Table 1. Characteristics of included studies.
| Author | Region | Study design | Sample size | Age, mean/range (years) | Exposure ascertainment | Exposure variable | Outcome | Disease ascertainment | RR (95% CI) | Adjustment |
|---|---|---|---|---|---|---|---|---|---|---|
| Abneret al, 2014 | The United States | Cohort | 649 | 72.9/≥60 | Single question | Head injury | AD | CERAD | 1.47(1.03–2.09)* | APOE-ε4, sex, age at death, presence of at least mild cerebral amyloid angiopathy, and whether AD was observed before death |
| 1.18(0.83–1.68)** | ||||||||||
| Bachmanet al, 2003 | The United States | Case-control | 2779 | 70.6/≥50 | Detailed interview | Head trauma | AD | NINCDS-ADRDA | 2.40(1.80–3.10) | Age, sex, education, head trauma, alcohol, and smoking |
| Boston et al, 1999 | The United Kingdom | Case-control | 396 | 82.9/≥75 | Not reported | Head injury | Dementia | MMSE and CAMDEX | 0.49(0.14–1.75) | Age, social class, age of left school, family history of dementia, history of falls, history of heart attack, history of hypertension, blood pressure, smoking, drinking, psychiatric history, cholesterol, and HDL |
| AD | 0.80(0.44–1.43) | |||||||||
| Broeet al, 1990 | Australia | Case-control | 340 | 78.1/52-96 | Detailed interview | Any head injury | AD | NINCDS-ADRDA | 1.33(0.46–3.83) | Age and sex |
| 1.75(0.52–5.88)* | ||||||||||
| Early head injury | AD | 1.60(0.53–4.84) | ||||||||
| 2.33(0.63–8.67)* | ||||||||||
| Dams-O'Connor et al, 2013 | The United States | Cohort | 4225 | 74.9/≥65 | Single question | TBI with LOC | Dementia | DSM-IV | 0.87(0.60–1.27) | Age, age-squared, gender, and education |
| AD | NINCDS-ADRDA | 0.95(0.65–1.38) | ||||||||
| Ferini-Strambiet al, 1990 | Italy | Case-control | 189 | 58.9/Not reported | Structured interview | Head injury | AD | Full-scale WAIS IQ and Blessed-Tomlinson-Roth Dementia Scale | 1.00(0.32–3.10) | Age, sex, residential area, education and social status |
| Fischer et al, 2008 | Austria | Cohort | 479 | 75.8/75-76 | Structured interview | Head trauma | AD | NINCDS-ADRDA | 0.46(0.16–1.31) | None |
| Forster et al, 1995 | England | Case-control | 218 | Not reported/<65 | Standardised interview | Any head injury | AD | NINCDS-ADRDA | 1.20(0.57–2.56) | Age and sex |
| Adult head injury | 1.50(0.68–3.41) | |||||||||
| Childhoodhead injury | 0.70(0.14–2.81) | |||||||||
| Fratiglioniet al, 1993 | Sweden | Case-control | 314 | Not reported/≥75 | Structured interview | TBI with LOC | AD | DSM-III-R and CDR | 0.30(0.10–1.20) | Age, sex, education, type of informant, and alcohol consumption |
| Gardner et al, 2014 | The United States | Cohort | 164661 | 71.6/≥55 | ICD-9 | TBI | Dementia | ICD-9 codes for the diagnosis of dementia | 1.26(1.21–1.32) | Age, sex, race, comorbidities, trauma mechanism, health care use, and trauma severity |
| Graves et al, 1990 | The United States | Case-control | 260 | 64.9/Not reported | Structured interview | Any head trauma | AD | DSM-III and NINCDS-ADRDA | 3.50(1.50–8.30) | Age and family history of AD |
| Head traumawith LOC | 2.90(1.10–7.53) | |||||||||
| Head trauma without LOC | 5.50(1.35–22.50) | |||||||||
