A large study using data from the famous Framingham Heart Study has compared changes in dementia onset over the last three decades. The study found that over time the age of onset has increased while the length of time spent with dementia has decreased.
In Australia, it has beens estimated that 9% of people aged over 65, and 30% of those aged over 85 have dementia. However, these estimates are largely based on older data from other countries, or small local samples.
As we all know, people are living longer and obesity is at appalling levels. For both these (completely separate!) reasons, we expect to see growing rates of dementia. A new analysis using data from the long-running Framingham Heart Study offers some hope to individuals, however.
A study involving 14 years of health records from more than 274,000 Northern Californians has assessed the relative dementia risk of six different ethnicities.
The average annual rate of dementia was:
A long-running study comparing African-Americans and Nigerians has found the incidence of dementia has fallen significantly over two decades among the African-Americans, but remained the same for the Nigerians (for whom it was lower anyway).
The study enrolled two cohorts, one in 1992 and one in 2001, who were evaluated every 2–3 years until 2009. The 1992 cohort included 1440 older African-Americans (70+) and 1774 Nigerian Yoruba; the 2001 cohort included 1835 African-Americans and 1895 Yoruba. None of the participants had dementia at study beginning.
New research supports the classification system for preclinical Alzheimer’s proposed two years ago. The classification system divides preclinical Alzheimer's into three stages:
Stage 1: Levels of amyloid beta begin to decrease in the spinal fluid. This indicates that the substance is beginning to form plaques in the brain.
Stage 2: Levels of tau protein start to increase in the spinal fluid, indicating that brain cells are beginning to die. Amyloid beta levels are still abnormal and may continue to fall.
A survey of 7,072 older adults in six provinces across China, with one rural and one urban community in each province, has identified 359 older adults with dementia and 328 with depression. There were only 26 participants who had doctor-diagnosed dementia reported and 26 who had doctor-diagnosed depression. Overall, 93% of dementia cases and 93% of depression were not detected.
Undetected dementia was strongly associated with low socioeconomic status such as a low educational and occupational class, and living in a rural area.
A survey of 7796 older adults (65+) living in three geographic areas in England has allowed us to compare dementia rates over time, with an identical survey having been taken between 1989 and 1994. The overall prevalence of dementia fell significantly, from 8.3% to 6.5%.
The finding provides further evidence that a cohort effect exists in dementia prevalence.
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2813%2961570-6/fulltext
Most older adults do not suffer cognitive impairment. Around 30-40% of adults over 65 have the type of cognitive loss we regard as a normal consequence of age — a measurable (but slight) decline on memory tests; a feeling that you're not quite as sharp or as good at remembering, as you used to be (age-related cognitive impairment). Around 10% of adults over 65 develop mild cognitive impairment (MCI), which does impact everyday living, and is a precursor of Alzheimer's.
There are significant differences in prevalence as a function of age. For example, in the U.S., a large sample found MCI in 9% of those aged 70 to 79 and nearly 18% of those 80 to 89. Prevalence decreased with years of education: 25% in those with up to eight years of education, 14% in those with nine to 12 years, 9% in those with 13 to 16 years, and 8.5% in those with greater than 16 years.
Large-scale population surveys of mild cognitive impairment in the elderly have produced large differences in national levels, ranging from 10% to 26%.
Although women may decline at a faster rate than men, prevalence of decline may be greater among men. For example, a large Dutch survey of those aged 85 and older found more women than men had good memory (41% vs 29%) and mental speed (33% vs 28%), despite the fact that more women than men had a limited education.
However, severe memory problems in the elderly have become more rare. The main reasons seem to be better physical fitness (partly due to better healthcare), higher levels of education, and greater personal wealth.
Another finding from the Religious Orders Study. It seems that mild cognitive impairment is often the earliest clinical manifestation of Alzheimer’s or vascular dementia. By studying the brains of study participants after death, researchers could ascertain that, of the 37 individuals with mild cognitive impairment, 23 met pathologic criteria for Alzheimer's disease, and 12 had cerebral infarcts (5 had both). Only 9 did not have either pathology. The researchers conclude that even mild loss of cognitive function in older people should not, therefore, be viewed as normal, but as an indication of a disease process.
