How does the body mass index (BMI) develop over the course of life? What trends are there from generation to generation? And how do ethnicity, education and social class influence body weight? A US study answers these questions using longitudinal data for cohorts since the 1890s. Accordingly, the average BMI of each generation was higher than that of the previous one. In addition, the body weight of those born later increases with increasing speed at a young age. The problems are particularly serious among blacks and Hispanics, as well as those with a low level of education.
Overweight, obesity and the associated health risks are a problem for more and more people in industrialized nations. In the US, more than 70 percent of all adults in 2016 had a body mass index over 25 and were therefore considered overweight. From an epidemiological point of view, the increasing proportion of overweight children and adolescents is a particular cause for concern, because those who are too fat at a young age often have difficulties in achieving a healthy weight as adults. How exactly the BMI develops over the course of life and which trends can be observed over generations have not yet been systematically recorded.
BMI grows stronger and faster
A team led by Yang Claire Yang from the University of North Carolina has now evaluated four large US longitudinal studies based on this information. In doing so, they were able to fall back on the data of almost 65,000 respondents between 11 and 107 years of age. They divided these into five-year cohorts according to their birth cohort and analyzed the BMI for each birth cohort individually. In addition, they evaluated the ethnicity, educational level and educational level of the parents for all respondents and related these influencing factors to the BMI.
“In younger birth cohorts, the BMI was higher on average and increased faster than in cohorts born earlier,” the researchers report. While people born between 1950 and 1954 had an average BMI of 25.8 at the age of 30, which corresponds to slightly overweight, the BMI for people born between 1980 and 1984 at the same age was 30.2, so in the area of obesity. Across the birth cohorts, the researchers observed the trend that BMI increases from adolescence to adulthood, with the increase being steeper in younger cohorts. After a maximum of between 50 and 69 years, body weight decreases again from the age of 70, for example as a result of illnesses.
Education and ethnicity as influencing factors
Yang and colleagues identified the parents’ level of education and their own educational qualifications as important influencing factors. “Higher educational qualifications of parents and respondents were associated with lower BMI values in all age groups,” they write. “For women whose parents had a university degree, the increase in the mean BMI over the course of life was also lower.”
According to the analysis, ethnicity also played a role: “Compared to whites, blacks and Hispanics had significantly higher BMI values earlier in life, which persisted in all age groups,” said the researchers. The differences are only partly due to the different socio-economic status. “A possible mechanism for this inequality in the BMI course is that the burden of discrimination and the different access to health resources lead to the fact that biological aging processes accelerate or that the minorities display less health-promoting behaviors compared to whites”, explain the Authors. The stress of everyday discrimination alone could have a negative impact on weight and health.
The influence of both ethnic and educational differences was more pronounced in younger cohorts. The researchers see a worrying trend here, but there are also possibilities to counteract this. “This study identifies adolescence and young adulthood as a critical time window in which obesity can grow rapidly and in which racial and educational inequalities arise that solidify in adulthood,” they write. That is why it is particularly important to start with prevention programs here.
Source: Yang Claire Yang (University of North Carolina at Chapel Hill, USA) et al., Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2020167118