Forstmeier_Layout 1 07/10/2009 12:54 Page 20
Neurodegenerative Diseases Alzheimer’s Disease
related to risk of AD, indicating that depression seems to be a risk any-cause dementia.
Six of the 11 studies focusing on AD found an
factor for rather than a prodrome of AD.
increased risk for people with diabetes (e.g. relative risk 1.8, 95% CI
Five of the nine studies covering any-cause dementia
One possible explanation for the association between depression and reported an increased risk for people with diabetes (e.g. relative risk
risk of AD is that depression may lead to increased cortisol levels in 1.5, 95% CI 1.0–2.2).
There was no clear difference in findings for
the hippocampus, and that prolonged exposure to cortisol contributes diabetes in mid- versus late life.
to hippocampal atrophy and, in the long run, to AD. If this is the case,
people who are susceptible to psychological stress such as depression Hypertension
(i.e. people with the personality trait of neuroticism) should have a Five of 11 studies found an increased risk of AD in people with
higher risk of AD. Three longitudinal studies investigated this association hypertension (e.g. relative risk 4.5, 95% CI 1.5–13.1).
Five of six
and found that pre-morbid proneness to psychological stress slightly studies found an increased risk of any dementia (e.g. relative risk 4.0,
increases the risk of AD (relative risk 1.05, 95% CI 1.01–1.09).
95% CI 1.6–10.3).
However, some studies showed that either
elevated systolic or elevated diastolic blood pressure was associated
Physical Activity with an increased risk of AD. There was a marked difference in
Sixteen studies were identified that investigated the relationship findings for hypertension in mid- versus late life. All studies assessing
between participation in regular (daily) physical activities (e.g. walking, blood pressure at mid-life found a significant association between
dancing, swimming) in mid- to late life and risk of AD and dementia. hypertension and AD/dementia, compared with only one study
Most (12) studies found a reduced risk of AD in individuals who assessing blood pressure in late life.
frequently participated in physical activities (e.g. relative risk 0.6, 95%
The majority of these studies investigated the effect of Hypercholesterol
physical activity in old age. However, a protective effect of physical Two of four studies found an increased risk of AD in people with
activity in middle age has also been reported.
Several possible elevated total cholesterol (e.g. relative risk 2.8, 95% CI 1.2–6.7).
mechanisms may underlie this association, including reduction of of six studies found an increased risk of any dementia (e.g. relative
vascular risk factors, promotion of brain plasticity and brain reserve risk 2.6, 95% CI 1.2–6.0).
The studies reporting a significant
and general cognitive ability resulting in better health behaviour. association between high cholesterol and risk of AD/dementia
assessed cholesterol levels in mid-life; all others assessed cholesterol
Social Activity and Social Network levels in late life.
Several longitudinal studies have investigated the protective effects
of social factors such as social activity and social network on risk of Obesity
AD and dementia. Only one of five studies found an increased risk of AD in people with
obesity (relative risk 1.4, 95% CI 1.2–1.6).
Five of seven studies
Social Activity found an increased risk of any dementia (relative risk 1.1, 95% CI
Four studies were identified that investigated the relationship between 1.04–1.2).
Generally, studies that measured weight at mid-life
participation in regular social activities (e.g. going to the theatre, compared with late life showed a more consistent association and a
participating in social groups, visiting friends) in late life and risk of higher risk of dementia.
dementia. All studies found a reduced risk of dementia in individuals
who frequently participated in social activities (e.g., relative risk 0.6, In conclusion, the deleterious effects of vascular risk factors that are
95% CI 0.4–0.9).
Several possible mechanisms may underlie this already present in mid-life seem relatively clear. These factors may
association, including promotion of brain plasticity and brain reserve, play a causal role in AD by influencing neurodegenerative processes
and emotional health resulting from fulfilling relationships. in the brain. Negative effects of vascular risk factors present in late
life seem less evident. Findings also show that the risk of AD and
Social Network dementia increases with the number of vascular risk factors.
The latter hypothesis can also be tested by investigating the social
network as a risk factor (e.g. being single or divorced versus married). Nutrition
Four studies were identified that investigated the relationship Several nutritional factors have been investigated as potential risk
between social network and risk of dementia. All studies found an factors for AD and dementia in recent years. The question is which
increased risk of dementia in individuals with poorer social networks nutrients are essential for the healthy functioning of the brain.
(e.g. relative risk 2.3, 95% CI 1.3–4.7).
Rich social networks provide
emotional support and cognitive simulation. Vitamins
Three of four studies (see reference 6 for an overview) found an
Vascular Risk Factors increased risk of AD in people with a high homocysteine level (e.g.
The components of metabolic syndrome – diabetes, hypertension, relative risk 1.8, 95% CI 1.3–2.5).
, vitamin B
hypercholesterol and obesity – are well-known risk factors for have often been investigated simultaneously. Six studies were
cardiovascular disease. There is also accumulating evidence that they identified that tested the associations between these vitamins and
are risk factors for AD and dementia in general. Treatment of these risk of AD.
In five of these studies, high folate intake in late life was
conditions is thus an important target for prevention of dementia. found to reduce the risk of AD (e.g. relative risk 0.4, 95% CI 0.2–0.8).
intake was associated with risk of AD in only one of four
Diabetes studies, and B
intake in none of the studies.
It has also been
A recent systematic review identified 13 studies investigating the speculated that intake of antioxidative vitamins E, C, flovoid and beta-
relationship between diabetes in mid- to late life and risk of AD or of carotene might influence risk of AD. Ten studies on these associations
20 EUROPEAN NEUROLOGICAL REVIEW