Of the 2733 elders (1303 (48%) men and 1430 (52%) women), 984 (36%) were maintainers, 1314 (48%) minor decliners, and 435 (16%) major decliners. For each group, the predicted mean change over 4 years on the 3MS was 0.6 points for the maintainers, −1.1 points for minor decliners and −4.5 points for major decliners (). Compared to both groups of decliners, maintainers were younger, less likely to be female, to be Black, to have fair/poor self-rated health, and were better educated (all p<0.001, ). Minor decliners had slightly higher average BMI that the other two groups (p=0.008). Maintainers were less likely to be depressed than decliners (p=0.002), to report a history of stroke/TIA (p=0.005), hypertension, diabetes, or be APOE e4 carriers (all p<0.001). The three groups were similar in terms of self-reported history of MI.
Cognitive Slopes over Time for the Three Cognitive Groups
Baseline Characteristics by Cognitive Group.
We constructed Kaplan-Meier curves for death among 2592 participants who were alive and followed after the Year 5 visit (). We excluded 91 participants who were no longer alive in Year 5 and an additional 50 for whom we did not have vital status information. These excluded participants were more likely to be Black and to have had lower baseline cognitive scores (p< 0.05) but did not differ in terms of gender, age or education. There were a greater proportion of major decliners that were lost to follow-up on outcome data compared to minor decliners or maintainers (6% vs. 5% and 2% respectively, p=0.001). The mean follow-up time was 2.9 years and ranged from two weeks to 3.5 years. Kaplan-Meier estimates of death were lowest in the maintainer group (7% died by the Year 8 visit), intermediate among minor decliners (14% died), and highest among major decliners (20% died, ). In the unadjusted Cox model, maintainers had an estimated 52% lower hazard of mortality (Hazard Ratio (HR) = 0.48; 95% Confidence Interval (CI) = 0.36–0.63), whereas major decliners had a 48% increased hazard (HR = 1.48; 95% CI = 1.14–1.92) compared to minor decliners. These hazard ratios were slightly stronger and remained statistically significant after adjustment for age, gender, race, education, APOE e4, depression, baseline cognitive score, BMI, stroke/TIA, and time-dependent hypertension and diabetes (maintainers HR = 0.46; 95% CI = 0.34–0.64 and major decliners HR = 1.58; 95% CI = 1.16–2.16).
a. Kaplan-Meier Curves for Death According to Cognitive Group.
The Association between Cognitive Group and Risk of Death and Incident Disability.
We constructed Kaplan-Meier curves for disability among the 1837 participants with no reported disability through the Year 5 visit (). We excluded 91 participants who were no longer alive, 743 who reported disability at the Year 5 visit, and 62 for whom we did not have disability information during follow-up. The mean follow-up time was 2.6 years and ranged from 8 months to 3.7 years. As expected, incidence is clustered at the Year 6, Year 7, and Year 8 visits. Kaplan-Meier estimates of incident disability were lowest in the maintainer group (22% were disabled by the Year 8 visit), intermediate among minor decliners (29% were disabled), and highest among major decliners (40% were disabled). In the unadjusted Cox model, the hazard of incident disability was 26% lower among maintainers (HR=0.74; 95% CI=0.62–0.89), and 49% higher among major decliners (HR = 1.49; 95% CI = 1.19–1.86) compared to minor decliners. The magnitude of the association diminished slightly after adjustment for age, gender, race, education, APOE e4, depression, baseline cognitive score, BMI, stroke/TIA, and time-dependent hypertension and diabetes, but was still significant at a trend level (maintainers HR=0.84; 95% CI=0.69–1.04 and major decliners HR=1.37; 95% CI=1.06–1.78).
In order to determine if our results were robust to the cut-off points for major decline, we repeated our analyses using a cut-off for major decline of 1.5 standard deviations from the mean and found similar results. In addition, we determined if there were interactions of race or gender on cognitive trajectory group and risk of incident mortality or disability and did not find any statistically significant interaction.