Study Population

The study design and recruitment methods of the Bronx Aging Study have been described previously.19,20 Briefly, the study enrolled English-speaking subjects between 75 and 85 years of age who resided in the community. Criteria for exclusion included severe visual or hearing impairment and a previous diagnosis of idiopathic Parkinson's disease, liver disease, alcoholism, or known terminal illness. Subjects were screened to rule out the presence of dementia at base line and were included if they made eight or fewer errors on the Blessed Information–Memory–Concentration test.19-21 This test has a high test–retest reliability (0.86), and its results correlate well with the stages of Alzheimer's disease.22,23 At the inception of the study, the cohort was middle-class, most subjects were white (91 percent), and the majority were female (64 percent). Written informed consent was obtained at enrollment. The local institutional review board approved the study protocol.

The study enrolled 488 subjects between 1980 and 1983. Subjects underwent detailed clinical and neuropsychological evaluations at enrollment and at follow-up visits every 12 to 18 months. The potential study period consisted of the 21-year period from 1980 to 2001. We excluded 2 subjects without documented leisure activities and 17 subjects who moved or declined to return for follow-up. After these subjects had been excluded, 469 subjects (96.1 percent) were eligible. In 1992, 73 surviving subjects were still having study visits in our current project, the Einstein Aging Study.

Clinical Evaluation

During the study, subjects were interviewed with the use of a structured medical-history questionnaire and were examined by study clinicians.19,20 Functional limitations on 10 basic and instrumental activities of daily living were rated on a 3-point scale for each activity (range of total scores, 10 to 30 points), with 1 point indicating “no limitation,” 2 points indicating “does activity with difficulty,” and 3 points indicating “unable.”19,20 A spouse or family member accompanied most subjects or was contacted for confirmation of the history.

Neuropsychological Evaluation

An extensive battery of neuropsychological tests was administered at study visits.18-20 We examined performance on the Blessed Information–Memory–Concentration test (range of scores, 0 to 33),21 the verbal and performance IQ according to the Wechsler Adult Intelligence Scale,24 the Fuld Object-Memory Evaluation (range of scores, 0 to 10),25 and the Zung depression scale (range of scores, 0 to 100).26 These tests were used to inform the diagnosis of dementia at case conferences.

Leisure Activities

At base line, subjects were interviewed regarding participation in 6 cognitive activities (reading books or newspapers, writing for pleasure, doing crossword puzzles, playing board games or cards, participating in organized group discussions, and playing musical instruments) and 11 physical activities (playing tennis or golf, swimming, bicycling, dancing, participating in group exercises, playing team games such as bowling, walking for exercise, climbing more than two flights of stairs, doing housework, and babysitting). Subjects reported the frequency of participation as “daily,” “several days per week,” “once weekly,” “monthly,” “occasionally,” or “never.” We recoded these responses to generate a scale with one point corresponding to participation in one activity for one day per week. The units of the scales are thus activity-days per week; the scales were designed to be intuitively meaningful to clinicians and elderly persons and to be useful in the design of intervention studies or public health recommendations. For each activity, subjects received seven points for daily participation; four points for participating several days per week; one point for participating once weekly; and zero points for participating monthly, occasionally, or never. We summed the activity-days for each activity to generate a cognitive-activity score, ranging from 0 to 42, and a physical-activity score, ranging from 0 to 77.

The estimates of the overall level of participation were consistent with good test–retest reliability for scores obtained on entry and at the next visit a year later on the cognitive-activity scale (Spearman r = 0.518, P=0.001) and the physical-activity scales (Spearman r = 0.410, P=0.001). There was no direct measurement of the time spent in activities, although participation was verified by family members or friends. The scores were not correlated with age. Scores on the cognitive-activity scale correlated with scores on the Blessed test21 (Spearman r = –0.286, P=0.001), but not functional status (Spearman r = –0.042, P=0.77). Scores on the physical-activity scale correlated with functional status (Spearman r = –0.293, P=0.001) but not with scores on the Blessed test (Spearman r = –0.021, P=0.65).21

Diagnosis of Dementia

At study visits, subjects in whom dementia was suspected on the basis of the observations of members of the study staff, results of neuropsychological tests, or a worsening of the scores on the Blessed test21 by four points or a total of more than seven errors underwent a workup including computed tomographic scanning and blood tests.19,20 A diagnosis of dementia was assigned at case conferences attended by study neurologists, a neuropsychologist, and a geriatric nurse clinician, according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders, third edition (DSM-III) or, after 1986, the revised third edition (DSM-III-R).27-29 Updated criteria for the diagnosis of dementia and particular types of dementia were introduced after the study had begun.

To ensure uniformity of diagnosis, all cases were discussed again at new diagnostic conferences held in 2001 and involving a neurologist and a neuropsychologist who had not participated in diagnostic conferences between 1980 and 1998.29 Dementia was diagnosed according to the DSM-III-R criteria.28 Reduced participation in leisure activities was used to assess functional decline, but the leisure-activity scales were not available to the raters assessing such decline. Disagreements between raters were resolved by consensus after the case was presented to a second neurologist, with blinding maintained. Cases of dementia were classified according to the criteria for probable or possible Alzheimer's disease published by the National Institutes of Neurological Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association30 and the criteria for probable, possible, or mixed vascular dementia published by the Alzheimer's Disease Research Centers of California.31

Statistical Analysis

Continuous variables were compared with use of either an independent-samples t-test or the Mann–Whitney U test, and categorical variables were compared with use of the Pearson chi-square test.32 In primary analyses, we studied the association between cognitive and physical activities and the risk of dementia and specific types of dementia using Cox proportional-hazards regression analysis to estimate hazard ratios, with 95 percent confidence intervals.33 The time to an event was defined as the time from enrollment to the date of a diagnosis of dementia or to the final contact or visit for subjects without dementia. All multivariate models reported include the following covariates unless otherwise specified: age at enrollment, sex, educational level (high school or less vs. college-level education), presence or absence of chronic medical illnesses, and base-line scores on the Blessed test. Presence of the following self-reported chronic medical illnesses was individually entered in the models: cardiac disease (angina, previous myocardial infarction, or cardiac failure), hypertension, diabetes mellitus, stroke, depression, and hypothyroidism. We also divided the study cohort into thirds on the basis of their scores on the two activity scales and determined the risk of dementia according to these groups. We examined the role of individual leisure activities by comparing subjects who participated in an activity several days or more per week (frequent participation) with subjects who participated weekly or less frequently (rare participation) and, in the full models, adjusted for participation in other leisure activities.

In secondary analyses, we examined the influence of base-line cognitive status and possible preclinical dementia. First, we sequentially excluded from the full models subjects in whom dementia developed during the first two, four, seven, and nine years of follow-up in order to avoid confounding by a possible influence of preclinical dementia on participation in leisure activities. Second, we used linear mixed models controlled for age, sex, and educational level to assess the relation between cognitive activities and base-line cognitive status and the annual rate of change in cognitive status.34 We analyzed verbal IQ as well as specific cognitive domains, including episodic memory (with the Buschke Selective Reminding test [range of scores, 0 to 72, with lower scores indicating worse memory]35 and the Fuld Object-Memory Evaluation25) and executive function (with the Digit–Symbol Substitution subtest of the Wechsler Adult Intelligence Scale [range of scores, 0 to 90, with lower scores indicating worse cognition]).24 Each model included terms for the cognitive-activity score, time, and the interaction between the two. The assumptions of the models were examined analytically and graphically and were adequately met.