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Home › Research › What the research found › Every row

Every row of the evidence table

One row per finding: what was tested, which way the result went, and how the study was built. The answer by area, and where the studies disagree, are on the main page.

Every row

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Area All 382 Care, carers and services 140 Medicines 85 Genes (not modifiable) 35 All modifiable factors together 27 Diet and supplements 23 Exercise and activity 21 Sleep, mood and social life 19 Hearing and vision 8 Alcohol, tobacco and cannabis 6 Infection and vaccination 5 Heart and metabolic health 4 Injury, delirium and falls 4 Environment 3 Cognitive activity 2
Question Both Prevention 190 Treatment 192
Direction Any Benefit 144 Harm 105 No effect 38 Mixed 37 No direction reported 58
Design Any meta-analysis 57 randomised trial 44 phase 3 trial 15 systematic review 9 phase 2 trial 10 cohort study 136 phase 1 trial 2 cross-sectional study 31 case-control study 14 modelling study 20 regulatory decision 7 company announcement 1 coverage determination 1 None 35
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Showing 6 of 382 rows. One row per study per exposure: a study that tested two different things appears twice, once for each.

Scroll the table sideways to see every column.

Research and outcomes, 6 rows. Every row links to its source.
Exposure Question Direction Outcome measured Design People Effect size, as the source reported it Source
Alcohol Alcohol, tobacco and cannabis Prevention Harm
why

The key point: the observational analysis showed light drinking looking protective, but the genetic (Mendelian randomisation) analysis did not, which the authors read as the protective appearance coming from people cutting down in early dementia.

 Incident dementia cohort study 559,559 Mendelian randomisation OR 1.15 per SD increase in log drinks/week (95% CI 1.03-1.27); alcohol use disorder HR 1.51 (1.42-1.60) BMJ Evidence-Based Medicine 2026
✓ Peer-reviewed PMID 40987604
Alcohol Alcohol, tobacco and cannabis Prevention Benefit
why

This one reports light-to-moderate drinking as protective (HR 0.65) against non-drinking, and it flatly contradicts the Mendelian randomisation evidence. Infrequent drinkers were excluded, and non-drinkers include people who stopped for health reasons.

 Incident dementia over a median 13.7 years cohort study 296,715 Low-moderate drinking HR 0.65 (95% CI 0.59-0.73) vs non-drinking European Journal of Epidemiology 2025
✓ Peer-reviewed PMID 41014391
Alcohol Alcohol, tobacco and cannabis Prevention Mixed
why

Sustained mild and moderate drinking carried lower risk than not drinking, sustained heavy drinking higher risk, and cutting down from heavy to moderate lower risk. Observational, with the same abstainer problem.

 Incident all-cause dementia over a mean 6.3 years cohort study 3,933,382 Sustained heavy drinking aHR 1.08 (95% CI 1.03-1.12); heavy-to-moderate reduction aHR 0.92 (0.86-0.99) JAMA Network Open 2023
✓ Peer-reviewed PMID 36745453
Alcohol Alcohol, tobacco and cannabis Prevention Mixed
why

U-shaped: long-term abstainers had 47% higher risk than moderate drinkers, and above 14 units a week each extra 7 units raised risk by 17%. Neither end of the range looks like a benefit of drinking.

 Incident dementia over 23 years cohort study 9,087 Abstinence in midlife vs 1-14 units/week: hazard ratio 1.47 (95% CI 1.15 to 1.89). Among those drinking >14 units/week, "a 7 unit increase in alcohol consumption was associated with a 17% (95% confidence interval 4% to 32%) increase in risk of dementia". CAGE score >2: HR 2.19 (1.29 to 3.71); alcohol-related hospital admission: 4.28 (2.72 to 6.73) BMJ 2018
✓ Peer-reviewed PMID 30068508
Cannabis use Alcohol, tobacco and cannabis Prevention Harm
why

The exposure is cannabis use severe enough to need hospital care, not cannabis use in general, and the comparison is against other acute-care patients as well as the general population.

 New dementia diagnosis cohort study 6,086,794 Adjusted HR 1.23 (95% CI 1.09-1.39) vs all-cause acute care; 1.72 (95% CI 1.38-2.15) vs general population JAMA Neurology 2025
✓ Peer-reviewed PMID 40227745
Smoking Alcohol, tobacco and cannabis Prevention Benefit
why

Direction is for QUITTING. Risk approached that of never-smokers and levelled off about seven years after quitting; weight gain after quitting narrowed the advantage. The authors flag residual confounding.

 Incident dementia over a median 9.9 years cohort study 32,802 HR 0.84 (95% CI 0.73-0.95) for quitting during follow-up vs continuing to smoke Neurology 2026
✓ Peer-reviewed PMID 42160746

How this table was built, and where it is weak →