authors note that post-World War II factors such as increased reliance on technology rather than physical labor and the availability of high-calorie processed foods are likely contributors.

While there was no correlation between the obesity-risk variant and BMI for those born before 1942, in participants born after 1942 the correlation was twice as strong as reported in previous studies.

"Our results underscore the importance of interpreting any genetic studies with a grain of salt and leave open the possibility that new genetic risk factors may be seen in the future due to different genetically-driven responses to our ever-changing environment," Rosenquist said.

The findings are detailed in the current issue of PNAS.