Table 1.
Results of the systematic literature search.
| Authors | Population | IQ assessment | Outcome | FU time | Effect size | Comments |
|---|---|---|---|---|---|---|
| Cognitive Decline | ||||||
| Gow et al. (32) | Lothian Birth Cohort§ of 1921, Scotland, n=543 | Moray House Test, age 11 | Decline of performance in Raven's Matrices, Verbal Fluency, and Logical Memory, age 79-83 | 68-72 years | Latent cognitive functioning variable on decline of performance in any test: non-significant (latent variable growth curve modeling adj. sex, education, occupational social class, smoking, alcohol intake) | short observation period of only 4 years |
| Ritchie et al. (33) | Lothian Birth Cohort§ of 1921, Scotland, n=1091 | Moray House Test, age 11 | Decline of performance in subtests of Wechsler Adult Intelligence Scale, age 69-76 | 58-65 years | Moray House Test on decline of performance in any test: non-significant (latent growth curve model adj. sex, education, parental occupational status, own occupational status, deprivation of the residential area, physical fitness, APOE e4 status, smoking, body mass index, cardiovascular disease, hypertension, and diabetes) | |
| Salarirad et al. (34) | Lothian Birth Cohort§ of 1921, Scotland, n=106 | Moray House Test, age 11 | Decline of performance in Raven's Progressive Matrices, age 77-80 | 66-69 years | Moray House Test on decline of performance in the Raven's Progressive Matrices: non-significant (latent growth modeling adj. sex, age, brain white matter hyperintensities) | only one cognitive domain as outcome, adjusted only a few confounders, very small number of study participants |
| Staff et al. (35) | Lothian Birth Cohort§ of 1936, Scotland, n=388 | Moray House Test, age 11 | Decline of performance in Rey Auditory-Verbal Learning Test, age 64-77 | 53-66 years | Moray House Test on decline of performance in the Rey Auditory-Verbal Learning Test: non-significant (multilevel linear modeling adj. age, sex, practice, education, SES in childhood, mobility) | statistical reporting is not very comprehensive, only verbal learning test as outcome |
| Staff et al. (36) | Lothian Birth Cohort§ of 1921 and 1936, Scotland, n=751 | Moray House Test, age 11 | Decline of performance in Raven's Progressive Matrices, age 62-83 | 51-72 years | Moray House Test on decline in performance in the Raven's Progressive Matrices: non-significant (linear mixed modeling adj. for age and practice) | adjusted for only two confounders, research question of the paper is different than the research question of the review |
| Bourne et al. (37) | Lothian Birth Cohort§ of 1921 and 1936, Scotland, n=91; n=349 | Moray House Test, age 11 | Decline of performance in the Raven's Progressive Matrices, age 77-80 and age 64-66, mean interval 2 years | 53-69 years | Moray House Test on decline of performance in the Raven's Progressive Matrices: b = 0.13, p < 0.001 (multiple linear regression adj. gender, education, occupational status, smoker, alcohol, cohort, interval between testing) | only one cognitive domain as outcome, very small number of study participants, short observation period of only 2 years on average |
| Gow et al. (38) | Lothian Birth Cohort§ of 1921 and 1936, Scotland, n=496+1028 | Moray House Test, age 11 | Decline of performance in Moray House Test, age 79-86 | 68-75 years | Moray House Test on decline of performance in Moray House Test: non-significant (growth curve model adj. age, sex, social class, number of years of education, smoking status, alcohol consumption) | included only dementia-free individuals |
| Gow et al. (39) | Lothian Birth Cohort§ of 1921 (LBC), Scotland, n=548; National Survey of Health and Development (NSHD), Great Britain, n=3262 | Moray House Test, age 11; NSHD-devised test of verbal and non-verbal ability, age 15 | Decline of performance in Raven's Progressive Matrices, Verbal Fluency, Logical Memory, age 79, 83, 87; Verbal Memory, Search Speed, age 43, 53 | 32-76 years | Moray House Test on decline of performance in any test: non-significant (latent growth curve modeling adj. sex, social class, education, smoking, alcohol consumption) | adjusted only for a few confounders, model shape does not replicate the natural cognitive decline |
