Hearing loss
The researchers assessed how much each risk factor contributes to dementia, expressed as the population-attributable fraction (PAF). Hearing loss had the greatest effect, accounting for an estimated 8.2% of dementia cases. This was followed by lower education levels in young people (7.1%) and smoking (5.2%).
Dr. Livingston noted that the evidence that hearing loss is one of the most important risk factors for dementia is very strong. New studies show that correcting hearing loss with hearing aids negates any increased risk.
Hearing loss “has both a high relative risk for dementia and is a common problem, so it contributes a significant amount to dementia cases. 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,” she said.
“This could make a huge difference in reducing dementia cases in the future,” Dr. Livingston added.
Other risk factors for which the evidence base has strengthened since the 2017 report include systolic blood pressure, social interaction, and early-life education.
Dr. Livingston noted that the SPRINT MIND trial showed that aiming for a target systolic blood pressure of 120 mm Hg reduced risk for future mild cognitive impairment. “Before, we thought under 140 was the target, but now are recommending under 130 to reduce risks of dementia,” she said.
Evidence on social interaction “has been very consistent, and we now have more certainty on this. It is now well established that increased social interaction in midlife reduces dementia in late life,” said Dr. Livingston.
On the benefits of education in the young, she noted that it has been known for some time that education for individuals younger than 11 years is important in reducing later-life dementia. However, it is now thought that education to the age of 20 also makes a difference.
“While keeping the brain active in later years has some positive effects, increasing brain activity in young people seems to be more important. This is probably because of the better plasticity of the brain in the young,” she said.
Sleep and diet
Two risk factors that have not made it onto the list are diet and sleep. “While there has also been a lot more data published on nutrition and sleep with regard to dementia in the last few years, we didn’t think the evidence stacked up enough to include these on the list of modifiable risk factors,” Dr. Livingston said.
The report cites studies that suggest that both more sleep and less sleep are associated with increased risk for dementia, which the authors thought did not make “biological sense.” In addition, other underlying factors involved in sleep, such as depression, apathy, and different sleep patterns, may be symptoms of early dementia.
More data have been published on diet and dementia, “but there isn’t any individual vitamin deficit that is associated with the condition. The evidence is quite clear on that,” Dr. Livingston said. “Global diets, such as the Mediterranean or Nordic diets, can probably make a difference, but there doesn’t seem to be any one particular element that is needed,” she noted.
“We just recommend to eat a healthy diet and stay a healthy weight. Diet is very connected to economic circumstances and so very difficult to separate out as a risk factor. We do think it is linked, but we are not convinced enough to put it in the model,” she added.
Among other key information that has become available since 2017, Dr. Livingston highlighted new data showing that dementia is more common in less privileged populations, including Black and minority ethnic groups and low- and middle-income countries.
Although dementia was traditionally considered a disease of high-income countries, that has now been shown not to be the case. “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. There is a huge potential for prevention in these countries,” said Dr. Livingston.
She also highlighted new evidence showing that patients with dementia do not do well when admitted to the hospital. “So we need to do more to keep them well at home,” she said.