How to reduce the risk of developing dementia

Some of the best strategies for reducing the chances of developing dementia are, to put it kindly, impracticable. Don’t grow old; don’t be a woman; choose your parents carefully. But although old age remains by far the biggest risk factor, women are more at risk than men and some genetic inheritances make dementia more likely or even almost inevitable, the latest research suggests that as many as 45% of cases of dementia are preventable—or at least that their onset can be delayed.

That is the conclusion of the latest report, published on July 31st, of the Lancet commission on dementia, which brings together leading experts from around the world, and enumerates risk factors that, unlike age, are “modifiable”. It lists 14 of these, adding two to those in its previous report in 2020: untreated vision loss; and high levels of LDL cholesterol. Most news about dementia seems depressing, despite recent advances in treatments for some of those with Alzheimer’s disease, much the most common cause of the condition. Most cases remain incurable and the numbers with the condition climb inexorably as the world ages. That the age-related incidence of dementia can actually be reduced is a rare beacon of hope.

The modifiable risk factors include smoking, obesity, physical inactivity, high blood pressure, diabetes and drinking too much alcohol (see chart). The best way to reduce the risk of developing dementia is to lead what has long been considered to be a healthy life: avoiding tobacco and too much alcohol and taking plenty of exercise (but avoiding those forms of it that involve repeated blows to the head or bouts of concussion, a list which includes boxing, American football, rugby and lacrosse).

It also means having a good diet, defined in one study cited by the commission as: “Eat at least three weekly servings of all of fruit, vegetables and fish; rarely drink sugar-sweetened drinks; rarely eat prepared meat like sausages or have takeaways.” So it is not surprising that LDL cholesterol has been added to its not-to-do list. It is also important to exercise the brain: by learning a musical instrument or a foreign language, for example—or even by doing crossword and sudoku puzzles.

Some physical ailments do not bring heightened risks of cardiovascular disease or cancer but have been shown to make dementia more likely. One is untreated hearing loss. The Lancet commission’s report from 2020 concluded this was the biggest of its 12 risk factors, a conclusion shared by this latest study. People with hearing loss are about twice as likely as others to develop dementia. The wider availability and use of hearing aids would probably be the single intervention most effective in reducing the incidence of dementia.

It is also not surprising that eyesight problems have been added to the latest dementia-risks list. It is unclear why impaired hearing and vision should have such an impact on the risk of dementia. One idea is that they all have a common cause. That hearing aids are very effective in protecting against dementia, however, argues against that theory for deafness. Diabetes, however, is a risk factor for both failing eyesight and dementia.

Others speculate that people straining to understand what is said to them or to navigate a world made hazy by poor eyesight suffer a debilitating increased “cognitive load”. It may also be that these problems inhibit people’s social lives and make them lonelier. Social isolation and depression are also important risk factors.

Against the world

Some of the modifiable risk factors are, in fact, far beyond any individual’s control. For example, it makes a big difference how many years of education someone has had. Broadly speaking, the higher the level of educational attainment, the lower the risk of dementia. Polluted air is another risk factor. And the only guaranteed way to escape that is to move.

Again, the mechanism by which air pollution contributes to dementia risk is disputed. The danger comes from fine particles known as PM2.5 (defined as those measuring less than 2.5 millionths of a metre in diameter) that, if inhaled, can increase the risk of strokes, heart disease, lung cancer and respiratory diseases—some of which are themselves risk factors for dementia. But a more direct cardiovascular link is also possible: the particles could enter the bloodstream and affect the walls of blood vessels, making them less efficient in clearing the brain of waste.

Longitudinal studies into the causes of dementia take years to run and are complex to organise. They can be controversial and raise ethical problems (randomised-controlled trials, for example, might be possible only if some curable conditions were left untreated). That can make definitive conclusions hard to reach. Many experts, for example, had wanted sleeping disorders added to the list of risk factors. Some studies do, in fact, suggest that poor sleep patterns in middle age may contribute to a higher risk of dementia in later life. But the evidence is mixed, with other studies suggesting that some sorts of insomnia are actually associated with a diminished risk of developing dementia.

Nevertheless, there is plenty of evidence to show that the risk factors outlined by the commission are salient. In rich Western countries, for example, the incidence rate of dementia has declined by 13% per decade over the past 25 years, consistently across studies. Gill Livingston, a professor in the psychiatry of older people at University College London and leader of the Lancet commission, has summed up the evidence of progress in North America and Europe as “a 25% decrease in the past 20 years”. Such rapid and significant change can only be the result of changes in modifiable risk factors.

Despite the upbeat tone of the commission’s report, in some countries, such as China and Japan, the age-related incidence of dementia is climbing. In Japan the overall age-adjusted prevalence rate doubled from 4.9% in 1985 to 9.6% in 2014. And according to the China Alzheimer Report of 2022, the incidence of Alzheimer’s in that country had “steadily increased”, making it the fifth-most important cause of death in the country in that year.

Nobody doubts that the prevalence of dementia is going to climb fast in the next decades as humanity ages. All the more reason for dementia-risk reduction to become a global policy priority. ■