More Evidence that Dementia Case Numbers Are Falling

Numerous studies have reported a dip in dementia incidence in the developed world. When did this trend begin? In the September 5 JAMA Neurology, researchers led by Carol Derby at Albert Einstein College of Medicine in New York help address this. The researchers analyzed birth cohort data from the Einstein Aging Study, which enrolls cognitively healthy older adults living in the Bronx. Surprisingly, people born after 1928 were 85 percent less likely to develop dementia than those born before that year. The reason for such a stark drop in incidence is unclear. Neither better education nor improved cardiovascular health accounted for the effect.

A growing number of studies have reported a drop in dementia incidence in the U.S. and Europe over the last two or three decades (e.g., Feb 2016 newsApr 2016 newsNov 2016 news). Researchers have speculated that this may be due to better public health, particularly cardiovascular health (May 2013 newsJul 2014 conference news). The finding is not uniform, however, with a handful of studies reporting higher dementia incidence that may be due to greater recognition of the disease or a larger number of people reaching old age (Mar 2017 newsMay 2017 newsAbdulrahman 2014). 

“Changes in diet, especially for the mother during pregnancy, may be a crucial factor,” agreed Walter Rocca at the Mayo Clinic in Rochester, Minnesota. In addition, Rocca pointed out that people born in 1929 or after would have been teenagers or younger at the end of World War II, and thus their developing brains may have particularly reaped the benefits of the societal and medical changes that occurred at that time (see full comment below).

While previous epidemiological studies did not specifically examine birth years, those older findings are roughly congruent with the Einstein Aging Study data, reporting the greatest drop in dementia cases after 1990, the authors noted. People born after 1929 would have entered their 60s in that decade. Most cases of late-onset dementia occur after age 60. The Rotterdam Study found a 25 percent decrease in dementia incidence in the 1990s, while the Framingham Heart Study recently reported that incidence dropped starting in the late 1980s and continued to decline into the 2010s (Schrijvers et al., 2012Satizabal et al., 2016).