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Dementia Prevalence Is Falling, So Why Is the Alzheimer's Death Rate Rising?

Ben Hanowell
By Ben HanowellAugust 14, 2017

The Population Reference Bureau says the share of older adults with dementia in the U.S. dropped 24% from 2000-2012. Yet the Centers for Disease Control says Alzheimer’s deaths rose 55% from 1999-2014, and that the number of people with Alzheimer’s will quadruple by 2050. How can all three numbers be true?

Don’t give up on the experts. We explain why this all makes perfect sense.

The Ways Dementia Disease Burden Can Rise and Fall

To understand Alzheimer’s disease and dementia statistics, you need to understand the ways that the number of people with a disease can rise or fall. We describe each one and how it could explain current trends.

If people start surviving longer with dementia, numbers will rise.

If better treatment helps people survive longer with Alzheimer’s, then more people will be counted with the disease. On the other hand, if something causes Alzheimer’s survivorship to fall, people with the disease will die earlier and numbers will drop over time. A recent review of dementia studies since 1980 suggests dementia patients are indeed surviving longer and longer.

A recent review of dementia studies since 1980 suggests dementia patients are surviving longer and longer, causing the population affected to rise.

If more people survive other medical conditions, more will live long enough to get dementia.

Degenerative diseases like Alzheimer’s, which affect mainly older people, have become major killers over time because fewer people die earlier in life from deadly infectious diseases like measles or smallpox. Something similar has happened more recently: medical innovations increase survival among heart disease and stroke patients. That leaves more people living to the oldest ages, when the risk of dementia rises dramatically.

Because of improved survival from heart disease and stroke, more people survive long enough to be at greater risk for dementia.

If more people who have dementia get diagnosed, the count will rise.

You can’t be counted as having a disease if that disease has not been diagnosed by a knowledgeable medical professional. Disease definitions change over time as medical understanding evolves and diagnosis methods improve. Patients can also change their behaviors in ways that affect the likelihood of diagnosis.

According to the CDC, improved diagnosis could be one reason for rising Alzheimer’s disease mortality. Dr. Kenneth Langa, Professor of Medicine at University of Michigan, also notes:

[The] more important explanation [for rising Alzheimer’s mortality] is that the coding of AD [Alzheimer’s disease] / dementia on death certificates is changing over time; in other words, given the same level of cognitive impairment now compared to 20 years ago, a person is more likely to have their AD / dementia coded on their death certificate because of greater recognition of the condition by patients and health care providers. So many researchers view the increase in AD mortality rate, as partly (perhaps mainly) due to a change in coding practices rather than a “real” change in the number of people dying with AD.

Dr. Kenneth Langa, Cyrus Sturgis Professor of Medicine at University of Michigan

Improved Alzheimer’s diagnosis both before and after death has increased both the number of people counted as affected, and the number of deaths attributed to Alzheimer’s.

If the factors that cause Alzheimer’s become more prevalent, Alzheimer’s can become more prevalent.

Many assume that if a disease is becoming more common, it must be because whatever external factors that cause it are becoming a bigger problem. But remember all the other possible explanations before you jump to conclusions.

Besides, if anything, dementia risk factors have diminished over time. According to the Population Reference Bureau, more people reach higher levels of education now, which could directly affect brain development in a way that protects against dementia.

Another protection against dementia risk is more aggressive treatment of risks for heart disease and diabetes. Having heart disease and diabetes is associated with higher risk of Alzheimer’s. Protecting against one could protect against the other.

Improved education and more aggressive treatment of heart disease and diabetes risk factors may reduce the number of dementia cases over time.

Now that you understand how the number of people with dementia can rise and fall, let’s get back to the original questions.

Why Dementia Prevalence Can Fall But Alzheimer’s Numbers Will Quadruple

The prevalence of a disease is the share of the population in a particular place and time who has that disease. Disease prevalence is not the number of people who have that disease.

Now that you know what prevalence is, here’s the answer to the question, step by step:

  1. In the year 2000, dementia prevalence among older adults in the United States was about 12%. There were about 31.2 million older adults. That means about 3.6 million people had dementia.
  2. Dementia prevalence in 2012 was only about 9%, but the population of older adults had climbed to about 43.1 million. So even though dementia prevalence declined, the number of people with dementia grew to 3.8 million.
  3. The number of people 65 and older will double by 2050.The number 85 and older will more than triple. Older people are the main risk group for Alzheimer’s, thus for Alzheimer’s death.
  4. Add in greater survival rates among dementia patients and better diagnosis, and it seems more plausible that the number of people with Alzheimer’s could quadruple even though the prevalence of dementia is dropping.

Why Dementia Prevalence Can Fall While Alzheimer’s Death Rate Rises

Mortality (or the death rate) is the number of deaths that occur out of the average number of people in a population. Here’s how Alzheimer’s mortality can rise even as dementia prevalence falls.

  • Older people today are less likely to get dementia than older people in previous years.
  • Younger people today are also less likely to get dementia than younger people in previous years.
  • Still, you’re more likely to get dementia if you’re old and the older population is growing faster than the younger population.
  • So even though the risk of getting dementia is dropping in each age group, the age groups more likely to get dementia are growing in number at an unprecedented rate.
  • Due to improved diagnosis rates, better cause-of-death determination, better dementia prognosis and better treatment of other diseases, the number of people that die from Alzheimer’s is rising at the same time the older population is growing.

The Takeaway

We hope this explainer helps you better understand dementia and Alzheimer’s statistics. If you remember just four things, here they are:

  1. The number of people who have dementia can rise for a variety of reasons, not just because the causes of that disease are becoming a bigger problem.
  2. It’s totally possible for dementia prevalence to drop even as Alzheimer’s mortality rises.
  3. The more sensational a headline about dementia or Alzheimer’s, the more you should be skeptical.
  4. The CDC, the Census Bureau and epidemiologists aren’t just making the numbers up as they go along.
Ben Hanowell

Ben Hanowell

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