Date Published: April 17, 2017
Publisher: Public Library of Science
Author(s): Leslie Grasset, Pierre Joly, Hélène Jacqmin-Gadda, Luc Letenneur, Jérôme Wittwer, Hélène Amieva, Catherine Helmer, Jean François Dartigues, Stephen D. Ginsberg.
To analyse the impact of a risk factor on several epidemiological indicators of death and dementia; the example of sport practice is presented.
A population of 3670 non-demented subjects living at home and aged 65 and older from the PAQUID study were followed for 22 years. Sport practice was documented at baseline. Dementia (according to DSM-III-R criteria) and death were assessed at each visit. Analyses were performed with an Illness-Death model, providing results on the risks of dementia and death, probabilities and life expectancies.
A total of 743 subjects (20.2%) participated in regular sport practice. During the follow-up, the proportion of death was lower in the elderly people practicing sport (EPPS), whereas the proportion of incident dementia cases was the same. The adjusted model showed a decreased risk of dementia (HR = 0.84 (0.72–1.00)) and of death for non-demented subjects (HR = 0.61 (0.51–0.71)) for EPPS but a similar risk of death with dementia in both sport groups. The probability of remaining alive without dementia was higher in EPPS, whereas the probability of dying was lower. The mean lifetime without dementia was 3 years higher for the EPPS, but the mean lifetime with dementia was the same.
A preventive measure on a protective factor that is more effective for preventing death than dementia could lead to an increased lifetime without dementia; however, the number of demented cases may remain unchanged, even if the risk of developing dementia is reduced. This dynamic is important to forecast the need for health care and social services for the elderly.
Dementia is a major cause of disability in the elderly and is a major fear in this period of life . Unfortunately, despite enormous research effort, no progress has been made in the curative treatment of dementia for approximately twenty years. Hopefully, some epidemiological studies showing a decrease in incidence and prevalence of dementia are in favour of possible successful prevention strategies [2–7]. Among the candidate factors for prevention, regular physical activity is one of the most promising [8–14]. However, the important question from an individual and collective point of view is: what results can we expect if we enhance regular physical activity and sport in the elderly?
Among the 3777 participants, 3670 were non-demented at baseline and provided answers to the leisure and social activities questionnaire (5 were missing values for sport practice status). Among them, 743 participated in regular sport practice (20.2%). The elderly people practicing sport (EPPS) were younger and had a higher level of education and better cognitive performance at baseline than the others (Table 1). The proportion of EPPS was higher in men than in women. During the 22 years of follow-up, 577 subjects (77.7%) from the EPPS group died and 168 were diagnosed with dementia (22.6%), whereas among those practicing no sport, 2556 died (87.3%) and 691 were diagnosed with dementia (23.7%). The mean MMSE score at time of diagnosis of dementia was 18.4 (5.4). The mean follow-up time was 11.57 (6.9) years.
With an illness-death model applied to the long-term follow-up of the PAQUID cohort, we found a higher probability of remaining alive without dementia in EPPS with a mean increase of 3.19 years of the mean lifetime without dementia in elderly subjects participating in sport compared to those not participating in sport. These 3.19 years represent an increase of almost 31.3% of the mean lifetime without dementia, which is substantial and of interest from an individual point of view. Estimations of “dementia-free life expectancy” have already been provided on the basis of prevalence data from the PAQUID cohort , which have been replicated in several countries [22–24]; however, the statistical analysis used did not allow study of the relationships with multiple risk factors or predictors of death and dementia.