“[Abstract methods] we searched PubMed and Web of Science from inception to March 12, 2020, and included interventions that: successfully targeted any of nine prespecified potentially modifiable risk factors (hypertension, diabetes, hearing loss, obesity, physical inactivity, social isolation, depression, cigarette smoking, and less childhood education); had robust evidence that the intervention improved risk or risk behaviour; and are feasible to enact in an adult population. We established when in the life course each intervention would be delivered. We calculated dementia incidence reduction from annual incidence of dementia in people with each risk factor, and population attributable fraction for each risk, corrected for risk factor clustering, and how effectively the intervention controls the risk factor. [..] We estimated annual total expenditure on the fully operational intervention programme in England.
[Abstract findings] We found effective interventions for hypertension, smoking cessation, diabetes prevention, and hearing loss. Treatments for stopping smoking and provision of hearing aids reduced cost. Treatment of hypertension was cost-effective by reference to standard UK thresholds. The three interventions when fully implemented would save £1·863 billion annually in England, reduce dementia prevalence by 8·5%, and produce quality-adjusted life-year gains. The intervention for diabetes was unlikely to be cost-effective in terms of effect on dementia alone.
[Article results] We identified four potential interventions with robust evidence of effectiveness in reducing dementia incidence.
The first potential intervention is for mid-life hypertension. Several studies have shown that antihypertensives treat hypertension effectively, with some showing effects on dementia. A reduction in the risk of dementia is observed even if blood pressure remains above hypertensive thresholds. Calculations of cost used three antihypertensives together if necessary, as recommended by NICE, assuming this would achieve sufficient hypertensive control to eliminate excess dementia risk of mid-life hypertension.
The second potential intervention is for smoking in later life. Smoking cessation reduces risk of dementia. We identified any form of nicotine replacement therapy as the most effective intervention because it is a feasible intervention and commonly used. A meta-analysis showed that the RR of abstinence from smoking for any form of nicotine replacement therapy relative to control was 1·60, with effects largely independent of therapy duration, additional support intensity, or setting. [..] There were ten trials with 2751 participants, of whom 323 quit, but 40% of these resumed smoking, leading to a permanent quit rate of 7%.
The third potential intervention is for later-life type 2 diabetes. We identified a lifestyle change intervention to prevent diabetes because to our knowledge there is no evidence that treating diabetes reduces the risk of developing dementia compared with untreated diabetes.
[..] The fourth potential intervention is for mid-life hearing loss. We chose provision of a hearing aid as the intervention since increasing evidence from longitudinal studies shows that initiating hearing aid use slows memory decline, and continued use reduces dementia risk to that of people without hearing impairment. People with hearing impairment who do not use hearing aids remain at an increased risk of dementia. We assume those with hearing aids avoid the excess risk associated with hearing loss.
[Article discussion] there was an absence of evidence for feasible interventions for the whole obese population that resulted in lowering BMI to below the obesity threshold. The third was depression; to our knowledge, no evidence suggests that treating depression reduces risk of developing dementia, and no identified interventions exist to prevent depression in the general population. The final two risk factors were low social contact and physical inactivity; evidence for both risk factors was insufficient for effective interventions to be modelled.”
Full article, Mukadam N, Anderson R, Knapp M et al. The Lancet Healthy Longevity 2020 October.