Editor's note: This popular story from the Daily Briefing's archives was republished on Jan. 11, 2021.
A new report from the Lancet Commission on Dementia Prevention identifies 12 risk factors linked to 40% of all dementia cases, adding three new risk factors to the Commission's original 2017 report, Sue Hughes reports for Medscape.
The 2017 report identified nine modifiable risk factors that were estimated to account for a third of all dementia cases. The Lancet Commission included those same nine risk factors in this year's report, as well, but the Commission updated the weighted population attributable fraction attributed to the risk factors. They are:
- Midlife hearing loss, accounting for 8.2% of dementia cases;
- Not completing secondary education, accounting for 7.1% of cases;
- Later-life smoking, accounting for 5.2% of cases;
- Later-life depression, accounting for 3.9% of cases;
- Later-life physical inactivity, accounting for 1.6% of cases;
- Later-life social isolation, accounting for 3.5% of cases;
- Midlife hypertension, accounting for 1.9% of cases;
- Later-life diabetes, accounting for 1.1% of cases; and
- Midlife obesity, accounting for 0.7% of cases.
The Commission also included three new modifiable factors in the updated report:
- Excessive alcohol intake in midlife, accounting for 0.8% of cases;
- Traumatic brain injury (TBI) in midlife, accounting for 3.4% of cases; and
- Air pollution in later life, accounting for 2.3% of cases.
Evidence behind new factors
Gill Livingston, lead author of the report and a professor at University College London, said, when the original report was published in 2017, the Commission knew "with the nine risk factors that they would only be part of the story and that several other factors would likely be involved." She added, "We now have more published data giving enough evidence" to justify the addition of the three new factors.
Regarding alcohol intake, the report stated that there is an "increasing body of evidence is emerging on alcohol's complex relationship with cognition and dementia outcomes from a variety of sources including detailed cohorts and large-scale record-based studies." For instance, the report cited one French study involving more than 31 million people that found alcohol use disorders were linked to a threefold increase in dementia risk. However, the report also cited research indicating that moderate alcohol consumption may reduce risk.
Livingston clarified that the commission is not "saying it is bad to drink, but we are saying it is bad to drink more than 21 units [of alcohol] a week."
Regarding TBI—which is generally caused by motor vehicle injuries, military exposures, firearms, falls, or recreational sports, such as boxing and horse riding—the report cited multiple nationwide studies linking such injuries with significantly increased risk for long-term dementia.
Livingston said that, as with alcohol consumption, the Commission is not "advising against partaking in sports, as playing sports is healthy," but rather "urging people to take precautions to protect themselves properly."
Meanwhile, for air pollution, the report cited animal studies that have found airborne particulate pollutants can accelerate neurodegenerative processes. Moreover, high concentrations of nitrogen dioxide, as well as fine ambient particulate matter from exhaust in traffic and residential wood burning, have been linked to increased incidents of dementia, the report said.
How to curb your risk of dementia
The report also listed nine recommendations from the Commission for lawmakers and individuals to reduce dementia risk, including population-based and individually targeted recommendations. Those recommendations included, on the population level, calls to:
- Prioritize childhood education;
- Implement social public health policies that curb hypertension risk;
- Develop policies that bolster social, cognitive, and physical activity throughout life;
- Assess peoples' risks for hearing loss throughout life;
- Curb TBI risk in relevant settings;
- Implement national and international policies to lessen populations' exposure to air pollution; and
- Strengthen national and international efforts to curb exposure to smoking, reduce uptake, and support cessation.
For individuals, the Commission called on people to:
- Aim for a systolic blood pressure of 130 mm Hg or lower beginning in midlife;
- Use hearing aids for hearing loss;
- Limit drinking to 21 or more units of alcohol per week;
- Prevent head trauma where an individual is at high risk;
- Stop smoking;
- Reduce obesity and diabetes by making sure healthy food is available and the ensuring the environment encourages movement; and
- Stay active in midlife and later life.
According to Livingston, these prevention efforts are particularly important in low- and middle-income countries, where the rate of dementia is increasing more quickly than in high-income countries. "People in low- and middle-income countries are now living longer and so are developing dementia more, and they have higher rates of many of the risk factors, including smoking and low education levels," she said. "There is a huge potential for prevention in these countries."
Livingston also noted that the evidence base supporting several of the original risk factors has increased since the original report was published, resulting in tweaks to the Commission's guidance.
For instance, citing a study that found aiming for a systolic blood pressure of 120 mmHg curbed risk for mild cognitive impairment, Livingston said that while the Commission previously "thought under 140 was the target," it now recommends "under 130 to reduce risks of dementia."
Similarly, regarding early-life education, she noted that while it's well-known that education for people under age 11 is linked with reduced dementia risk, it's now thought that education through age 20 can make a meaningful difference.
Livingston also cited new research showing that the use of hearing aids can negate any increased risk of dementia associated with hearing loss. Hearing loss "has both a high relative risk for dementia and is a common problem, so it contributes a significant amount to dementia cases," she said. "This is really something that we can reduce relatively easily by encouraging use of hearing aids. They need to be made more accessible, more comfortable, and more acceptable."
Livingston also noted that, while research into whether diet and sleep are linked to dementia has increased since the 2017 report's publication, they were not included as risk factors in this year's report because the Commission "didn't think the evidence stacked up enough to include these on the list of modifiable risk factors."
Meanwhile, the Commission also included a section in the report on Covid-19, the disease caused by the new coronavirus, noting that people with dementia are particularly at risk for Covid-19 because of their age, comorbidities, and challenges in adhering to social distancing requirements (Hughes, Medscape, 8/3).