| Guoet al, 2000 | The United States, Canada, and Germany | Case-control | 16901 | Not reported | Structured interview | Any head injury | AD | NINCDS-ADRDA | 2.70(2.20–3.30) | Gender and kinship |
| Head injury with LOC | 4.00(2.90–5.50) | |||||||||
| Head injury without LOC | 2.00(1.50–2.70) | |||||||||
| Lee et al, 2013 | Taiwan | Cohort | 720933 | Not reported/≥18 | ICD-9 | Mild TBI | Dementia | ICD-9-CM | 3.26(2.69–3.94) | Age, gender, urbanization level, socio-economic status, diabetes, hyperlipidemia coronary artery disease, history of alcohol intoxication, ischemic stroke, intracranial hemorrhage and Charlson comorbidity index |
| Li et al, 1992 | China | Case-control | 210 | 65.3/Not reported | Structured interview | Head injury with LOC | AD | NINCDS-ADRDA and ICD-10 | 1.00(0.09–11.03) | Age and sex |
| Lindsay et al, 2002 | Canada | Case-control | 4088 | 73.3/≥65 | Structured interview | Head injury | AD | NINCDS-ADRDA | 0.87(0.56–1.36) | Age, sex and education |
| Luukinenet al, 2005 | Finland | Cohort | 152 | 75.1/≥70 | Medical examination | TBI | Dementia | DSM-IV and the MMSE | 2.80(1.35–5.81) | Low educational status and sex |
| Mayeuxet al, 1993 | The United States | Case-control | 331 | 78.1/Not reported | Structured interview | Head injury with LOC | AD | National Institutes of Neurological Disorders and Stroke criteria | 3.70(1.40–9.70) | Gender, age, ethnic group, years of education, and head injury |
| McDowell et al, 1994 | Canada | Case-control | 793 | 80.9/≥65 | Structured interview | Head injury | AD | DSM-III-R and NINCDS-ADRDA | 1.66(0.97–2.84) | Age, sex, residence in community or institution, and education |
| Mehta et al, 1999 | The Netherlands | Cohort | 6645 | 68.9/≥55 | Detailed interview | Head trauma with LOC | Dementia | DSM-III-R and NINCDS-ADRDA | 1.00(0.50–2.00) | Age, education, and if applicable, gender |
| AD | 0.80(0.40–1.90) | |||||||||
| Dementia | 0.70(0.20–2.40)* | |||||||||
| AD | 0.90(0.20–4.00)* | |||||||||
| Dementia | 1.30(0.60–2.80)** | |||||||||
| AD | 0.90(0.30–2.40)** | |||||||||
| Nordstrom et al, 2014 | Sweden | Cohort | 811622 | 18.0/Not reported | ICD-8,9,10 | One mild TBI | Dementia | ICD-8, 9, 10 | 1.50(1.10–2.00)* | Age, place and year of conscription, overall cognitive function, alcohol intoxication, weight, height, knee extension strength, TBI in parents, dementia in parents, income, educational level, systolic blood pressure, drug intoxication, depression, and cerebrovascular disease |
| AD | 1.00(0.50–2.00)* | |||||||||
| At least two mild TBI | Dementia | 1.80(1.10–3.00)* | ||||||||
| AD | 2.50(0.80–8.10)* | |||||||||
| One severe TBI | Dementia | 2.30(1.50–3.60)* | ||||||||
| AD | 0.70(0.10–5.20)* | |||||||||
| O'Meara et al, 1997 | The United States | Case-control | 691 | 78.0/≥60 | Detailed interview | Head injury with LOC | AD | DSM-III-R and NINCDS-ADRDA | 2.10(1.10–3.80) | None |
| 4.20(1.50–11.50)* | ||||||||||
| 1.10(0.50–2.60)** | ||||||||||
| Ogunniyiet al, 2006 | The United States | Case-control | 523 | 77.9/Not reported | Screening interview | Head injury | AD | NINCDS-ADRDA | 0.55(0.21–1.45)) | Age and gender |
| Nigeria | 470 | 79.2/Not reported | 1.36(0.30–6.30)) | |||||||
