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Some facts and
figures
Why did my father
get Alzheimer’s disease? He was such a good man.
It is estimated that there are currently about 18 million
people worldwide with Alzheimer’s disease. This figure is projected to nearly
double by 2025 to
34 million. Much of this increase will be in the
developing countries, and will be due to the ageing population. Currently,
more than 50% of people with Alzheimer’s disease live in developing countries
and by 2025, this will be over 70%.
Effect of age on
risk of Alzheimer’s disease
Alzheimer’s disease can occur at any age, even as young as
40 years, but its occurrence is much more common as the years go by. In fact,
the rate of occurrence of the disease increases exponentially with age, which
means that it occurs very rarely among those 40-50 years old, increases between
60 and 65 years, and is very common over 80 years. In November 2000, the
National Institute on Aging (USA) estimated that up to 50% of Americans aged
85 years or more may have Alzheimer’s disease. Combining the results of
several studies, the following rates of occurrence of Alzheimer’s disease are
estimated in the general population in the West:
Since the risk of getting the disease increases with age,
the number of patients with the illness to be found in any community will
depend on the proportion of older people in the group. Traditionally, the
developed countries had large proportions of elderly people, and so they had
very many cases of Alzheimer’s disease in the community at one time. However,
the developing countries are now undergoing a demographic transition so that
more and more persons are surviving to an old age. For example in India,
the 1991 census revealed that 70 million people were over 60 years. This
number increased in 2001 to about 77 million, or 7.6% of the population.
Similar demographic changes are occurring in other Member Countries of the
SEA Region.
In Sri Lanka,
the life expectancy is 74.1 (with 9.6% of the population being over 60
years), which is the highest in the Region, followed by Thailand
(life expectancy 70, with 8.7% of the population over 60 years). With this
increased number of elderly people, there will be many cases of Alzheimer’s
disease. Thus, the time has come to discuss issues related to Alzheimer’s
disease in the Member Countries of the Region.
Urban/rural
differences
Recent research in India
and Africa suggests that the risk of Alzheimer’s
disease was possibly higher for urban as compared to rural areas. This has
raised several important issues for research: What is the deciding factor? Is
it increased life expectancy? Is it lifestyle? Is it diet?
Gender differences
It is generally believed that men and women are equally at
risk of Alzheimer’s disease. However, in developed countries, it is commonly
observed that more women than men patients are to be found in old age homes
and special care facilities. This is a reflection of the higher longevity of
women as compared to men, and since this is a disease which strikes older
people, there are more women patients than men. There is no evidence that
women are at an increased risk of the disease than men, when the age factor
is correlated in existing data. Also, women are better able to care for male
patients than men are able to care for female patients. Thus, a woman with
Alzheimer’s disease has a higher chance of being put into an institution
because of her husband’s inability to take care of her. However, a man with
Alzheimer’s disease has a higher chance of his wife taking care of him at
home. Thus, a greater number of women patients are found in institutions.
Education
Some research studies have suggested that those with
higher education are at a lower risk for Alzheimer’s disease than those with
less education. Although this has been repeatedly demonstrated in several
projects, the reason for this association is unknown.
East-West
differences
Studies done in South India, Mumbai and the northern state
of Haryana in India have reported very low rates of
occurrence of Alzheimer’s disease in those at 65 years of age or older,
ranging from about 1% in rural north-India (the lowest reported from anywhere
in the world where Alzheimer’s disease has been studied systematically) to
2.7 in urban Chennai.
Studies from China
and Taiwan
have also shown a lower risk of Alzheimer’s disease as compared to western
countries. The low rates of occurrence of Alzheimer’s
disease in the eastern countries is in striking contrast to data from
the western countries.
Community-based studies are of particular interest when
they look at populations similar in origin but subject to relocation. Some
Japanese reports are important in this respect. Two recent investigations in
the rural areas of Japan
revealed that Alzheimer’s disease occurred in about 3.5% of individuals aged
65 or more. Reported research in 1996 among older Japanese Americans living
in Washington and in Hawaii
revealed that the number of Alzheimer’s disease cases was much higher than
that estimated in Japan
and closely resembled the findings for North America
and Europe.
Similarly, research studies comparing
the Yorba’s living in Ibadan,
Nigeria, and
African-Americans living in Indianapolis, USA,
are also of interest as the groups share an ethnic background but live in
widely different environments. In the Ibadan group, the proportion of
Alzheimer’s disease cases was a low 1.4% (similar to rates in India),
while the rate for Alzheimer’s disease among the African-Americans was
estimated at 6.2%.
From the available evidence, it would appear that the
number of cases of Alzheimer’s disease in Asia, and
particularly in India
and Africa, is lower than that reported from studies
in developed countries. This raises a major question - why?
There are several possible reasons. Perhaps physicians do
not diagnose Alzheimer’s disease but use non-specific terms such as senility.
