dementia prevalence

Dementia trend shows later onset with fewer years of the disease

  • A large study shows that the falling rates of dementia reflect later onset coupled with shorter time spent with the dementia.

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.

The study involved 5,205 participants from the Framingham Original and Offspring cohorts. Four 5-year periods anchored to different baseline examinations (participants have been examined every four years) were compared. These baseline years are (on average, because participants’ schedules are different): 1978, 1989, 1996, 2006. Participants were those who were aged 60 or older and dementia-free at the start of a time period. There were at least 2000 participants in each time period. In total, there were 371 cases of dementia, and 43% of dementia cases survived more than 5 years after diagnosis.

It was found that the mean age of dementia onset increased by around two years per time period, while age at death increased by around one year. Length of survival after diagnosis decreased over time for everyone, taken as a whole, and also for each gender and education level, taken separately. Survival was almost 6 years in the first time period, and only three years in the last. But the mean age of onset was 80 in the first period, compared to over 86 in the last.

However, the changes haven’t been steady over the 30 years, but rather occurred mostly in those with dementia in 1986–1991 compared to 1977–1983.

Part of the reason for the changes is thought to be because of the reduced risk of stroke (largely because of better blood pressure management), and the better stroke treatments available. Stroke is a major risk factor for dementia. Other reasons might include lower burdens of multiple infections, better education, and better nutrition.

https://www.eurekalert.org/pub_releases/2018-04/uoth-dts042318.php

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One in 4 elderly Australian women have dementia

  • A new estimation technique has raised the dementia rates for Australian women from 20% to 26%.

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.

A new technique based on an ecological method for estimating species population size has been used to estimate dementia rates in the Australian population. The study used 16 years of data from 12,432 Australian women born between 1921 and 1926 who participated in the Women's Health Australia study. Survey data was linked to aged care assessments, the National Death Index, the Pharmaceutical Benefits Scheme, and hospital admissions data to find any instance where the women participating in the study were diagnosed with dementia. This additional data helped overcome the problem of such studies, where participants often just drop out, and the cause isn’t known.

Applying the ecological technique to all this data led to the conclusion that an additional 728 women with dementia had not been identified, increasing the 16 year prevalence from 20.4 to 26.0%. Breaking this down by age, we have:

  • 70-74: 0.3%
  • 75-79: 3.7%
  • 80-84: 16.6%
  • 85+: 31%

https://www.eurekalert.org/pub_releases/2017-03/uoq-oif031617.php

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Rates of new dementia cases may be falling

  • Data from the very long-running Framingham Heart Study adds to evidence that, for those with at least a high school education, the rate of dementia is declining. Improved cardiovascular health and treatment appears to be an important factor in this decline.

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.

Looking at the rate of dementia during four distinct periods in the late 1970s, late 1980s, 1990s, and 2000s, using data from 5205 older adults (60+), the researchers found that there was a progressive decline in the incidence of dementia at a given age, with an average reduction of 20% per decade since the 1970s (22%, 38%, and 44% during the second, third, and fourth epochs, respectively).

There are two important things to note about this finding:

  • the decline occurred only in people with a high school education and above
  • the decline was more pronounced with dementia caused by vascular diseases, such as stroke.

The cumulative risk over five years, adjusted for age and gender, were:

  • 3.6 per 100 persons during the first period (late 1970s and early 1980s)
  • 2.8 per 100 persons during the second period (late 1980s and early 1990s)
  • 2.2 per 100 persons during the third period (late 1990s and early 2000s)
  • 2.0 per 100 persons during the fourth period (late 2000s and early 2010s).

Part of the reason for the decline is put down to the decrease in vascular risk factors other than obesity and diabetes, and better management of cardiovascular diseases and stroke. But this doesn't completely explain the decrease. I would speculate that other reasons might include:

  • increased mental stimulation
  • improvements in lifestyle factors such as diet and exercise
  • better health care for infectious and inflammatory conditions.

The finding is not completely unexpected. Recent epidemiological studies in the U.S., Canada, England, the Netherlands, Sweden and Denmark have all suggested that “a 75- to 85-year-old has a lower risk of having Alzheimer’s today than 15 or 20 years ago.” Which actually cuts to the heart of the issue: individual risk of dementia has gone down (for those taking care of their brain and body), but because more and more people are living longer, the numbers of people with dementia are increasing.

http://www.futurity.org/dementia-rates-decline-1119512-2/

http://www.scientificamerican.com/article/is-dementia-risk-falling/

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How dementia risk varies among ethnic groups

  • A very large U.S. study looking at ethnic differences in dementia risk, has found that African-Americans show the highest rates of dementia, followed by blacks and American Indian/Alaska Natives, then Latinos and whites, with Asian-Americans having the lowest rates.

