New research indicates a fatter future
9 January 2009
Health gains in post-war generations have been overshadowed by increasing obesity, a new study shows.
The research, funded by the Medical Research Council, looked at the differences in height and body mass index (BMI) between generations, using cohorts (generational groups) born in 1946 and 1958. High BMI and excessive BMI gain at different life stages are associated with cardiovascular disease, diabetes, and some cancers, so finding how child-to-adult development of BMI has changed across recent generations may help to identify and control risk in the future.
Although childhood BMI or prevalence of childhood obesity did not increase between the two generations, the 1958 cohort gained weight at a faster rate from early adulthood and continued to do so throughout adult life. This divergence of BMI trajectories in early adulthood coincides with the 1980s obesity epidemic which had an impact on the 1958 group at a younger age.
The graph below shows estimated BMI trajectories and observed mean BMI at different ages for men in the 1946 and 1958 British cohorts. It shows that BMI increased with age more in the 1958 group that the 1946 generation. The findings were echoed in the female cohorts.
In the 1958 cohort, the higher prevalence of adult obesity and excessive weight gain may not necessarily lead to an increase in the incidence of diseases associated with higher BMI; this is because they were also found to be taller and have longer legs, indicating improvements in the early life environment, which would tend to lessen the risks of cardiovascular disease, although not of cancer. At population level, a 1cm increase in height is related to a 4% decrease in cardiovascular disease risk, while a 1cm increase in waist circumference is associated with an increased risk of 2%. So the effect of a 2cm increase in waist may offset a 1cm increase in height.
Dr Leah Li, lead researcher on the project and is funded by a Medical Research Council Career Development Award in Biostatistics, explained:
“Using the results of our study, we can estimate that the average BMI of those born in 1958 will reach 30 kg/m2 for men and 29 kg/m2 for women by age 53 years, and thus the average male population will be obese. With the relatively low level of childhood obesity in these two early cohorts compared with today’s children, if the obesity epidemic continues at its current pace, the level of obesity will increase substantially in the future adult population.”
Notes
This was the first study to compare BMI and height growth in large national cohorts, from birth throughout childhood, adolescence, and across adult life.
BMI is calculated using weight (kg) / height2 (m)
Researchers looked at data on large numbers of people of the same age (birth cohorts) born in 1946 and 1958. Individuals born in 1958 were no heavier at birth than those born in 1946, but they were taller in childhood by about 1cm on average, and then grew faster, achieving adult height earlier at 1cm taller than those born earlier. The height difference was entirely due to a longer leg length in the younger cohort. Leg length has been found to be the component of height most sensitive to early environment. The younger cohort were significantly heavier in adulthood, by 7.1kg (males) and 4.8 kg (females) at 43-45 years.
Components of physical development – in this case growth markers and changes in BMI – are associated with particular adult chronic diseases:
• Low birth weight and short leg length with cardiovascular disease;
• Short stature, short leg length and impaired postnatal growth with diabetes;
• Tall stature with breast cancer.
Original research paper: Child-to-Adult Body Mass Index and Height Trajectories: A Comparison of 2 British Birth Cohorts by Leah Li, Rebecca Hardy, Diana Kuh, Rossella Lo Conte, and Chris Power was published in the American Journal of Epidemiology 2008;168:1008-1015.
The authors are based at the Medical Research Council Centre of Epidemiology for Child Health/Centre for Paediatric Epidemiology and Biostatistics at UCL Institute of Child Health, London, and the MRC unit for Lifelong health and Ageing, Royal Free and UCL Medical School, London.
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