Table 3.
Association between multimorbidity (≥2 chronic conditions) and subsequent risk of dementia as a function of age at onset of multimorbidity*
| Multimorbidity status | No of dementia cases/total No | Incidence rate per 1000 person years | Incidence rate difference (95% CI) per 1000 person years |
Hazard ratio (95% CI) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model 1† | Model 2† | Model 3† | ||||||||||
| At age 55 years (median follow-up 19.6 (IQR 15.6-25.1) years) | ||||||||||||
| 0 or 1 chronic condition | 587/9282 | 3.10 | 0 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | ||||||
| Multimorbidity | 51/655 | 4.67 | 1.56 (0.62 to 2.77) | 2.51 (1.87 to 3.35) | 2.47 (1.84 to 3.30) | 2.44 (1.82 to 3.26) | ||||||
| At age 60 years (median follow-up 14.8 (IQR 10.8-20.2) years) | ||||||||||||
| 0 or 1 chronic condition | 542/8497 | 4.04 | 0 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | ||||||
| Multimorbidity between 55 and 60 | 41/642 | 4.64 | 0.60 (−0.38 to 1.90) | 1.45 (1.05 to 1.99) | 1.40 (1.02 to 1.93) | 1.39 (1.01 to 1.91) | ||||||
| Multimorbidity before age 55 | 50/621 | 6.46 | 2.42 (1.09 to 4.12) | 2.57 (1.91 to 3.45) | 2.52 (1.88 to 3.39) | 2.46 (1.83 to 3.31) | ||||||
| P for trend | - | - | - | <0.001 | <0.001 | <0.001 | ||||||
| At age 65 years (median follow-up 10.1 (IQR 6.1-15.4) years) | ||||||||||||
| 0 or 1 chronic condition | 467/7444 | 5.59 | 0 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | ||||||
| Multimorbidity between 60 and 65 | 64/858 | 7.44 | 1.85 (0.64 to 3.39) | 1.55 (1.19 to 2.01) | 1.53 (1.17 to 1.99) | 1.51 (1.16 to 1.97) | ||||||
| Multimorbidity between 55 and 60 | 39/602 | 6.83 | 1.24 (−0.24 to 3.22) | 1.49 (1.08 to 2.07) | 1.44 (1.03 to 2.00) | 1.41 (1.01 to 1.96) | ||||||
| Multimorbidity before age 55 | 45/578 | 9.45 | 3.86 (1.80 to 6.52) | 2.57 (1.88 to 3.50) | 2.52 (1.85 to 3.44) | 2.46 (1.80 to 3.36) | ||||||
| P for trend | - | - | - | <0.001 | <0.001 | <0.001 | ||||||
| At age 70 years (median follow-up 6.7 (IQR 3.0- 11.4) years) | ||||||||||||
| 0 or 1 chronic condition | 352/5319 | 8.44 | 0 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | ||||||
| Multimorbidity between 65 and 70 | 71/894 | 10.78 | 2.34 (0.84 to 4.23) | 1.33 (1.03 to 1.72) | 1.32 (1.02 to 1.70) | 1.29 (1.001 to 1.67) | ||||||
| Multimorbidity between 60 and 65 | 50/683 | 10.76 | 2.32 (0.41 to 4.82) | 1.45 (1.07 to 1.95) | 1.41 (1.04 to 1.89) | 1.38 (1.02 to 1.86) | ||||||
| Multimorbidity between 55 and 60 | 32/470 | 10.96 | 2.52 (−0.09 to 6.10) | 1.50 (1.04 to 2.15) | 1.42 (0.98 to 2.04) | 1.36 (0.94 to 1.96) | ||||||
| Multimorbidity before age 55 | 37/417 | 17.38 | 8.94 (4.65 to 14.58) | 2.80 (1.99 to 3.94) | 2.71 (1.92 to 3.83) | 2.60 (1.84 to 3.67) | ||||||
| P for trend | - | - | - | <0.001 | <0.001 | <0.001 | ||||||
| Overall (multimorbidity and covariates as time varying measures; median follow-up 31.7 (IQR 31.1-32.6) years) | ||||||||||||
| 0 or 1 chronic condition | 189/4834 | 1.30 | 0 (reference) | 1 (reference) | 1 (reference) | 1 (reference) | ||||||
| Multimorbidity | 450/5261 | 2.89 | 1.59 (1.51 to 1.67) | 2.44 (2.04 to 2.91) | 2.44 (2.04 to 2.91) | 2.36 (1.97 to 2.81) | ||||||
IQR=interquartile range.
Multimorbidity defined as ≥2 chronic conditions out of 13 conditions: coronary heart disease, stroke, heart failure, diabetes, hypertension, cancer, chronic kidney disease, chronic obstructive pulmonary disease, liver disease, depression, mental disorders, Parkinson’s disease, and arthritis/rheumatoid arthritis.
Model 1: stratified on birth cohort (5 year groups) and adjusted for age (as time scale) and sex; model 2: model 1+ethnicity, education, and marital status; model 3: model 2+health behaviours (smoking, alcohol consumption, physical activity, and diet). Covariate measurement was concurrent with measure of multimorbidity