Development of the obesity epidemic in Denmark: Cohort, time and age effects among boys born 1930–1975

Abstract

OBJECTIVE: A global epidemic of obesity is developing, but its causes are still unclear. In Denmark, two periods of steep increases in prevalence of obesity have occurred among young men born in the 1940s and 1960 ± 70s. This study investigated the preceding changes in prevalence of obesity and in the entire body mass index (BMI weightaheight 2 ) distribution by birth cohort, calendar time and age among Danish school boys. METHODS: Children attending Copenhagen schools 1937 ± 1983 had annual health examinations, from which we computerized 1 037 468 measurements of height (m) and weight (kg) of 161 314 boys aged 7 ± 13 y. Obesity was de®ned as age-speci®c BMI exceeding the 95.0, the 99.0 and the 99.9 percentile among those born 1930 ± 1934, the latter corresponding to the prevalence of obesity among the young men in these cohorts. The median, standard deviation, skewness, and the 5th, 25th, 75th and 95th percentiles of the age-speci®c BMI were estimated for each birth cohort. RESULTS: The prevalence of obesity, de®ned by the 99.9 percentile, increased at all ages during the same birth years as among the young men, and, accordingly, at earlier calendar years. The prevalence of obesity, de®ned by the 95.0 percentile, showed a distinctly different pattern: a sharp increase, irrespective of age, during the calendar years 1947 ± 1949, and thereafter a stable level until the 1970s, where a further modest increase began. The prevalence de®ned by the 99.0 percentile showed a mixture of the trends in those de®ned by the 99.9 and 95.0 percentiles. The median BMI showed small¯uctuations, parallel at all ages. The standard deviation and right-sided skewness increased until birth year 1950, but were almost stable thereafter. The pattern of changes in the quartiles mostly re¯ected those in the median. CONCLUSIONS: The prevalence of obesity de®ned by the 99.9 or 99.0 percentile has increased in Danish boys born in the 1940s and since the mid 1960s, without corresponding changes in the central part of the BMI distribution. When de®ning obesity by the 95.0 percentile, there was a sharp distinct age-independent increase in the late 1940s. The development of the obesity epidemic is a heterogeneous phenomenon that has involved changes in environmental in¯uences starting at preschool ages and affecting different subsets of the population, either because of selective exposure or particular susceptibility.

Long-term and recent time trends in the prevalence of obesity among Dutch men and women

“…The observation that the skewness of the BMI-distribution shifted to the left has been reported earlier by Thomsen et al, who studied the increase of BMI levels among children, aged 7 -13 y from Copenhagen, Denmark. 19 Because the lower percentiles of the BMI distribution also increased, although slightly, Thomsen et al concluded that some environmental changes are influencing the entire population, but others mainly a subgroup in the population which is especially susceptible for obesity. We deduce from the steeper increase of high percentiles that subjects who already gained weight, for instance those who are overweight, are at high risk to gain even more weight.…”

Risk factors for childhood overweight: shift of the mean body mass index and shift of the upper percentiles: results from a cross-sectional study

“…33 These findings may provide an explanation for the consistently observed trend to more extreme BMI values in children from high-income countries over recent years. [6][7][8][9] If risk factors of overweight affect particularly children with high BMI-SDS (making them even heavier), incremental exposure to those risk factors would primarily result in more extreme values of BMI in the upper part of the distribution. As the explanatory variables considered represent established risk factors, the observed associations are likely to be causative, although the cross-sectional design per se does not allow for addressing causal inference.…”

“…[1][2][3][4][5] In high-income countries, this trend was associated with a shift in upper parts of the body mass index (BMI) distribution rather than with a shift in the BMI distribution in the whole population. [6][7][8][9] If a risk factor particularly affects children with high BMI and the exposure frequency of this risk factor has increased over time within a population, an increase in upper BMI percentiles could be explained. For example, increasing trends over the past decades have been reported for the exposure to high television (TV) viewing and maternal overweight, 10 both of which accounted for stronger associations in heavier children, resulting in a higher proportion of extremely obese children at the upper end of the BMI distribution.…”

Change in body mass index from adolescence to young adulthood and increased carotid intima-media thickness at 28 years of age: The Atherosclerosis Risk in Young Adults study

“…The prevalence of overweight and obesity in children, adolescents and adults has increased dramatically in the last decades in the USA, 1 Finland, 2 Denmark, 3 Great Britain, 4 the Netherlands 5 and Belgium. 6 Reports from developing countries, such as Thailand 7 and China, 8 showed comparable trends.…”