The Incidence of Dementia Is Declining...

...but prevalence is not.  At least in industrialized countries like Denmark.

Something interesting about Denmark is their very comprehensive database for tracking health conditions of all Danish citizens from birth.  Among other uses, the data in the databases can be used as a basis for many different types of longitudinal studies.  For example, a comparison was made between immunizations and the occurrence of autism in children that encompassed every Danish child.  The study found that fewer immunized children developed autism than those not immunized, although the correlation was within the margin of error.

This week's journal, Alzheimer's and Dementia, published an interesting article in which researchers, mostly from the University of Copenhagen, delved the national database to find trends in the incidence of dementia.  What they found was consistent with what we've seen in the US -- that the incidence of dementia has been declining for several years.  What's good about this study is that the data is more reliable and comprehensive than data used in other studies, and provides a little more detail.

The second edition of Beating the Dementia Monster is still a ways off, but we will discuss this phenomenon there.

Now, when we say that the incidence of dementia has declined, that does not mean that its prevalence has declined.  Incidence corresponds to the probability that someone will develop dementia, prevalence speaks to the total number of people who have developed the syndrome.  So while people may develop dementia at a slower rate, a population that is increasingly older will have more people with dementia.

The study filled in some blanks for me.  It found that the incidence of dementia increased an average of 9% annually from 1996 to 2003.  That's pretty steep.  But in 2003 the rate of increase leveled off, and then declined 2% annually until 2015.

Why?

It is believed that people made many lifestyle changes as part of a campaign within the industrialized countries to control cardiovascular disease.  Lifestyle improvements along with drugs for control of blood pressure and cholesterol appear to be responsible for the decline.

The researchers looked at other studies in Asia and North America (notably the Framingham Heart Study), and found that they too measured declines in the incidence of dementia.  However, several noted that, while the overall incidence of dementia may have declined, the incidence of Alzheimer's disease did not.  This strongly suggests that it is vascular dementia that is being influenced by improving cardiovascular health and maybe not Alzheimer's disease.

Nevertheless, lifestyle changes with respect to physical exercise, diet, stress management, sleep, and social connection can beat back the advance of cognitive decline from Alzheimer's disease.