TUESDAY, July 9, 2019 (HealthDay News) — Environment most likely remains the main contributor to the obesity epidemic in Norway, given that body mass index (BMI) has increased for both genetically predisposed and nonpredisposed people since the 1960s, according to a study published online July 3 in The BMJ.

Maria Brandkvist, from the Norwegian University of Science and Technology in Trondheim, and colleagues used longitudinal data from the Nord-Trøndelag Health Study (118,959 people aged 13 to 80 years) to assess trajectories of BMI in Norway over five decades. Obesity increased in Norway starting between the mid-1980s and mid-1990s. A subset of 67,305 participants was included in analyses assessing genetic predisposition and BMI.

The researchers found that those born after 1970 already had a substantially higher BMI in young adulthood compared with older birth cohorts. For all ages at each decade, BMI differed substantially between the highest and lowest fifths of genetic susceptibility, with the difference increasing gradually from the 1960s to the 2000s. Compared with those who were least genetically predisposed, the most genetically predisposed 35-year-old men had 1.20 kg/m² higher BMI in the 1960s versus 2.09 kg/m² in the 2000s. For women of a similar age and time period, corresponding differences in BMI were 1.77 kg/m² and 2.58 kg/m².

“This study provides evidence that genetically predisposed people are at greater risk for higher BMI and that genetic predisposition interacts with the obesogenic environment resulting in higher BMI, as observed between the mid-1980s and mid-2000s,” the authors write.

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