| Plassmanet al, 2000 | The United States | Cohort | 1776 | 72.9/Not reported | Medical record | Head injury | Dementia | DSM-III-R and NINCDS-ADRDA | 2.46(1.43–4.24)* | Years of education and age |
| AD | 2.16(1.10–4.23)* | |||||||||
| Rasmussonet al, 1995 | The United States | Case-control | 102 | 71.0/Not reported | Standardized interview | Head injury | AD | Not reported | 13.75(1.76–107.52) | None |
| Rippon et al, 2006 | The United States | Case-control | 1498 | 68.2/Not-reported | Standardized interview | Head injury | AD | NINCDS-ADRDA | 1.00(0.70–1.60) | ε4 status, age, gender, and education |
| Salibet al, 1997 | The United Kingdom | Case-control | 538 | 75.1/>65 | Head injury | DementiaAD | NINCDS-ADRDA | 2.46(1.42–4.10) | Age, sex, time lag between head injury and onset, duration of condition and family history of dementia | |
| 1.52(0.98–2.35) | ||||||||||
| 2.10(1.10–4.10)* | ||||||||||
| 1.38(0.74–2.60)** | ||||||||||
| Schofield et al, 1997 | The United States | Cohort | 271 | 75.3/≥60 | Detailed interview | Head injury with LOC | AD | NINCDS-ADRDA | 1.05(0.34–3.22) | Sex and education |
| Suhanovet al, 2006 | Russia | Case-control | 520 | 69.3/40-89 | Structured interview | Head injury with LOC | AD | NINCDS-ADRDA | 1.70(1.00–2.80) | Family history of dementia, family history of parkinsonism, and hypertension |
| Sundstromet al, 2007 | Sweden | Case-control | 543 | 72.8/40-85 | Medical record or interview | Mild head injury | Dementia | DSM-IV | 0.90(0.40–1.80) | Age and gender |
| Tsolakiet al, 1997 | Greece | Case-control | 134 | Not reported/>70 | Structured interview | Head trauma | AD | DSM-IV and NINCDS-ADRDA | 1.07(0.47–2.45) | Age and gender |
| vanDuijnet al, 1992 | The Netherlands | Case-control | 396 | 56.8/Not reported | Structured interview | Head trauma with LOC | AD | NINCDS-ADRDA | 1.60(0.80–3.40) | Age, sex, dementia in first-degree relatives and education |
| 2.50(0.90–7.00)* | ||||||||||
| 0.90(0.30–2.80)** | ||||||||||
| Wang et al, 2012 | Taiwan | Cohort | 269550 | 40.8/≥15 | ICD-9 | TBI | Vascular dementia | ICD-9-CM | 1.32(1.06–1.65) | Sex, age group, year of index healthcare use, stroke, diabetes, hyperlipidaemia, hypertension, coronary heart disease, heart failure and arterial fibrillation |
| Unspecific dementia | 1.74(1.62–1.88) | |||||||||
| AD | 1.49(1.08–2.07) | |||||||||
RR = relative risk. CI = confidence interval. AD = Alzheimer’s disease. CERAD = The Consortium to Establish a Registry for Alzheimer's Disease. MMSE = Mini-Mental State Examination test. CAMDEX = Cambridge Examination for Mental Disorders of the Elderly. TBI = traumatic brain injury. LOC = loss of consciousness. DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. NINCDS-ADRDA = National Institute of Neurological and Communicative Diseases and Stroke-Alzheimer Disease and Related Disorders Association. DSM-III-R = Diagnostic and Statistical Manual of Mental Disorders, third edition revised. ICD-9 = International Classification of Diseases, Ninth Revision. CDR = The Clinical Dementia Rating scale.
* Relative risks and 95% CIs for males.
** Relative risks and 95% CIs for females.