Age-period-cohort analysis for trends in body mass index in Ireland.
BACKGROUND
Obesity is a growing problem worldwide and can often result in a variety of negative health outcomes. In this study we aim to apply partial least squares (PLS) methodology to estimate the separate effects of age, period and cohort on the trends in obesity as measured by body mass index (BMI).


METHODS
Using PLS we will obtain gender specific linear effects of age, period and cohort on obesity. We also explore and model nonlinear relationships of BMI with age, period and cohort. We analysed the results from 7,796 men and 10,220 women collected through the SLAN (Surveys of Lifestyle, attitudes and Nutrition) in Ireland in the years 1998, 2002 and 2007.


RESULTS
PLS analysis revealed a positive period effect over the years. Additionally, men born later tended to have lower BMI (-0.026 kg · m(-2) yr(-1), 95% CI: -0.030 to -0.024) and older men had in general higher BMI (0.029 kg · m(-2) yr(-1), 95% CI: 0.026 to 0.033). Similarly for women, those born later had lower BMI (-0.025 kg · m(-2) yr(-1), 95% CI: -0.029 to -0.022) and older women in general had higher BMI (0.029 kg · m(-2) yr(-1), 95% CI: 0.025 to 0.033). Nonlinear analyses revealed that BMI has a substantial curvilinear relationship with age, though less so with birth cohort.


CONCLUSIONS
We notice a generally positive age and period effect but a slightly negative cohort effect. Knowing this, we have a better understanding of the different risk groups which allows for effective public intervention measures to be designed and targeted for these specific population subgroups.
Division of Epidemiology & Biostatistics, School of Medicine, University of Leeds, Room 8,49, Level 8, Worsley Building, Leeds LS2 9JT, UK. mt10tj@leeds.ac.uk.
Tao
T
Jiang
Mark S
MS
Gilthorpe
Frances
F
Shiely
Janas M
JM
Harrington
Ivan J
IJ
Perry
Cecily C
CC
Kelleher
Yu-Kang
YK
Tu
D000328:Adult; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000503:physiopathology