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Retirement age and the age of onset of Alzheimer's disease: results from the ICTUS study.

Grotz C, Letenneur L, Bonsang E, Amieva H, Meillon C, Quertemont E, Salmon E, Adam S, ICTUS/DSA gro - PLoS ONE (2015)

Bottom Line: Linear mixed models, adjusted for gender, education, occupation, center, country, household income, depression and cardiovascular risk factors were conducted on 815 patients. (1) The global analyses (n = 815) revealed that later age at retirement was associated with later age at diagnosis (β = 0.31, p < 0.0001); (2) once the selection bias was considered (n = 637), results showed that this association was weaker but remained significant (β = 0.15, p = 0.004); (3) once the bias of the reverse causality (i.e., the possibility that subjects may have left the workforce due to prior cognitive impairment) was considered (n = 447), the effect was no longer significant (β = 0.06, p = 0.18).The present study supports that there is an association between retirement age and age at onset of AD.Further prospective investigations are mandatory in order to correctly address this question.

View Article: PubMed Central - PubMed

Affiliation: University of Liège, Psychology of Aging Unit, Liège, Belgium.

ABSTRACT

Objectives: To test whether deferred retirement is associated with delayed onset of Alzheimer's disease (AD), and, if so, to determine whether retirement age still predicts the age at onset of AD when two potential biases are considered.

Methods: The study sample was gathered from the Impact of Cholinergic Treatment Use/Data Sharing Alzheimer cohort (ICTUS/DSA), a European study of 1,380 AD patients. Information regarding retirement age, onset of symptoms and covariates was collected at baseline whereas age at diagnosis was gathered from the patient's medical record prior to study entry. Linear mixed models, adjusted for gender, education, occupation, center, country, household income, depression and cardiovascular risk factors were conducted on 815 patients.

Results: (1) The global analyses (n = 815) revealed that later age at retirement was associated with later age at diagnosis (β = 0.31, p < 0.0001); (2) once the selection bias was considered (n = 637), results showed that this association was weaker but remained significant (β = 0.15, p = 0.004); (3) once the bias of the reverse causality (i.e., the possibility that subjects may have left the workforce due to prior cognitive impairment) was considered (n = 447), the effect was no longer significant (β = 0.06, p = 0.18).

Conclusion: The present study supports that there is an association between retirement age and age at onset of AD. However, the strength of this association appears to be overestimated due to the selection bias. Moreover, the causality issue remains unresolved. Further prospective investigations are mandatory in order to correctly address this question.

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Distribution of the age at diagnosis of Alzheimer’s disease according to age at retirement (N = 815).
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pone.0115056.g002: Distribution of the age at diagnosis of Alzheimer’s disease according to age at retirement (N = 815).

Mentions: Step 1. Fig. 2A displays the age at diagnosis as a function of the age at retirement in the sample of 815 subjects. A positive association was observed between the age at retirement and the age at diagnosis (β = 0.33, p < 0.0001) and a similar association was found for the age at onset of first symptoms (β = 0.30, p < 0.0001). Controlling for potential confounding factors did not change the intensity of the associations: deferred retirement was associated with delayed age at diagnosis (β = 0.31, p < 0.0001) and delayed age at onset of symptoms (β = 0.30, p < 0.0001). In other words, each additional year of employment delayed the age at onset of symptoms by 0.30 years and the age at diagnosis by 0.31 years. Fig. 2B also shows that due to the selection of subjects who developed dementia after retirement, no data are observed in the lower right-hand side of the chart, suggesting that the subjects who retired later in life influence part of the observed association. As mentioned earlier, a patient who retired at 60 years of age could only develop AD after this age whereas a patient who retired at 80 years of age could not develop AD before turning 80. Therefore, the patient who retired later necessarily has a greater probability of being diagnosed at a later age in comparison to the patient who retired sooner.


Retirement age and the age of onset of Alzheimer's disease: results from the ICTUS study.

Grotz C, Letenneur L, Bonsang E, Amieva H, Meillon C, Quertemont E, Salmon E, Adam S, ICTUS/DSA gro - PLoS ONE (2015)

Distribution of the age at diagnosis of Alzheimer’s disease according to age at retirement (N = 815).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340903&req=5

pone.0115056.g002: Distribution of the age at diagnosis of Alzheimer’s disease according to age at retirement (N = 815).
Mentions: Step 1. Fig. 2A displays the age at diagnosis as a function of the age at retirement in the sample of 815 subjects. A positive association was observed between the age at retirement and the age at diagnosis (β = 0.33, p < 0.0001) and a similar association was found for the age at onset of first symptoms (β = 0.30, p < 0.0001). Controlling for potential confounding factors did not change the intensity of the associations: deferred retirement was associated with delayed age at diagnosis (β = 0.31, p < 0.0001) and delayed age at onset of symptoms (β = 0.30, p < 0.0001). In other words, each additional year of employment delayed the age at onset of symptoms by 0.30 years and the age at diagnosis by 0.31 years. Fig. 2B also shows that due to the selection of subjects who developed dementia after retirement, no data are observed in the lower right-hand side of the chart, suggesting that the subjects who retired later in life influence part of the observed association. As mentioned earlier, a patient who retired at 60 years of age could only develop AD after this age whereas a patient who retired at 80 years of age could not develop AD before turning 80. Therefore, the patient who retired later necessarily has a greater probability of being diagnosed at a later age in comparison to the patient who retired sooner.

Bottom Line: Linear mixed models, adjusted for gender, education, occupation, center, country, household income, depression and cardiovascular risk factors were conducted on 815 patients. (1) The global analyses (n = 815) revealed that later age at retirement was associated with later age at diagnosis (β = 0.31, p < 0.0001); (2) once the selection bias was considered (n = 637), results showed that this association was weaker but remained significant (β = 0.15, p = 0.004); (3) once the bias of the reverse causality (i.e., the possibility that subjects may have left the workforce due to prior cognitive impairment) was considered (n = 447), the effect was no longer significant (β = 0.06, p = 0.18).The present study supports that there is an association between retirement age and age at onset of AD.Further prospective investigations are mandatory in order to correctly address this question.

View Article: PubMed Central - PubMed

Affiliation: University of Liège, Psychology of Aging Unit, Liège, Belgium.

ABSTRACT

Objectives: To test whether deferred retirement is associated with delayed onset of Alzheimer's disease (AD), and, if so, to determine whether retirement age still predicts the age at onset of AD when two potential biases are considered.

Methods: The study sample was gathered from the Impact of Cholinergic Treatment Use/Data Sharing Alzheimer cohort (ICTUS/DSA), a European study of 1,380 AD patients. Information regarding retirement age, onset of symptoms and covariates was collected at baseline whereas age at diagnosis was gathered from the patient's medical record prior to study entry. Linear mixed models, adjusted for gender, education, occupation, center, country, household income, depression and cardiovascular risk factors were conducted on 815 patients.

Results: (1) The global analyses (n = 815) revealed that later age at retirement was associated with later age at diagnosis (β = 0.31, p < 0.0001); (2) once the selection bias was considered (n = 637), results showed that this association was weaker but remained significant (β = 0.15, p = 0.004); (3) once the bias of the reverse causality (i.e., the possibility that subjects may have left the workforce due to prior cognitive impairment) was considered (n = 447), the effect was no longer significant (β = 0.06, p = 0.18).

Conclusion: The present study supports that there is an association between retirement age and age at onset of AD. However, the strength of this association appears to be overestimated due to the selection bias. Moreover, the causality issue remains unresolved. Further prospective investigations are mandatory in order to correctly address this question.

Show MeSH
Related in: MedlinePlus