Influence of individual and combined healthy behaviours on successful aging

Séverine Sabia; Archana Singh-Manoux; Gareth Hagger-Johnson; Emmanuelle Cambois; Eric J. Brunner; Mika Kivimaki

doi:10.1503/cmaj.121080

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Re:Residual confounding may have constituted a major limitation
Severine Sabia

Published on: 14 December 2012
Residual confounding may have constituted a major limitation
Philipe S Barreto

Published on: 13 December 2012

Published on: (14 December 2012)

Re:Residual confounding may have constituted a major limitation
Severine Sabia
Other Contributors:
We thank Barreto for his considerate comments on our paper.1 In the Whitehall II study, it is indeed possible to take into account a number of covariates that potentially influence the odds of successful aging. The models reported in our paper were adjusted for socio-demographic measures: age, sex, education and marital status. As suggested by Barreto, we undertook new analyses that included further covariates: occupationa...
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We thank Barreto for his considerate comments on our paper.1 In the Whitehall II study, it is indeed possible to take into account a number of covariates that potentially influence the odds of successful aging. The models reported in our paper were adjusted for socio-demographic measures: age, sex, education and marital status. As suggested by Barreto, we undertook new analyses that included further covariates: occupational position (high, intermediate and low both in terms of income and status at work), body mass index (BMI), antidepressant use, and self-rated health at baseline. Table 1 shows that the association between health behaviours and successful aging remains robust to these adjustments. However, it is worth noting that some of these covariates (for example BMI or self-reported health) are not only confounders but likely to be on the causal pathway between health behaviours and successful aging.
Table 1. Association between health behaviours and successful aging
Adjusted Odds Ratio* (95% CI)
Model 1 (M1) 1.33 (1.24, 1.43)
Model 2: M1 + occupational position 1.29 (1.20, 1.39)
Model 3: M1 + body mass index 1.31 (1.22, 1.41)
Model 4: M1 + antidepressant use 1.34 (1.24, 1.44)
Model 5: M1 + self-rated health 1.25 (1.16, 1.35)
Fully adjusted model 1.20 (1.11, 1.30)
*Odds ratio for 1-increment in the healthy behaviour score (the number of healthy behaviours).
M1 is adjusted for age, sex, marital status, and education.
Reference List
(1) Sabia S, Singh-Manoux A, Hagger-Johnson G, Cambois E, Brunner EJ, Kivimaki M. Influence of individual and combined healthy behaviours on successful aging. CMAJ 2012;184:1985-1992.
Conflict of Interest:
None declared
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Competing Interests: None declared.
Published on: (13 December 2012)

Residual confounding may have constituted a major limitation
Philipe S Barreto, Researcher
I read with great interest the work of Sabia et al.1 and the commentary by Wilcox.2 Sabia et al. showed that the accumulation of healthy behaviours reduces the risk of mortality and increases the probability of successful aging linearly. However, the multivariate models presented by the authors were poorly adjusted for confounders (only age, sex, level of education, and marital status were taken into account), which rai...
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I read with great interest the work of Sabia et al.1 and the commentary by Wilcox.2 Sabia et al. showed that the accumulation of healthy behaviours reduces the risk of mortality and increases the probability of successful aging linearly. However, the multivariate models presented by the authors were poorly adjusted for confounders (only age, sex, level of education, and marital status were taken into account), which raises the question of important residual confounding. For example, why did not authors adjust their analyses to subjects' body mass index (BMI), self-rated health, income or medications taken? All these variables were, à priori, available for the phase 3 of the Whitehall II study,3 i.e., the baseline data of Sabia et al.'s study. Since BMI,4 self-rated health5 and socio-economic status,6 and some medications (such as psychotropic drugs)7 are associated to adverse health outcomes, they represent potential confounders that should be controlled for. Therefore, Sabia et al.'s findings must be interpreted with caution since the presence of residual cofounding in their analyses is highly possible; this might have changed their results.
References
1. Sabia S, Singh-Manoux A, Hagger-Johnson G, et al. Influence of individual and combined healthy behaviours on successful aging. CMAJ. 2012; 184(18):1985-1992.
2. Willcox B. Successful aging: Is there hope? CMAJ. 2012; 184(18):1973- 1974.
3. Marmot M, Brunner E. Cohort Profile: the Whitehall II study. Int J Epidemiol. 2005;34(2):251-256.
4. Katzmarzyk PT, Reeder BA, Elliott S, et al. Body mass index and risk of cardiovascular disease, cancer and all-cause mortality. Can J Public Health. 2012;103(2):147-151.
5. Nery Guimarães JM, Chor D, Werneck GL, et al. Association between self -rated health and mortality: 10 years follow-up to the Pró-Saúde cohort study. BMC Public Health. 2012;12:676.
6. Lima-Costa MF, Steptoe A, Cesar CC, et al. The influence of socioeconomic status on the predictive power of self-rated health for 6- year mortality in English and Brazilian older adults: the ELSA and Bambui cohort studies. Ann Epidemiol. 2012;22(9):644-648.
7. Huybrechts KF, Rothman KJ, Silliman RA, et al. Risk of death and hospital admission for major medical events after initiation of psychotropic medications in older adults admitted to nursing homes. CMAJ. 2011;183(7):E411-419
Conflict of Interest:
None declared
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Competing Interests: None declared.