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:

  • 26.6 cases per 1,000 for blacks
  • 22.2 cases per 1,000 for American Indians/Alaskan Natives
  • 19.6 cases per 1,000 for Latinos and Pacific Islanders
  • 19.3 cases per 1,000 for whites
  • 15.2 cases per 1,000 for Asian Americans.

But this is an annual rate, not particularly useful at a practical level. How do these numbers convert to lifetime risk? Statistical calculations estimate that among those who reach age 65 dementia-free, the following percentages of each ethnicity will develop dementia in the next 25 years:

  • 38% of blacks
  • 35% of American Indians/Alaskan Natives
  • 32% of Latinos
  • 30% of whites
  • 28% of Asian Americans
  • 25% of Pacific Islanders (this is probably the least reliable number, given the small number of Pacific Islanders in the sample).

The study population included 18,778 African-Americans, 4543 American Indians/Alaskan Natives, 21,000 Latinos, 206,490 white Americans, 23,032 Asian-Americans, and 440 Pacific Islanders.

http://www.eurekalert.org/pub_releases/2016-02/kp-lsf021016.php

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[4056] Mayeda, E. Rose, M. Glymour M., Quesenberry C. P., & Whitmer R. A.
(2016).  Inequalities in dementia incidence between six racial and ethnic groups over 14 years.
Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

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Rate of dementia has decreased for African-Americans

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.

The overall standardized annual incidence rate was 3.6% for the 1992 African-American cohort, and 1.4% for the 2001 cohort. For the Yoruba, it was 1.7% and 1.4%, respectively.

It's suggested that one reason for the improvement among African-Americans may be medications for cardiovascular conditions. Although both groups had similar rates of high blood pressure, this was recognized and treated in the American group but not in the Nigerian.

As you can see, African-Americans in the earlier cohort were more than twice as likely as Africans to develop dementia. Their decrease has brought them into line with the African rate.

Although the rate of new cases of dementia decreased, the African-Americans enrolling in 2001 had significantly higher rates of diabetes, hypertension and stroke, but also higher treatment rates, than the African-Americans who enrolled in 1992.

The finding offers hope that treatment can offset the expected increase in dementia resulting from the rise in lifestyle diseases.

http://www.eurekalert.org/pub_releases/2015-08/iu-sn080415.php

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Tracking preclinical Alzheimer's progression

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.

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Over 90% of dementia cases in China are undetected

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.

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Falling in British dementia rate

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

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Diagnosis and prevalence of dementia & MCI — recent reports

August, 2011

Several recent reports point to the need for GPs to be better informed about the initial symptoms of dementia and mild cognitive impairment.

Functional impairment good indicator of mild cognitive impairment

Evaluation of 816 older adults, of whom 229 had no cognitive problems, 394 had a diagnosis of amnestic mild cognitive impairment, and 193 had a diagnosis of mild Alzheimer’s, has revealed that most of those with aMCI (72%) or AD (97%) had trouble with at least one type of function on the Pfeffer Functional Activities Questionnaire. Only 8% of controls had any difficulty. In both impaired groups, those who had the most difficulty functioning also tended to score worse on cognition tests, have smaller hippocampal volumes, and carry the APOe4 gene.

Two of the ten items in the questionnaire were specific in differentiating the control group from the impaired groups. Those items concerned "remembering appointments, family occasions, holidays, and medications” and "assembling tax records, business affairs, or other papers." Only 34% of those with aMCI and 3.6% of those with AD had no difficulty with these items.

The findings suggest that even mild disruptions in daily functioning may be an important clinical indicator of disease.

Early-onset Alzheimer’s poorly diagnosed when initial symptoms aren’t memory related

Post-mortem analysis of 40 people diagnosed  with early-onset Alzheimer’s has revealed that about 38% experienced initial symptoms other than memory problems, such as behavior, vision or language problems and a decline in executive function, or the ability to carry out tasks. Of these, 53% were incorrectly diagnosed when first seen by a doctor, compared to 4% of those who had memory problems. Of those with unusual initial symptoms, 47% were still incorrectly diagnosed at the time of their death.

