Contrary to popular estimates about the future of Alzheimer's, fewer people are getting dementia than expected, suggesting that dementia is on the decline.
For some time, we’ve thought that the number of Alzheimer’s disease patients would triple by 2050, as the baby boomers grow old. But something wonderful is happening instead: Fewer people are getting the disease than expected.
In a study of nearly 50,000 seniors over 25 years, published in the leading journal for neurologists, Neurology, researchers pooled data from the United States and five countries. They found that the percentage of the population with the disease adjusted for age has dropped in each of the past three decades. Overall, the portion that developed dementia was 8.6 percent.
The authors noted that in China and Nigeria, the percentages have stayed stable or increased, and the evidence is mixed for minorities in the United States.
The number of people with the disease is still rising as populations age, but the better trends suggest that more effective treatment for heart disease and other lifestyle improvements are helping.
Fewer than expected
Some six million American seniors do have dementia. If the rate hadn’t dropped, that figure was expected to be more than 6 million.
Researchers at the University of Michigan came to this conclusion when they analyzed data on more than 10,500 participants in a government survey of seniors in 2000 and 2012. They reported their results in JAMA Internal Medicine.
Other studies have reached the same conclusion about a decline in dementia; the Neurology study included data from the long-running Framingham study, which found a drop in every decade between 1977 and 2008.
Why would dementia decline?
Studies like these don’t explain the biology in any one person. They show trends. Education can help protect people from dementia, since it literally builds more machinery in the brain that can fill in when parts become affected by the disease. In the JAMA study, the average person in 2012 group had, on average, about one year more education than the average person in 2000. But this explained only part of the decline, the University of Michigan team reported.
In fact, the steady increase in the average weight, while dangerous for other reasons, is associated with lower dementia numbers. A separate 2015 study tracking two million people over two decades, reported in the prestigious journal The Lancet, concluded that the incidence of dementia fell as BMI (body mass index) rose. People who were very obese in mid-life had a 29 percent lower risk of dementia 15 years later than people of a healthy weight. On the other hand, being underweight at midlife made your risk 34 percent higher than if you had a healthy weight.
The dangers of obesity
Don’t let this make you think obesity is healthy, however; it is associated with a greater risk of dying young, sleep apnea, depression and other mental illness, pain, and various cancers, including endometrial, breast, colon, kidney, gallbladder, and liver cancer. The Lancet study also showed the usual link between dying prematurely and being overweight or obese. Even if extra weight protected you from dementia, you might not live long enough to enjoy your mental clarity.
No one knows if obesity might protect us from dementia. Research is underway that could lead to another happy result: harnessing that protective effect with treatment.
So if you’re overweight and have a close family member with dementia should you make a priority of losing weight? Most likely, yes, but it depends how you go about it. A crash diet won’t be good for you, and will very likely set you up to regain even more weight.
Your best move is to make sure you have a healthy lifestyle overall: eat healthily, exercise several days a week (if not every day), get enough sleep, and make sure you have healthy pleasures in your life and effective ways to calm down when you’re stressed. If you are obese, there are a variety of ways doctors can help you. Know your options and talk to your doctor.
December 18, 2020
Christopher Nystuen, MD, MBA