Thursday May 21 2009
It is not proven that retiring later delays the onset of dementia
“Working beyond normal retirement age might help stave off dementia”, reported The Guardian. It said that a study of 382 men with probable dementia found that the chances of early onset of Alzheimer's disease could be reduced by keeping the brain active later in life. It quoted one of the researchers as saying, "the intellectual stimulation that older people gain from the workplace may prevent a decline in mental abilities, thus keeping people above the threshold for dementia for longer”.
Unfortunately, the study has several limitations, which mean that it is not possible to conclude on the strength of this study alone that retiring later in life or staying mentally active delays the onset of dementia. Although it is appealing to think that mental stimulation delays the onset of dementia, the evidence so far is not conclusive. Healthy lifestyle choices regarding diet, nutrition, exercise, and intellectual and social activity deserve to be encouraged as they are helpful for a number of reasons. Further research is needed on this subject, preferably also including women and following people from before retirement onwards.
Where did the story come from?
The research was carried out by Michelle Lupton and colleagues from the Institute of Psychiatry at King’s College London and other universities in the UK. The study was funded by a Medical Research Council (MRC) studentship and grants from the Alzheimer’s Research Trust, the MRC and the National Institute for Health Research (NIHR), among other sources. The study was published in the International Journal of Geriatric Psychiatry, a peer-reviewed medical journal.
What kind of scientific study was this?
This cross-sectional study investigated the effects of education, employment and retirement age on the age of onset of Alzheimer’s disease.
The researchers say that previous research has shown that education can protect against developing Alzheimer’s. However, few studies have looked at whether dementia can be delayed by factors such as an individual’s duration of education or their responsibility at work.
The researchers used data from a previous genetics study to obtain data on 1,320 people with probable Alzheimer’s. They were only interested in individuals with employment history and retirement age data, and so only included the 382 men for whom this information was available. Statistical techniques were used to analyse the data for links between these two factors and onset of Alzheimer’s disease.
The previous study identified suitable volunteers through their contact with clinical services, dementia support groups, advertising and residential and nursing homes. The researchers collected data about volunteers’ age at Alzheimer’s onset and past education by questioning friends and relatives.
Diagnosis of probable Alzheimer’s was made using recognised diagnostic criteria from the National Institute of Neurological and Communication Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Associations (NINCDS-ADRDA).
Although there were some details of past employment available for the 382 men, these data were not complete. Those individuals with some missing data (one or two variables missing, 8.1%) and those with much missing data (three or more, 24.1%) were assessed and found not to have a significantly different age of onset to those with no data missing. The researchers simulated the missing data using a technique called imputation, which substitutes the best predicted estimate for the missing value.
The employment data examined included whether the individual was a foreman or manager, how many people were employed at their workplace, how many employees they were responsible for and whether they were self employed.
What were the results of the study?
The researchers say there was no relationship between the age of onset of Alzheimer’s and the number of years of education, highest qualification obtained or other employment data.
They report that later retirement age had a significant effect in delaying the age of onset of Alzheimer’s disease. On average, every extra year of employment delayed the age of onset of Alzheimer’s disease by 0.13 years.
What interpretations did the researchers draw from these results?
The researchers conclude that no effect of education or employment was seen. They offer some explanations for how delaying retirement may be beneficial, suggesting active employment later in life allows an individual to keep their mental processing (cognitive) assets above the threshold for dementia.
What does the NHS Knowledge Service make of this study?
The authors acknowledge several limitations of their study and say that the group of subjects was not ideally suited to “epidemiological enquiry”. These limitations include:
- The original study that supplied the subject data was designed to investigate genes that might increase an individual’s susceptibility to Alzheimer’s Disease. The participants were obtained through referral, meaning that the group could be biased towards people who were more educated or who had an earlier than usual onset of Alzheimer’s disease.
- The volunteers were born between about 1900 and 1940. Educational opportunities may have improved for volunteers who were born in later years. It is possible that any association found might be due to an unknown factor related to age rather than education alone.
- There was a substantial amount of missing data for which values had to be imputed. This may have affected the results of the study.
- This study only included people with probable Alzheimer’s disease, therefore, it cannot say how education or work might affect the risk of developing Alzheimer’s. It can only show how these factors might affect the age of onset of Alzheimer’s in people who are going to develop the disease anyway.
- The biggest limitation to this study is that people who have the early symptoms of dementia, or who have risk factors for dementia, are more likely to retire early than those who have not yet developed these symptoms or risk factors.
Ideally, what is needed now is a large, longitudinal non-selected cohort study where a group of randomly selected people were followed from before retirement. This study would reduce bias caused by the people who may be retiring early because of ill health or dementia risk factors.