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. 2013 Jun;42(3):828-37.
doi: 10.1093/ije/dyt052. Epub 2013 Jun 14.

Age, period and cohort effects on adult body mass index and overweight from 1991 to 2009 in China: the China Health and Nutrition Survey

Lindsay M Jaacks  1 , Penny Gordon-Larsen, Elizabeth J Mayer-Davis, Linda S Adair, Barry Popkin
Affiliations

Age, period and cohort effects on adult body mass index and overweight from 1991 to 2009 in China: the China Health and Nutrition Survey

Lindsay M Jaacks et al. Int J Epidemiol. 2013 Jun.

Abstract

Background: Contributions of age-period-cohort effects to increases in BMI and overweight among Chinese adults must be resolved in order to design appropriate interventions. The objectives were to (i) describe the period effect on BMI and overweight among Chinese adults from 1991 to 2009 and assess modification of this effect by age (e.g. cohort effect) and gender, and (ii) quantify the influence of household income and community urbanicity on these effects.

Methods: Data are from the China Health and Nutrition Survey, a prospective sample across nine provinces in China; 53,298 observations from 18,059 participants were collected over a 19-year period. A series of mixed effects models was used to explicitly assess differences in BMI within individuals over time (age effect) and population-wide differences in BMI over time (period effect), and implicitly assess differences in the experienced period effect across individuals of varying ages (cohort effect).

Results: Stronger period effects on BMI and overweight were observed among males compared with females; and younger cohorts had higher BMIs compared with older cohorts. Simulations predicted that increases in income and urbanicity in the order of magnitude of that observed from 1991 to 2009 would correspond to shifts in the BMIs of average individuals of 0.07 and 0.23 kg/m(2), respectively.

Conclusions: Although period effects had a stronger influence on the BMI of males, interventions should not overlook younger female cohorts who are at increased risk compared with their older counterparts.

Keywords: Age-period-cohort analysis; China; body mass index; overweight.

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Figures

Figure 1
Figure 1
Predicted BMI (kg/m2) from final adjusted linear mixed effects model (Series A, Model 3) for an average 25- and 45-year-old male and female in 1991 compared with 2009 at mean values for covariates (household income, community urbanicity and Mill’s ratio) over all survey years. The change in BMI from 1991 to 2009 was greatest for the older male (1.50 kg/m2) and lowest for the younger female (0.23 kg/m2)
Figure 2
Figure 2
Response profiles of 1269 participants with measurements for all 7 surveys stratified by baseline age group (cohort) among (a) males and (b) females. Points represent mean BMI (kg/m2) at mean age (years) for each cohort across survey years (1991, 1993, 1997, 2000, 2004, 2006 and 2009). The difference between lines represents differences in the experienced period effect by baseline age group, equivalent to a cohort effect
Figure 3
Figure 3
Secular trends in BMI (kg/m2) for 1269 participants with measurements for all 7 surveys among (a) males and (b) females. Bars represent differences from referent BMI (1991), estimated by unadjusted linear mixed effects models stratified by baseline age group (cohort). Results indicate that the period effect was strongest for younger baseline age groups
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