New research being presented at this year's European Congress on Obesity (ECO) in Maastricht, Netherlands (4-7 May), suggests that rates of obesity in Danish adults have trebled over the past 34 years rising from 6% in 1987 to over 18% in 2021.

The study, by Dr Stine Schramm from the University of Southern Denmark in Copenhagen, underscores the need for concerted population-wide action to reverse this trend and the high level of social inequality in obesity.

During the last decades, the prevalence of obesity (BMI 30 kg/m2 or higher) among adults in Denmark has increased dramatically, but whether this increase has been driven by age, period or cohort effects in Denmark is not known.

To find out more, researchers analysed data for 91,684 participants with height and weight measurement recorded in the Danish Health and Morbidity Studies-;representative surveys of the adult population (aged 16 years and older), conducted in 1987, 1994, 2000, 2005, 2010, 2013, 2017 and 2021.

The authors examined how the increase in obesity prevalence was attributed to change in the population's age distribution (age effect), if people born at specific points in time had a higher risk of obesity (cohort effect) or if the increase affected all age groups and birth cohorts over time (period effect).

The analyses found that the prevalence of obesity increased from 6% in 1987 to over 18% in 2021, with a similar pattern in men (19%) and women (18%) and in all age groups. Obesity prevalence increased by age until age 65-74 years, and declined in the oldest age group (75+ years).

In addition, a strong period effect was found with a linear trend, where the risk of obesity increased continually with each recent survey year. Only a minor part (14%) of the increase in obesity prevalence could be explained by changes in the age distribution of the Danish population and no birth cohorts were found to be at higher risk of obesity.

"We know that there are stark inequalities in obesity across Denmark", says Dr Schramm. "Earlier research has shown that the proportion of obesity is almost three times higher in Danish adults with a low level of education (elementary school, 27%) compared to those with the highest education level (undergraduate degree or higher; 10%). There is also increasing evidence that adult health and disease, including BMI trajectories, are founded in early life. But more research is needed to understand how early life exposures such as psychosocial stress play a role in this. The mechanisms behind the rising obesity prevalence is much more than just a matter of diet and physical activity."

Although the authors cannot draw conclusions about cause and effect from the study, they say that their findings support the notion that secular changes over time are important determinants of the trends in obesity.