Re: Systematic Review Finds Long-term Coffee, Tea, and Caffeine
Consumption May Reduce the Risk of Cognitive Disorders Associated with
Aging
Panza
F, Solfrizzi V, Barulli MR, et al. Coffee,
tea, and caffeine consumption and prevention of late-life cognitive decline and
dementia: a systematic review. J
Nutr Health Aging. March 2015;19(3):313-328.
As
life expectancy has increased, the incidence of aging-related disorders has
also increased globally. These disorders include cognitive decline, such as
mild cognitive impairment (MCI), dementia, and Alzheimer's disease (AD). AD is
associated with intraneuronal and extraneuronal protein aggregates, some of
which form plaques on neurons. Treatment of AD has focused on decreasing
aggregate load, but more recently the focus has shifted to prevention of
aggregate formation in the decades before onset of the disease. Some evidence
suggests increasing intake of fruits, vegetables, fish, and monounsaturated and
n-3 polyunsaturated fatty acids can reduce the risk of AD and other types of
dementia and cognitive decline. Other evidence suggests that caffeine intake
can reduce the risks of neurologic disorders. Animal studies have found that
caffeine can reduce oxidative stress and the neuronal plaques associated with
AD. The goal of this systematic review was to investigate the relationship of
coffee (Coffea spp., Rubiaceae), tea
(Camellia sinensis, Theaceae), and
caffeine consumption with cognitive ability in older subjects.
The
databases PubMed, Ovid MEDLINE, EMBASE, Google Scholar, Web of Science, and
Scopus were searched for the terms coffee, tea, or caffeine in combination with
the terms cognitive impairment, decline or deterioration, dementia, Alzheimer's
disease, or mild cognitive impairment. The databases were searched for studies
published in any language before January 2014. Human, cross-sectional and
longitudinal, population-based studies and case-controlled studies were
included. Of the 631 studies found from the search, 28 met all of the criteria
and were included in the review.
Most
of the cross-sectional studies (n = 10) reviewed found an increase in measures
of cognitive ability with caffeine intake. In one study with subjects under the
age of 50, cognitive function increased with coffee consumption. In all but one
of the remaining cross-sectional studies, some or all of the measures of
cognitive ability were positively correlated with caffeine intake. In five of
the studies, coffee, tea, or caffeine intake resulted in increased cognitive
function. In one study conducted within a Chinese population, tea consumption
increased cognitive function in men but not women. In another study, caffeine
intake increased cognitive function in only one of 12 cognitive tests.
In
three of the longitudinal population-based studies (n = 12), caffeine intake
showed no effect on cognitive ability. In seven of the longitudinal studies,
coffee, tea, or caffeine intake was associated with a decrease in cognitive
decline. One study found that patients with MCI were less likely to progress to
dementia as plasma levels of caffeine increased. A review of longitudinal
studies cited found a consistent increase in cognitive ability with tea
consumption. While an effect on cognitive ability was also found with coffee
consumption, it was less consistent than that found with tea.
The
results of the cross-sectional studies that specifically addressed dementia,
AD, and MCI had mixed results. One showed no protective effect of caffeine on
these neurological disorders, while another found a positive effect of caffeine
on AD, and another found a positive effect in men in the highest quartile of
caffeine consumption. Of the seven longitudinal studies that measured the
effect of coffee, tea, and caffeine consumption on neurologic disorders, three
found no associations, while three found a positive effect of coffee but not
tea. One meta-analysis found that coffee consumption lowered the risk of
developing AD.
In
general, cognitive ability and a reduction in risk of cognitive disorders
associated with aging appear to be associated with long-term coffee, tea, and
caffeine intake. There appears to be a stronger correlation between cognitive
ability and tea consumption than coffee and a stronger correlation between
reduction in cognitive disorders and coffee consumption than tea. There also
appeared to be a stronger effect found in women than men. Some of the studies
cited in this review found no correlation between long-term coffee, tea, or
caffeine intake and cognitive ability or cognitive disorders. There is evidence
that both caffeine and other compounds found within tea and coffee reduce
oxidative stress. But, it is still unclear if the positive effects seen on
cognitive decline are a result of caffeine alone or in combination with these
other compounds.
There
are several limitations found in the studies cited in this review. The most
important is the lack of correlation among the studies themselves. Additionally,
factors, such as diet and lifestyle, may be correlated with coffee, tea, and
caffeine consumption and may influence cognitive function and decline. Other
compounds found in coffee and tea may also affect cognitive function and slow
cognitive decline. Lastly, total amounts of caffeine can vary greatly with the serving
size, source, and processing of coffee or tea so that caffeine intake can be
vastly different from one cup of coffee or tea to the next. Further studies
should control for factors including actual caffeine intake, gender, lifestyle,
diet, alcohol consumption, and smoking. Additionally, the authors state that future
studies would benefit from the inclusion of neuroimaging to measure plaque
formation associated with neurodegenerative diseases.
–Cheryl
McCutchan, PhD
