Figure 1 shows the PRISMA flow diagram. The initial search yielded 1,593 articles, 565 from PubMed, 538 from Web of Science, and 490 from CINAHL. We removed 496 duplicate articles, where the same article appeared in more than one database. Automated tools marked 74 articles as ineligible, which included 3 case reports, 28 review articles, and 43 articles without abstracts. We also excluded 95 additional records, such as 42 datasets, 25 preprints, 13 authorless articles, 9 patents, 3 genetic studies, 2 books, and 1 thesis. Subsequently, during title and abstract screening, 832 articles were excluded for not meeting the criteria. The remaining 96 articles underwent full-text screening. After excluding additional 16 articles, e.g., those not primarily using EHR data, or having small sample size, 80 articles remained for final analysis. A detailed list of these articles and extracted data is available in Supplementary Table 2 in the supplement.
Research Trend Over Time
Figure 2 illustrates the distribution of analyzed articles by publication year. It shows a notable increase in publications related to our topic over the past decade, indicating a growing trend in using EHR data to examine ADRD risk factors. Although our search spanned from 2010 to 2023, all included articles were published after 2014. More than one-quarter of the articles (n = 22, 27.5%) were published in 2022. It is important to note that our search was conducted up to April 2023; therefore, the total for that year does not reflect the full annual count.
Study Design
Out of the 80 articles reviewed, 77(96.3%) were longitudinal studies retrospectively conducted, comprising 70 cohort studies, six case-control studies, and one randomized control trial. Longitudinal studies had a median EHR duration of 16 years, calculated from the initial year to the final year of the EHR records utilized, regardless of individual patient follow-up time. Among these, 16 studies (20%) had EHR data spanning under 10 years, 39 studies (48.8%) ranged between 10 and 20 years, and 22 studies (27.5%) had data duration exceeding 20 years.
Methods for Statistical Analyses
In the statistical analysis, 76.3% of the studies (n = 61) predominantly used survival analysis to model and identify various risk or protective factors. Among these, most (n = 54, 88.5%) opted for the Cox proportional-hazards regression model,11 while some (n = 13, 21%) used the Fine-Gray model,12 often in combination. The Fine-Gray model was chosen for its ability to handle competing risks like death. Other statistical analysis methods included logistic regression, Chi-squared test, and analysis of variance (ANOVA).
EHR Datasets and Sources
The included articles utilized diverse datasets to examine ADRD risk factors. These datasets were derived either directly from EHR systems, such as Veterans Health Administration (VHA), or linked to EHR databases to incorporate specific variables or outcomes from external databases, such as the UK Biobank. Categorized by geographical location, almost half of the studies (46.3%, n = 37) used data from EHR systems within the United States (US), while 40% (n = 32) utilized datasets from the United Kingdom (UK). Additional countries represented in this review included Australia (n = 3),13–15 China (n = 3),16–18 Denmark (n = 3),19–21 the Netherlands (n = 3),20–22 Taiwan (n = 2),23, 24 Canada (n = 2),25, 26 and Sweden (n = 2).27, 28
In the US, the most frequently used EHR dataset was derived from the Kaiser Permanente’s EHR (11 studies), followed by the VHA (6 studies). The remaining 21 articles used databases from other US healthcare systems and commercial sources like TriNetX,29–31 IBM Explorys,32 and Optum.33 For studies utilizing UK datasets, the Whitehall II study34–39 (n = 8) and UK biobank40–46 (n = 7) cohorts were the most frequently used, linked to various UK EHR datasets, including the Hospital Episode Statistics,47 Scottish Morbidity Record data,48 and Patient Episode Database.40, 41, 46 Other frequently used databases in the UK studies included the Clinical Practice Research Datalink (n = 6)49–53 and the Health Improvement Network (THIN) (n = 4).21, 54, 55
EHR Dataset Sample Size
The studies employed datasets with varying sample sizes, from hundred to millions of patients. Only one study had fewer than 1000 patients.25 Twenty-six (32.5%) studies had datasets ranging from 1,000 to 10,000 patients; 46 (57.5%) studies had datasets with 10,000 to one million patients. Seven (8.8%) studies used datasets with over one million patients.
