Increasing variability of body mass and health correlates in Swiss conscripts, a possible role of relaxed natural selection?

Abstract

Background and objectives: The body mass index (BMI) is an established anthropometric index for the development of obesity-related conditions. However, little is known about the distribution of BMI within a population, especially about this distribution's temporal change. Here, we analysed changes in the distribution of height, weight and BMI over the past 140 years based on data of Swiss conscripts and tested for correlations between anthropometric data and standard blood parameters.

Methods: Height and weight were measured in 59 504 young Swiss males aged 18-19 years during conscription in 1875-79, 1932-36, 1994 and 2010-12. For 65% of conscripts in 2010-12, results of standard blood analysis were available. We calculated descriptive statistics of the distribution of height, weight and BMI over the four time periods and tested for associations between BMI and metabolic parameters.

Results: Average and median body height, body weight and BMI increased over time. Height did no longer increase between 1994 and 2010-12, while weight and BMI still increased over these two decades. Variability ranges of weight and BMI increased over time, while variation of body height remained constant. Elevated levels of metabolic and inflammatory blood parameters were found at both ends of BMI distribution.

Conclusions and implications: Both overweight and underweight subgroups showed similar changes in inflammation parameters, pointing toward related metabolic deficiencies in both conditions. In addition to environmental influences, our results indicate a potential role of relaxed natural selection on genes affecting metabolism and body composition.

Keywords: body mass variability; inflammatory parameters; metabolic parameters; overweight; relaxed natural selection; underweight.

Figure 1.

Kernel density plots of height, weight and BMI (left), and distributions of differences from the median (right), per years of conscription

Figure 2.

Comparisons of distributions of absolute differences from the median of BMI (left), and log-transformed differences (right). Modern distributions (2010–12) are in colour. In the top row, 1875–79 is compared to modern data, in the middle row, 1932–39 is compared to modern data and in the bottom row, 1994 is compared to modern data

Figure 3.

Coefficient plots of linear regression model with metabolic parameters as a dependent variable and categorized BMI as an independent variable (20.0–22.4 kg/m² as reference category)