Some of the best strategies for reducing your chances of developing dementia are, mercifully, impractical. Don’t grow old; Don’t be a woman; Choose your parents carefully. But although aging remains by far the greatest risk factor, women are at greater risk than men and certain genetic inheritances make dementia more likely or almost inevitable, the latest research suggests that 45% of dementia cases can be prevented – or at least their onset can be delayed.
This is the conclusion of the latest report published on July 31 of the Lancet Commission on Dementia, which brings together leading experts from around the world, and enumerates risk factors which, unlike age, are “modifiable”. It lists 14 of these, adding two from its previous report in 2020: untreated vision loss; and high levels of LDL cholesterol. Despite recent advances in treating some people with Alzheimer’s disease, most of the news seems disappointing about dementia, the most common cause of the condition. Most cases remain incurable and as the world grows older, the number of people suffering from this disease continues to increase. This is a rare ray of hope that the incidence of age-related dementia can actually be reduced.
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 live what has long been considered a healthy life: avoiding tobacco and too much alcohol, and getting plenty of exercise (but avoiding forms of it that involve repeated blows to the head. Injuries include or) bouts of concussion, a list that includes boxing, American football, rugby, and lacrosse).
It also means eating a good diet, defined in a study cited by the Commission as follows: “Eat at least three weekly servings of fruits, vegetables and fish; rarely drink sugar-sweetened beverages; Rarely eat or take out prepared meats such as sausages.” So it’s not surprising that LDL cholesterol has been added to its don’t list. It is also important to exercise the brain: for example, by learning a musical instrument or a foreign language or even crosswords and Sudoku puzzles.
Some physical illnesses do not lead to an increased risk of heart disease or cancer, but have been shown to make dementia more likely. One is untreated hearing loss. The Lancet Commission’s 2020 report concluded that this was the biggest of its 12 risk factors, a finding shared by this latest study. People with hearing loss are almost twice as likely to develop dementia as other people. Widespread availability and use of hearing aids will probably be the single most effective intervention in reducing the incidence of dementia.
It’s also not surprising that vision problems have been added to the latest dementia-risk list. It is not clear why poor hearing and vision should have such an impact on dementia risk. One idea is that they all have the same cause. That hearing aids are very effective in protecting against dementia, however, argues against the theory of deafness. However, diabetes is a risk factor for both vision loss and dementia.
Others speculate that people who struggle to understand what is said to them or to navigate a world blurred by poor vision suffer an increase in debilitating “cognitive load.” It is also possible that these problems disrupt people’s social life and make them lonely. Social isolation and depression are also important risk factors.
against the world
Some 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 received. 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 avoid that is to move on.
Again, the mechanism by which air pollution contributes to dementia risk is disputed. The threat comes from fine particles known as PM2.5 (defined as particles with a diameter of less than 2.5 millionths of a metre), which, if inhaled, can cause stroke, heart disease, There may be an increased risk of lung cancer and respiratory diseases – some of which are themselves risk factors for dementia. But a more direct cardiovascular connection is also possible: The particles can enter the bloodstream and affect the walls of blood vessels, making them less efficient at clearing waste from the brain.
Longitudinal studies of the causes of dementia take years to conduct and are complex to organize. They can be controversial and raise ethical problems (randomized-controlled trials, for example, may only be possible if certain treatable conditions are left untreated). This may make it difficult to reach definite conclusions. For example, many experts wanted sleep disorders to be added to the list of risk factors. In fact, some studies 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 showing that some types of insomnia are actually associated with a reduced risk of developing dementia.
Nevertheless, there is plenty of evidence to show that the risk factors outlined by the Commission are key. For example, in rich Western countries, the incidence rate of dementia has declined by 13% per decade, according to consistent studies over the past 25 years. Gil Livingston, professor of psychiatry of older people at University College London and leader of the Lancet Commission, summarizes the evidence of progress in North America and Europe as “a 25% reduction over the last 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 incidence of age-related dementia is increasing. The overall age-adjusted prevalence rate in Japan doubled from 4.9% in 1985 to 9.6% in 2014. And according to the 2022 China Alzheimer’s Report, the incidence of Alzheimer’s in that country “steadily increased”, making it the fifth highest. The leading cause of death in the country that year.
There is no doubt that the prevalence of dementia is going to increase rapidly over the next decades as humanity ages. All the more reason for dementia risk reduction to become a global policy priority.
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© 2024, The Economist Newspaper Limited. All rights reserved. From The Economist, published under license. Original content can be found at www.economist.com
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