Both
long term abstinence and heavy drinking may increase dementia risk
But the underlying
mechanisms are likely to be different in the two groups
BMJ
People who abstain
from alcohol or consume more than 14 units a week during middle age (midlife)
are at increased risk of developing dementia, finds a study in The
BMJ .
However, the
underlying mechanisms are likely to be different in the two groups.
As people live longer,
the number living with dementia is expected to triple by 2050. So understanding
the impact of alcohol consumption on ageing outcomes is important.
Previous studies
indicate that moderate drinking is associated with a reduced risk of dementia,
whereas both abstinence and heavy drinking are associated with a risk of
dementia. But the evidence is far from conclusive, and the reasons underlying
these associations remain unclear.
So a team of researchers from Inserm (French National Institute of Health and Medical Research) based in France and from UCL in the UK set out to investigate the association between midlife alcohol consumption and risk of dementia into early old age.
They also examined whether cardiometabolic disease (a group of conditions including stroke, coronary heart disease, and diabetes) has any effect on this association.
Their findings are
based on 9,087 British civil servants aged between 35 and 55 in 1985 who were
taking part in the Whitehall II Study, which is looking at the impact of
social, behavioural, and biological factors on long term health.
Participants were
assessed at regular intervals between 1985 and 1993 (average age 50 years) on
their alcohol consumption and alcohol dependence.
Alcohol consumption
trajectories between 1985 and 2004 were also used to examine the association of
long term alcohol consumption and risk of dementia from midlife to early old
age.
Admissions for alcohol
related chronic diseases and cases of dementia from 1991, and the role of
cardiometabolic disease were then identified from hospital records.
Of the 9,087
participants, 397 cases of dementia were recorded over an average follow-up
period of 23 years. Average age at dementia diagnosis was 76 years.
After taking account
of sociodemographic, lifestyle, and health related factors that could have affected
the results, the researchers found that abstinence in midlife or drinking more
than 14 units a week was associated with a higher risk of dementia compared
with drinking 1-14 units of alcohol a week.
Among those drinking above 14 units a week of alcohol, every 7 unit a week increase in consumption was associated with 17% increase in dementia risk.
Among those drinking above 14 units a week of alcohol, every 7 unit a week increase in consumption was associated with 17% increase in dementia risk.
In the UK, 14 units of
alcohol a week is now the recommended maximum limit for both men and women, but
many countries still use a much higher threshold to define harmful drinking.
History of hospital
admission for alcohol related chronic diseases was associated with a four times
higher risk of dementia.
In abstainers, the
researchers show that some of the excess dementia risk was due to a greater
risk of cardiometabolic disease.
Alcohol consumption
trajectories showed similar results, with long term abstainers, those reporting
decreased consumption, and long term consumption of more than 14 units a week,
all at a higher risk of dementia compared with long term consumption of 1-14
units a week.
Further analyses to
test the strength of the associations were also broadly consistent, suggesting
that the results are robust.
Taken together, these
results suggest that abstention and excessive alcohol consumption are
associated with an increased risk of dementia, say the researchers, although
the underlying mechanisms are likely to be different in the two groups.
This is an
observational study, so no firm conclusions can be drawn about cause and
effect, and the researchers cannot rule out the possibility that some of the
risk may be due to unmeasured (confounding) factors.
The authors say their
findings "strengthen the evidence that excessive alcohol consumption is a
risk factor for dementia" and "encourage use of lower thresholds of
alcohol consumption in guidelines to promote cognitive health at older
ages."
They also say these findings "should not motivate people who do not drink to start drinking given the known detrimental effects of alcohol consumption for mortality, neuropsychiatric disorders, cirrhosis of the liver, and cancer"
They also say these findings "should not motivate people who do not drink to start drinking given the known detrimental effects of alcohol consumption for mortality, neuropsychiatric disorders, cirrhosis of the liver, and cancer"
This study is
important since it fills gaps in knowledge, "but we should remain cautious
and not change current recommendations on alcohol use based solely on
epidemiological studies," says Sevil Yasar at Johns Hopkins School of
Medicine, in a linked editorial.
She calls for further
studies and ideally a government funded randomized clinical trial to answer
pressing questions about the possible protective effects of light to moderate
alcohol use on risk of dementia and the mediating role of cardiovascular
disease with close monitoring of adverse outcomes.
In summary, she says,
"alcohol consumption of 1-14 units/week may benefit brain health; however,
alcohol choices must take into account all associated risks, including liver
disease and cancer."