Outcomes and Measurements
Most studies (n = 67) examined multiple dementia subtypes, including AD, vascular dementia, Lewy body dementia (LBD), frontotemporal dementia (FTD), and mixed dementia. AD was consistently included in all studies, with nine studies exclusively focused on AD. The majority of these studies defined outcomes using standard coding systems, such as ICD codes (81.3%, n = 65), Read codes (11.3%, n = 9), and SNOMED-CT (2.5%, n = 2). Additionally, some studies employed alternative methods, including prescriptions for dementia medications,16, 18, 26, 33 cognitive function tests,25, 42, 56 referencing the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition),22, 57, 58 screening interviews,14, 56 and neuroimaging.42
Risk and Protective Factors
We summarized the analyzed risk factors in the reviewed articles, categorizing medical conditions and interventions into broad disease categories (Table 1). Other risk factors were classified into lifestyle, socioeconomic, environmental, and miscellaneous categories (Table 2).
Table 1
Summary of medical conditions and interventions from EHR-based studies in related to the risk of Alzheimer’s disease and related dementias.
| Medical conditions (n = 39) | Medical interventions (n = 25) |
Categories | No. of articles | Risk Factors/Exposures | No. of articles | Risk Factors/Exposures |
Cardiovascular and metabolic | 15 | Diabetes↑23, 26, 35, 60, 61 Hypoglycemia in diabetic patients↑16, 49, 56, 62 Hypertension↑23, 61, 63, 64↔26 Hypotension ↑20 High blood pressure variability ↑65 Coronary artery disease ↑23 Stroke ↑23 Hyperlipidemia ↑23 Dyslipidemia ↔26 Obesity ↑53 ↓40 ↔26 | 11 | Antihypertensive medications ↔26 Aspirin ↓30 Statins ↔26 Rosuvastatin ↓76 Anticoagulant ↓52a Telmisartan ↓24 Metformin ↔77 ↓33b Thiazolidinedione ↓78c Sulfonylurea ↑33, 78c Metformin and thiazolidinedione dual therapy ↓78c Sodium-glucose co-transporter 2 inhibitors ↓31 Carotid endarterectomy ↔27 Bariatric surgery ↑79 |
Infections, inflammatory, and immune-related | 11 | HIV ↑66, 67 E. coli ↑68e Herpes zoster ↓50 Covid-19 ↑29 Symptomatic herpes simplex virus infection ↓69 Common infections (sepsis, pneumonia, other LRTIs, UTIs and SSTIs) ↔42 Inflammatory/autoimmune conditions ↑45 Inflammatory Bowel Disease ↑32 High urate ↓40 Gout ↓55 | 5 | Tumor necrosis factor blocking agent ↓32, 80 Methotrexate ↓21, 80 NSAIDs ↑51 Antiherpetic medication ↓19 Immunomodulators ↓32 |
Neurological/ophthalmological conditions | 7 | Retinal vascular occlusion ↑58 ↔71 Visual impairment ↑41 Diabetic retinopathy ↑72 ↔73 Traumatic brain injury ↑74 Epilepsy ↑75 | 1 | Cataract extraction ↓57 |
Physical function and frailty | 5 | Low physical function ↑25 Physical inactivity ↔53 Underweight ↑20, 26, 40 ↔53 Low caloric intake ↔53 | | n/a |
Psychiatric | 4 | Depression ↑14, 26, 70 Psychotic disorder ↑15 | 4 | SSRI ↑81 ↓76 Trazodone ↑54e Benzodiazepines ↔22 |
Oncology | 2 | Cancer ↑45 Skin cancer ↓59 | 3 | Androgen deprivation therapy ↑82, 83 Aromatase inhibitor therapy versus tamoxifen ↔84d |
Other | 4 | Kidney disease ↑23, 36 Hip fracture ↑17 Osteoarthritis ↑26 | 3 | β-antagonists ↓18 Vitamin D ↓43 Omeprazole ↓76 |
Table 2
Summary of lifestyles, socioeconomic, psychosocial, environmental and other factors from EHR-based studies in related to the risk of Alzheimer’s disease and related dementias.
