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Randomized controlled trials (RTC) are the gold standard in medicine. In dementia care, however, relying only on RCTs leaves out a large amount of strong research that reflects real-world complexity.
Clinicians often hesitate to trust evidence about how well a treatment works unless it comes from an RTC. In medical training, RCTs are taught as the most reliable kind of study, shaping a medical culture in which people believe that strong causal claims must come from randomized studies.
These beliefs also affect how clinicians view major reports. For example, some are unsure about using the 2024 Lancet Commission on Dementia Prevention, Intervention and Care because its recommendations are based on many types of studies, not only RCTs. In an RCT, people are randomly assigned to different groups so researchers can see whether a treatment itself caused a change in outcomes. While this design is powerful, relying on it too heavily can make clinicians miss other kinds of evidence that reflects the real-world complexity of dementia. Dementia develops over many years and is influenced by social, environmental and medical factors that interact with each other. If we look only at RCTs, we miss valuable information about what works, for whom, in which situations and why – questions that patients and primary care teams face every day.
RCTs are still essential when we want to test a very specific medical question. For example, RCTs of the Alzheimer’s drugs Lecanemab and Donanemab showed modest but meaningful slowing of decline over about 18 months, although they also showed risks like brain imaging changes linked to amyloid treatments that must be monitored. These RCTs were well designed to test whether a particular drug affects a specific biological pathway.
But dementia prevention is different. It does not follow a single pathway. Risk builds up from everyday factors across a lifetime – such as physical activity, learning, social connection, hearing, vision, sleep, mental wellbeing and environment – all play a vital role in maintaining brain health. These factors interact in complicated ways. No single RCT can capture all of this. Expecting multi-domain prevention to meet the same standards as drug trials misunderstands the problem.
There is randomized evidence for prevention. For example, in the U.S. POINTER RCT, more than 2,000 older adults at higher risk for cognitive decline took part in a structured lifestyle program. Over two years, the group receiving more intensive support showed greater improvement in thinking skills than the group with a lighter program. This supports the Lancet Commission’s idea that prevention works best as a combined package, not as one single action.
The 2024 Lancet Commission therefore uses an “integrative” model of evidence. Instead of relying on only one type of study, it looks at RCTs, long-term observational studies, meta-analyses, natural experiments, implementation research and grey literature. It uses a realist approach that focuses on practical questions: What works? For whom? In what context? And why? This approach does not replace RCT evidence – especially for drug treatments – but adds important insight for real-world care. It helps clinicians translate evidence into action that fits a patient’s life circumstances, including cost, transportation, caregiving duties, physical ability and local resources.
The GRADE Working Group now supports combining randomized and non-randomized evidence in a structured way. GRADE Guidance 44 offers four steps: define the goal and thresholds; check whether RCTs and non-RCTs show similar effects; identify which evidence-quality factors matter most; and decide whether to combine or separate the evidence.
Examples show why this broader view is important. The ACHIEVE RCT found that hearing treatment slowed cognitive decline in people at higher risk for dementia, but not when all participants (including low-risk individuals) were analyzed together. The SPRINT MIND RCT demonstrated that intensive blood pressure control reduced mild cognitive impairment and suggested a possible reduction in dementia. But putting these findings into practice depends on system-level factors like medication adherence and follow-up capacity.
Environmental factors also highlight the need for a wide evidence lens. Long-term exposure to fine particulate air pollution (PM2.5) is linked to higher dementia risk and greener environments are linked with lower risk. These exposures cannot be tested in RCTs, yet they have major population-level effects. In this sense, policies on urban design, transportation and environmental regulation become dementia-prevention strategies.
Education is another example. Higher educational attainment and lifelong learning seem to build “cognitive reserve,” helping the brain cope better with disease. Because education shapes lifelong risk, investing in literacy and equal access to schooling is a public health strategy for prevention of dementia. But waiting for RCTs on schooling would be unrealistic and unethical.
Clinicians can act now using three principles:
- Use the full range of evidence and present dementia prevention as a package of small actions that add up over time.
- Apply context–mechanism–outcome thinking. Ask: in this person’s life, what can we activate right now? Examples include affordable hearing aids, self-monitoring of blood pressure in pharmacies or local walking or social programs.
- Start with feasibility. Ask early about barriers – cost, time, transportation, caregiving – and design small, sustainable steps. Prevention should feel supportive, not blaming. Team-based care and community partnerships help patients follow through.
A lot of people want clear, reliable information they can use in their everyday lives. Increase Your Brainability: A Brief Guide of 33 Actions to Reduce Your Risk and Impact of Dementia (ed. note: Dr. Chambers is one of the authors) takes the findings of the Lancet Commission and turns them into simple steps that anyone can follow at home. Many of the same actions that lower the risk of dementia also help prevent heart disease, stroke, diabetes, depression and physical weakness. The book is not a replacement for medical care, but may help people take meaningful steps between appointments.
The overall message is clear: the Lancet Commission’s broad and integrative approach is a strength. Dementia risk comes from interacting with biological, social and environmental factors. Evidence that reflects this complexity – using both RCTs and high-quality non-RCT studies – provides the best foundation for action. GRADE 44 recognizes that for public health and system-level interventions, non-randomized evidence often includes essential information RCTs cannot provide. When findings are consistent, and mechanisms make sense, clinicians and policymakers can act confidently. This means clinicians can counsel effectively today, policymakers can remove practical barriers and patients and caregivers can make meaningful changes at home.
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Previously Published on healthydebate.ca with Creative Commons License
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