Other postulates refer to the socioeconomic realities and the lack of
awareness of Alzheimer’s disease in the populations studied. It is likely
that there is a low survival rate after the onset of the disease. Poor access
to technologically-advanced health care may especially hasten the demise of
patients, resulting in lower estimates of number of cases. Some have also
speculated that the traditional attitude towards the elderly being one of
respect, "family members will not force medical care or even food on an
older relative who takes to his bed and refuses to eat" - a contributory
factor in low survival.
It is possible that there is a lower occurrence of
underlying risk factors (or the concomitant presence of protective factors)
in the populations surveyed. For example, there is some evidence that the
occurrence of a specific gene, Apolipoprotein EÎ4,
which is a known risk factor in Alzheimer’s disease, is lower in the Indian
population than elsewhere. This theory seems to be corroborated by the
preliminary results from a genetic study of patients and comparable subjects
without Alzheimer’s disease, which indicated a lower occurrence of Apolipoprotein EÎ4 gene in North India
compared to the west. Additionally, gene-environment interactions have also
been postulated as responsible factors for the lower number of cases in
eastern countries.
Risk factors for
Alzheimer’s disease
Millions of dollars have been spent worldwide in trying to
determine why certain people get Alzheimer’s disease. However, only two established
risk factors, i.e., factors that increase a person’s risk of getting
Alzheimer’s disease have been discovered.
The first identified risk factor is increasing age. As
already discussed, the risk of getting Alzheimer’s disease increases
exponentially with age. But this does not mean that everyone living to a
certain age or beyond will get Alzheimer’s disease.
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What are my
risks, Doctor?
There is increasing awareness of a genetic
predisposition to Alzheimer’s disease, i.e., children of patients are afraid
that they may inherit the disease. The risk of inheritance on a genetic
basis is extremely small.
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The other identified risk factor is a genetic
predisposition.
Since Alzheimer’s disease is common among older people,
even if many members in a family are affected by Alzheimer’s disease, it does
not necessarily mean that the disease is being transmitted within the family
on a purely genetic basis.
To date, three genetic defects considered as
"causative genes" have been identified in patients of Alzheimer’s
disease. In other words, people inheriting these genes from their parents
will get the disease. One defect each is situated on chromosome 14,
chromosome 19 and on chromosome 21. There may be other possible genetic
defects, as yet unidentified, in patients of Alzheimer’s disease. These
genetic defects manifest themselves by aggregation of multiple cases of
Alzheimer’s disease within families affecting multiple generations. However,
it must be emphasized that the proportion of all cases of Alzheimer’s disease
which are inherited on a genetic basis is less than 1-2% of all known cases
of Alzheimer’s disease.
Another mechanism of genetic effect is the inheritance of
a "susceptibility gene". The best known susceptibility gene
identified by medical research is the Apolipoprotein
E Î4 gene. Inheriting this gene does not mean that the person will get
Alzheimer’s disease; there are numerous patients who have these genes and do
not get Alzheimer’s disease, while there are numerous patients who do not
have these genes and yet get Alzheimer’s disease. Researchers believe that
external factors must interact with this susceptibility gene to precipitate
Alzheimer’s disease. This interaction is referred to as
"gene-environment interaction" by medical researchers. The external
factors are still unknown. However, since Apolipoprotein
E Î4 is known to affect cholesterol metabolism, research in India
and Nigeria
has suggested that a high-fat diet, as is typical in western countries, may
be one of the factors which interacts with Apolipoprotein
E Î4 gene to increase the risk of Alzheimer’s disease in the West. This is a
subject of intense research and remains to be proved.
At the current stage of knowledge, it is impossible to
predict who will get Alzheimer’s disease. It can strike anyone irrespective
of gender, caste, creed, culture or socioeconomic status
Other factors
linked to Alzheimer’s disease
Increasingly, reports suggest that the use of certain
drugs has been associated with reduction of risk of Alzheimer’s disease. These
include hormones such as the oestrogens in
menopausal women, non-steroidal anti-inflammatory drugs, antioxidants such as
vitamin E, vitamin B and lipid-lowering agents.
Many other factors have been implicated such as viral
infection, aluminium poisoning, as also family
history of other genetic defects, and the risk to children born to elderly
mothers. However, none of these factors has been proven to increase the risk
of Alzheimer’s disease.
Cost of
Alzheimer’s disease
Alzheimer’s disease is a chronic and progressive neurodegenerative disorder. It is, therefore, to be
expected that the cost of caring for these patients is enormous. Keeping in
mind the 1991 levels and future generations of patients of Alzheimer’s
disease, a researcher in the US
estimated that in the year 2000, the direct and total national cost to the US
was approximately US$ 536 billion and US$ 1.75 trillion respectively. These
are minimum estimates of the long-term dollar losses to the US
economy at 1991 levels caused by Alzheimer’s disease. Similar detailed
costing is not available in respect of other countries.
Besides the monetary cost, many spouses, relatives and
friends take care of people with Alzheimer’s disease. During years of
care-giving, families experience emotional, physical, and financial stresses.
It is impossible to quantify this suffering.
In 2000, the direct and total national cost to the USA
was nearly
US$ 536 billion and
US$ 1.75 trillion respectively.
These are minimum estimates of the long-term dollar losses
to the USA
due to Alzheimer’s disease.
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