Categories | No. of articles | Risk Factors/Exposures |
Lifestyle, socioeconomic, psychosocial, environmental risk factors (n = 14) |
Lifestyle | 5 | Diet ↔37, 85 Healthy lifestyle ↓44 Smoking ↑26 Alcohol consumption ↑28 |
Socioeconomic | 5 | High education ↓86, 87 ↔38 Neighborhood disadvantage ↑ 26, 88 Low occupational position ↑38 |
Psychosocial | 2 | Social isolation ↑46 Social contact ↓39 Feeling of loneliness ↔46 |
Environmental | 3 | Birth in high stroke mortality states ↑89 Agent orange ↑90 Lithium level in drinking water ↑91 |
Others (n = 8) | | |
Others | 8 | Plasma protein ↑34 Lower testosterone ↑13 Higher brain age ↑103 Low Childhood IQ ↑104 ICU admission ↑105 Hispanic race ↑61 Sex ↔26 CRP genotype ↔45 Apolipoprotein E (APOE) genotype ↔45 |
Medical conditions
Out of the 80 articles reviewed, 39 (48.8%) explored the interplay between medical conditions and ADRD. Of them, 15 articles focused on cardiovascular and metabolic conditions, 11 on infections, inflammatory and immune-related conditions, 7 on neurological/ophthalmological conditions, 5 on physical function and frailty, 4 on psychiatric conditions, 2 on cancer,45, 59 and 4 on other risk factors like kidney disease,23, 36 osteoarthritis,26 and hip fracture.17
Cardiovascular and metabolic conditions: A significant finding in our analysis is the association of cardiovascular/metabolic conditions and ADRD risk. Diabetes, examined in several studies,23, 26, 35, 60, 61 and its common complication, hypoglycemia, identified as a risk factor,16, 49, 56, 62 are noteworthy. Extensive research using EHR data has explored blood pressure’s relationship with ADRD. Hypertension,23, 61, 63, 64 hypotension20 and blood pressure variability,65 all contribute to increased ADRD risk. Additional risk factors include coronary artery disease,23 stroke,23 and hyperlipidemia.23 Obesity’s impact is mixed: it has been identified as a risk factor in one study,53 suggested to have a potential protective effect in another,40 and found to have no impact in a third,26, 53 although this may be influenced by factors like age at assessment and frailty in underweight individuals.
Infections, inflammatory and immune-related conditions
HIV,66, 67 E. coli,68 and Covid-1929 have been identified as risk factors for ADRD. However, several common infections–such as sepsis, pneumonia, lower respiratory tract infections, urinary tract infections, and skin and soft tissue infections–did not exhibit increased ADRD risk.42 Regarding herpes viruses, one study observed a slightly decreased risk of dementia among individuals with symptomatic Herpes Simplex Virus 1 (HSV-1) infections untreated by antivirals and a more pronounced 25% decrease in those treated with antivirals.69 Another study detected a minor protective link between Herpes Zoster (HZ) and dementia, particularly in frail individuals and females, and only for mixed or unspecified dementia.50 Additionally, the inflammatory/autoimmune disease cluster was associated with elevated ADRD risk,45 including inflammatory bowel disease was also found as a risk factor.32 Both high urate40 and gout55 were associated with a decreased risk for ADRD, possibly due to uric acid’s antioxidant effects, which align with observations related to obesity.22
Psychiatric conditions
The interplay between depression and ADRD remains unclear. While some view depression as a symptom, others see it as a precursor. In our final analysis, three articles explored the link, and all identified a depression as a risk factor for ADRD.14, 26, 70 Additionally, psychotic disorders have been reported as a risk factor.15
Neurological/ophthalmological conditions
The eyes and brain also form crucial nodes in the ADRD risk network. Retinal vascular occlusion is linked to increased ADRD risk.58 Visual impairment, assessed by visual acuity, has also been linked to an elevated ADRD risk,41 although one study did not find this connection.71 The impact of diabetic retinopathy, a complication from diabetes, remains ambiguous, with one study indicating increased risk72 and another observed no effect.73 Traumatic brain injury74 and epilepsy75 are identified as risk factors.
Physical function and frailty
Frailty metrics are factors to consider in ADRD risk assessment. Underweight is identified as a risk factor for ADRD,20, 26, 40 although one study had a different finding.53 The protective effect of obesity, sometimes observed, could be related to avoiding the increased risk associated with being underweight.22 Low physical function, measured by grip strength and the Short Physical Performance Battery (SPPB), is linked to increased risk.25 However, another study did not find an association between physical inactivity or unintentional low caloric intake and ADRD risk.