Bennett, D. A., Schneider, J. A., Bienias, J. L., Evans, D. A., & Wilson, R. S. (2005). Mild cognitive impairment is related to Alzheimer disease pathology and cerebral infarctions. Neurology, 64(5), 834-841. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/15753419
http://www.eurekalert.org/pub_releases/2005-03/rpsl-mop022805.php
A large-scale epidemiological study in the Netherlands has found an incidence of frontotemporal dementia that equates to a population level of 1.1 per 100,000. The prevalence was highest among those ages 60 to 69, at 9.4 per 100,000. The prevalence among people ages 45 to 64 was estimated to be 6.7 per 100,000. Symptoms began after age 65 in 22% of patients. Whites accounted for 99% of all cases despite an ample nonwhite population. A family history of dementia was present in 43% of patients.
Ravid, R., Niermeijer, M. F., Verheij, F., Kremer, H. P., Scheltens, P., van Duijn, C. M., … Kamphorst, W. (2003). Frontotemporal dementia in The Netherlands: patient characteristics and prevalence estimates from a population-based study. Brain, 126(9), 2016-2022. Retrieved from http://brain.oxfordjournals.org/cgi/content/abstract/126/9/2016
In the first population-based study of cognitive impairment in the United States, nearly one in four older African Americans in Indianapolis were found to have measurable cognitive problems (short of dementia or Alzheimer's). The prevalence of cognitive impairment grew significantly with age, with rates increasing by about 10 percent for every 10 years of age after age 65. Of those aged 85 and older, 38% had some degree of cognitive impairment. Surveys in other countries (which cannot be directly compared due to differences in methodology, diagnostic criteria, etc) have reported results ranging from 10.7% in Italy to 26.6% in Finland.
Musick, B., Hall, K. S., Hui, S. L., Hendrie, H. C., Unverzagt, F. W., Gao, S., … Evans, R. (2001). Prevalence of cognitive impairment: Data from the Indianapolis Study of Health and Aging. Neurology, 57(9), 1655-1662. Retrieved from http://www.neurology.org/cgi/content/abstract/57/9/1655
http://www.eurekalert.org/pub_releases/2001-11/nioa-cih110701.php
http://www.eurekalert.org/pub_releases/2001-11/aaon-mla110501.php
Researchers from Leiden University tested the mental functioning of 599 Dutch men and women aged 85 years. Good mental speed on word and number recognition tests was found in 33% of the women and 28% of the men. Forty one per cent of the women and 29% of the men had a good memory. This despite the fact that significantly more of the women had limited formal education compared to the men (not surprising given the time in which they grew up). The authors suggested that biological differences - such as the relative absence of cardiovascular disease in elderly women compared with men of the same age - could account for these sex differences in mental decline.
van Exel, E., Gussekloo, J., de Craen, A. J. M., van der Wiel, B.-, Houx, P., Knook, D. L., & Westendorp, R. G. J. (2001). Cognitive function in the oldest old: women perform better than men. Journal of Neurology, Neurosurgery & Psychiatry, 71(1), 29-32. Retrieved from http://jnnp.bmj.com/content/71/1/29.abstract
http://www.eurekalert.org/pub_releases/2001-06/BSJ-Ewhb-1706101.php
Severe memory problems in older adults have become more rare, probably because of better treatments for dementia, depression and strokes. Researchers from the University of Michigan interviewed more than 10,000 people ages 70 and older from 1993 to 1998. People tested in 1998 did significantly better on the memory tests than those tested earlier. In 1998 less than 4% of those 70 and older showed severe memory problems, and only 8% of those 85 and older. Surprisingly, the greatest improvement was seen among those in their 80s and those with less than a high school education. The decline in memory problems is believed to be associated with the improvement in physical fitness seen among the elderly. It is speculated that the increase in number of women on hormone replacement therapy may also play a part.
Freedman, V. A., Aykan, H., & Martin, L. G. (2001). Aggregate Changes in Severe Cognitive Impairment Among Older Americans. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 56(2), S100 -S111 - S100 -S111. Retrieved from http://psychsocgerontology.oxfordjournals.org/content/56/2/S100.abstract