| Richards et al. (40) | National survey of health and development, Great Britain, n=2058 | Heim AH4 test, Watts-Vernon reading test, age 15 | Decline of performance in word list learning, visual search, age 43-53 | 28-38 years | Cognitive ability score on decline of performance in memory: men b=0.09, p = 0.005, women b=0.10, p < 0.001; Search speed: men b=0.13, p < 0.001, women b=0.08, p=0.01 (conditional models adj. memory and speed scores at 43 years, educational attainment, occupational social class, health indicators) | only linear analysis |
| Alzheimer's Disease and Related Dementias (ADRD) | ||||||
| Fritsch et al. (41) | Cleveland Longitudinal Aging Studies of Students (CLASS), OH, USA, n=396 | Otis Self-Administering Test of Mental Ability, age 15 | Dementia accord. DSM-IV and MCI (Modified telephone interview for Cognitive Status, proxy respondents), mean FU age 75 | about 60 years | Mental ability score on dementia: OR 0.55, CI 0.30–1.00; MCI: OR 0.46, CI 0.24–0.84 (logistic regression analysis adj. for sex, activity level, and education) | adjusted for only a few confounders, not enough socioeconomic variance because of affluent neighbourhood, only one FU point for following up on dementia prevalence |
| Huang et al. (42) | Project Talent–Medicare (PT-MED), USA n=85,763 | Battery of adolescent cognitive aptitude tests, age 14-18 | Dementia (Medicare-recorded codes), age 68-74 | 53-56 years | Cognitive ability score on dementia: men: OR 1.17, CI 1.04-1.32, women: OR 1.17; CI 1.04-1.31; Memory for words on dementia: men OR 1.16, CI 1.05-1.27, women OR 1.16, CI 1.05-1.28; Word function in sentences on dementia: men: OR 1.13, CI 1.03-1.25, women: OR 1.14, CI 1.03-1.27; Reading comprehension on dementia: men: OR 1.15, CI 1.02-1.29, women: OR 1.14, CI 1.02-1.27; Abstract reasoning on dementia: men: OR 1.12, CI 1.01-1.24, women: OR 1.13, CI 1.01-1.25; Introductory math on dementia: men: OR 1.15, CI 1.03-1.28, women: OR 1.11, CI 1.01-1.22; Arithmetic computation on dementia: men: OR 1.15, CI 1.04-1.27, women: OR 1.14, CI 1.03-1.26 (logistic regression stratified by sex, adj. birth year, race, adolescent SES, region of school, region of residence) | only Medicare participants, no validation of dementia diagnosis, advantage of the study is that it is a nationally representative study of American high school students |
| Osler et al. (43) | Danish Conscription Database, Denmark, n=666,986 men | Børge Prien Prøve draft board intelligence test, age 20 | Dementia (psychiatric/somatic hospital/registers, age 10-77 | Up to 57 years | Børge Prien Prøve draft board intelligence test on dementia: HR 1.74, CI 1.60–1.88; Vascular dementia HR 1.47, CI 1.31–1.56; Alzheimer's disease HR 1.07, CI 1.03-1.13; Twin brothers: HR 1.36, CI 1.08–1.73 (cox regression with age as time scale, Fine-Gray competing risk, adj. for height, education, age) | included only men eligible for military service, no validation of dementia diagnosis, adjusted only few confounders |
| Rantalainen et al. (44) | Helsinki Birth Cohort Study, Finland, n=2,785 men | Finnish Defence Forces Basic Intellectual Ability Test, age 20 | Dementia (hospital discharge/death registers, outpatient records), age 25-79 | Up to 59 years | Cognitive ability total score on dementia: HR 1.22, CI 0.97-1.54; Verbal ability on dementia: HR 1.14, CI 0.90-1.43, Arithmetic on dementia: HR 1.22, CI 0.96-1.53, Visuospatial abilities on dementia: HR 1.27, 1.00-1.60 (cox proportional hazard models adj. birthweight, mother's age, father's occupational status in childhood, attained level of education in adulthood, stroke, coronary heart disease) | included only men eligible for military, no validation of dementia diagnosis |
| Russ et al. (45) | Lothian Birth Cohort§ of 1921, Scotland, n=32,467 | Moray House Test, age 11 | Dementia (psychiatric/hospital/death records, subset primary care records), age 60-96 | 49-85 years | Moray House Test on dementia: women: HR 1.51, CI 1.29-1.76, men: HR 1.19, CI 0.98-1.44; women with IQ 100-114.9: HR 1.18, CI 1.03-1.34; women with IQ 85-99.9: HR 1.32, CI 1.15-1.51; men with IQ non-significant (hierarchical cox proportional hazards model with school- and county-level random effects adj. socioeconomic position, inverse probability weighting for survival) | adjusted for only a few confounders, no validation of dementia diagnosis, advantage of the study is that it adjusted for loss to follow-up by using weights and intensive record screening |
§, the Lothian Birth Cohorts of 1921 and 1936 are assessed at the age of 11, an assessment named the Scottish Mental Survey; adj., adjusted; CI, 95% confidence interval; OH, Ohio; OR, odds ratio; USA, United States of America; LBC, Lothian Birth Cohort; NSHD, National Survey of Health and Development.