Other medical conditions
Several studies have investigated a miscellany of medical conditions in related to ADRD. Cancer is noteworthy, with one study showing an elevated ADRD risk in the cancer disease cluster.45 In contrast, another study found that malignant melanoma and non-melanoma skin cancers were associated with a reduced ADRD risk, suggesting a protective effect.59 Additionally, kidney disease,23, 36 hip fracture,17 and osteoarthritis26 were identified as ADRD risk factors.
Medical interventions
In light of the risk posed by medical conditions to ADRD, researchers have examined various medical interventions to determine if they could mitigate the risk of ADRD. Of the 80 articles assessed, 25 (31.3%) analyzed the association between medical interventions and ADRD. Out of these, 11 were related to cardiovascular and metabolic interventions, 5 to immune, infection, and inflammatory interventions, 4 to psychiatric interventions, 3 to oncology, and 4 to other interventions.
Cardiovascular and metabolic-related interventions
Research has focused on treatments targeting cardiovascular and metabolic conditions to reduce ADRD risk. Medications such as rosuvastatin,76 telmisartan,24 anticoagulants,52 and aspirin,30 primarily for cardiovascular health, have proven effective in lowering ADRD risk. In diabetes management, metformin showed no association with incident dementia compared to no initial treatment within the first 6 months post-diagnosis.77 However, it presented a mild protective effect compared to sulfonylureas.33, 78 Conversely, thiazolidinedione monotherapy and combined therapy with metformin reduced ADRD risk compared to metformin alone.78 Sodium-glucose co-transporter 2 inhibitors decreased the risk of dementia in patients with atrial fibrillation and type 2 diabetes.31 Among surgical interventions, bariatric surgery increased ADRD risk,79 while carotid endarterectomy had no discernible impact.27
Immune, infection and inflammatory-related interventions
Immune, infection and inflammatory-related interventions, such as tumor necrosis factor blocking agent,80 methotrexate21 and antiherpetic medications,19 were found to have protective effects against ADRD, while nonsteroidal anti-inflammatory drugs (NSAIDs)51 were observed to increase the risk.
Psychiatric-related interventions
Studies had contradictory conclusions on the impact of the selective serotonin reuptake inhibitor (SSRI) antidepressant class on ADRD risk, with one suggesting it as a risk factor81 and the other as protective.76 Trazodone, another serotonergic antidepressant often used for insomnia, was reported as a neutral factor.54
Oncology and other Interventions
Androgen deprivation therapy was linked to an increased risk for ADRD in two studies by the same team.82, 83 However, aromatase inhibitor therapy and tamoxifen, used for hormone receptor-positive breast cancer, did not show a difference in dementia risk.84
Lifestyle, socioeconomic, psychosocial and environmental factors
EHR data have been utilized to examine the influence of lifestyle, socioeconomic, psychosocial, and environmental factors on ADRD. Out of the reviewed articles, 14 (17.5%) were related to this topic, with 5 articles focused on lifestyles, 5 on socioeconomic factors, 3 on environmental factors, and 2 on psychosocial factors.
Lifestyle
Both smoking26 and extensive alcohol consumption28 were identified as risk factors for ADRD. Conversely, a healthy lifestyle, including no current smoking, moderate alcohol consumption, regular physical activity, healthy diet, adequate sleep duration, less sedentary behavior, and frequent social contact, exhibited a protective effect against ADRD in patients with type II diabetes.44 However, diet alone was not found to be protective against ADRD.37, 85
Socioeconomic factors
Higher education showed neuroprotective effects in two of three studies on education and ADRD risk,86, 87 although the third study found no significant correlation.38 Neighborhood disadvantage26, 88 and low occupational position38 were associated to a higher risk of ADRD.
Psychosocial factors
Psychosocial factors such as social isolation have been identified as risk factors for ADRD.46 In contrast, frequent social contact appears to be a protective factor.39 Another metric, the “feeling of loneliness,” was not associated with an increased or decreased risk.46
Environmental factors
EHR data was used to analyze several environmental risk factors for ADRD. Being born in high stroke mortality states89 and exposure to Agent Orange among veterans90 were found to be associated with an increased risk of ADRD. Additionally, lithium levels in drinking water were associated with greater risk of dementia in women.91