The mean age at onset was 54.5 years (range 46-60). The average duration of the disease was 11 years, with an average diagnostic delay of 3 years.

GPs misidentify and fail to identify early dementia and MCI

A review of 30 studies involving 15,277 people seen in primary care for cognitive disorders, has found that while GPs managed to identify eight out of ten people with moderate to severe dementia, they only identified 45% of those with early dementia and mild cognitive impairment. Moreover, they were very poor at recording such diagnoses. Thus, though they recognized 45% of the MCI cases, they only recorded 11% of these cases in their medical notes. Although they identified 73% of people with dementia, they made correct annotations in medical records in only 38% of cases.

But the problem is not simply one of failing to diagnose — they were even more likely to misidentify dementia, and this was particularly true for those with depression or hearing problems.

The findings point to the need for more widespread use of simple cognitive screening tests.

Prevalence of dementia & MCI in 'oldest old' women

Data from 1,299 women enrolled in the Women Cognitive Impairment Study of Exceptional Aging suggests that the incidence of dementia almost doubles with every 5 years of age and prevalence rises from approximately 2-3% in those 65 to 75 years to 35% in those 85+.

Among those with mild cognitive impairment, amnestic multiple domain was most common (34%), followed by non-amnestic single domain (29%). Amnestic single domain (affecting only one type of cognitive function, including memory difficulty) affected 22%.

Alzheimer's disease and mixed dementia accounted for nearly 80% of dementia cases, and vascular dementia for 12.1%.

Those with dementia tended to be older, less likely to have completed high school, more likely to have reported depression, a history of stroke, and to have the APOEe4 gene.

The women in the study had an average age of 88.2 years and 27% were older than 90. 41% had clinical cognitive impairment (17.8% with dementia and 23.2% with mild cognitive impairment).

The high prevalence of cognitive impairment in this age group points to the importance of screening for cognitive disorders, particularly among high-risk groups.

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70-year-olds smarter than they used to be

November, 2010

Findings from a large Swedish study are consistent with the hypothesis that more education and better healthcare have produced less cognitive impairment in present-day older adults.

Beginning in 1971, healthy older adults in Gothenburg, Sweden, have been participating in a longitudinal study of their cognitive health. The first H70 study started in 1971 with 381 residents of Gothenburg who were 70 years old; a new one began in 2000 with 551 residents and is still ongoing. For the first cohort (born in 1901-02), low scores on non-memory tests turned out to be a good predictor of dementia; however, these tests were not predictive for the generation born in 1930. Those from the later cohort also performed better in the intelligence tests at age 70 than their predecessors had.

It’s suggested that the higher intelligence is down to the later cohort’s better pre and postnatal care, better nutrition, higher quality education, and better treatment of high blood pressure and cholesterol. And possibly the cognitive demands of modern life.

Nevertheless, the researchers reported that the incidence of dementia at age 75 was little different (5% in the first cohort and 4.4% in the later). However, since a substantially greater proportion of the first cohort were dead by that age (15.7% compared to 4.4% of the 2nd cohort), it seems quite probable that there really was a higher incidence of dementia in the earlier cohort.

The fact that low scores on non-memory cognitive tests were predictive in the first cohort of both dementia and death by age 75 supports this argument.

The fact that low scores on non-memory cognitive tests were not predictive of dementia or death in the later cohort is in keeping with the evidence that higher levels of education help delay dementia. We will need to wait for later findings from this study to see whether that is what is happening.

The findings are not inconsistent with those from a very large U.S. national study that found older adults (70+) are now less likely to be cognitively impaired (see below). It was suggested then also that better healthcare and more education were factors behind this decline in the rate of cognitive impairment.

Previous study:

A new nationally representative study involving 11,000 people shows a downward trend in the rate of cognitive impairment among people aged 70 and older, from 12.2% to 8.7% between 1993 and 2002. It’s speculated that factors behind this decline may be that today’s older people are much likelier to have had more formal education, higher economic status, and better care for risk factors such as high blood pressure, high cholesterol and smoking that can jeopardize their brains. In fact the data suggest that about 40% of the decrease in cognitive impairment over the decade was likely due to the increase in education levels and personal wealth between the two groups of seniors studied at the two time points. The trend is consistent with a dramatic decline in chronic disability among older Americans over the past two decades.

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