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Title: Obesity and common mental disorders : examination of the association using alternative longitudinal models in the Whitehall II prospective cohort study
Author: Jokela, M.
ISNI:       0000 0004 2746 8420
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2012
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This thesis examined the bidirectional association between obesity and common mental disorders (CMDs) using alternative longitudinal models. Although previous evidence from different studies suggests that obesity increases the risk of CMDs and CMDs increase the risk of obesity, a more detailed longitudinal analysis is needed in order to better understand the temporal patterns. The participants were from the Whitehall II prospective cohort study with 5 data collection waves between 1985 and 2009 (n=10,265 participants in total contributing 35,880 person-observations over the follow-up), aged 35 to 55 at baseline. Body mass index (BMI) was determined on the basis of height and weight measured in medical examinations, and CMDs were assessed with the self-reported General Health Questionnaire (GHQ). In addition, several covariates (occupational status, sleep duration, bodily pain, alcohol consumption, smoking, physical activity, longstanding illnesses) were included. Associations were examined using multilevel regression. Obesity increased and the level of CMDs decreased with age. The development of both obesity and CMDs were characterized by cumulative developmental patterns, that is, the risk of future obesity (or CMDs) increased progressively with the number of times the person had been obese (or had CMDs) in previous study phases. Standard longitudinal regression models suggested that obesity was prospectively associated with future CMDs, whereas CMDs did not predict future risk of obesity. However, chronic CMDs increased the risk of obesity, so that only individuals with CMDs in several study phases over the follow-up phase had elevated risk of future obesity. Such cumulative pattern was not observed for chronic obesity in predicting future CMDs. Analysis of changes of BMI and CMDs over time indicated that a decrease in BMI was associated with a future decrease in CMDs, and an increase of CMDs was associated with future increase in BMI. An increase in BMI, however, was not associated with future change in CMDs, and a decrease in CMDs was not associated with a decrease in BMI, suggesting that the associations between changes in BMI and CMDs are dependent on the direction of change in the exposure. Except for bodily pain, the covariates had little if any effect on the associations between obesity and CMDs, and only age showed a consistent moderating effect such that the cross-sectional association and the association between CMDs and the future risk of obesity increased in magnitude with age. The results from several alternative longitudinal models suggest that the bidirectional association between obesity and CMDs is likely to represent the effects of multiple mechanisms that exert their influence over different time periods. Standard longitudinal regression models with only two measurement times are not sufficient to capture such complicated temporal patterns.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available