Tea Drinking May Help Protect Against Cognitive Impairment and Decline

July 14, 2008 — Regular tea consumption was associated with lower risks for cognitive impairment and cognitive decline, according to the results of a study reported in the July issue of the American Journal of Clinical Nutrition.

“Laboratory research suggests that tea has potential neurocognitive protective effects, but this is not established in humans,” writes Tze-Pin Ng, from the University of Singapore, and colleagues. “In recent decades, experimental and epidemiologic studies have associated tea with a wide variety of health benefits, such as the prevention of cardiovascular diseases, cancer, and mortality. Although the findings are somewhat inconsistent, most appear to support tea’s favorable effects.”

The goal of this study was to determine the relationship between tea intake and cognitive impairment and cognitive decline among community-living Chinese adults 55 years or older in the Singapore Longitudinal Ageing Studies cohort. Tea consumption was evaluated at baseline, and participants completed the Mini-Mental State Examination (MMSE) at baseline and 1 to 2 years later.

The investigators performed a cross-sectional analysis of baseline data from 2501 participants and longitudinal analysis of data from 1438 cognitively intact participants, and they calculated odds ratios (ORs) of association in logistic regression models that adjusted for potential confounders.

Independent of other risk factors, total tea intake was significantly associated with a lower prevalence of cognitive impairment, defined as an MMSE score of 23 or less. Compared with ORs for rare or no tea intake, ORs for low, medium, and high levels of tea intake were 0.56 (95% confidence interval [CI], 0.40 – 0.78), 0.45 (95% CI, 0.27 – 0.72), and 0.37 (95% CI, 0.14 – 0.98), respectively (P for trend < .001).

For cognitive decline, defined as a decrease in MMSE score of 1 or more points, the corresponding ORs were 0.74 (95% CI, 0.54 – 1.00), 0.78 (95% CI, 0.55 – 1.11), and 0.57 (95% CI, 0.32 – 1.03), respectively (P for trend = .042). Black (fermented) and oolong (semi-fermented) teas, the predominant types consumed by this population, were associated with the most prominent effects. There was no apparent association between coffee intake and cognitive status.

“Regular tea consumption was associated with lower risks of cognitive impairment and decline,” the study authors write.

Limitations of this study include possible residual and unmeasured confounding and difficulty detecting small effects on cognitive decline with the MMSE.

“The potential effect of tea drinking in protecting against the cognitive decline of advanced age thus has great significance, given the rapid aging of the population and the rising prevalence of vascular and Alzheimer-type dementia,” the study authors conclude. “Because tea is cheap, nontoxic, and widely consumed, it has a huge potential effect in promoting cognitive health and perhaps delaying the onset of dementia. Further studies should investigate whether tea consumption lessens the risk of vascular and Alzheimer-type dementia.”

The Biomedical Research Council, Agency for Science, Technology and Research supported this study. The study authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2008;88:224-231.

Clinical Context

Black tea accounts for approximately 72% of the world’s total tea production. A variety of health benefits have been attributed to consumption of black and green tea, including cardiovascular health, cancer prevention, and cognitive benefits, but studies have not focused on the beneficial effects of black vs green tea.

This is an observational study of community-dwelling Chinese elderly patients from Singapore, 55 years and older, to examine the association between black tea consumption and cognitive impairment and cognitive decline with time.

Study Highlights

• Subjects were from the Singapore Longitudinal Ageing Studies cohort of community-dwelling adults 55 years and older who were recruited by door-to-door census.
• 2501 participants were included after those with incomplete data were excluded.
• The association between black tea consumption and baseline cognitive function was ascertained with this cohort.
• MMSE was assessed at baseline and 1 to 2 years later (median, 16 months) in 1438 (65.5%) participants, and decline in cognitive function was assessed in this cohort.
• For the longitudinal analysis, those with baseline MMSE score of less than 23 were excluded.
• Tea consumption was assessed by habitual intake with use of indigenous terms such as Ceylon or English tea, Chinese tea, and green tea.
• Chinese tea included both Chinese black and oolong (semi-fermented) tea.
• The frequency of consumption was coded from 0 to 6 from “never” or “rarely” to “10 or more cups daily.”
• 1 cup was defined as 215 mL, the standard serving size in local cafés.
• Participants were described as non–tea-drinkers if the sum of 3 scores was 0.
• Low, medium, and high intakes were defined by scores of 1 to 3, 4 to 6, and 7 or more, respectively.
• Tea consumption was defined as “never or rarely,” “occasionally,” and “daily.”
• Other lifestyle and demographic data were collected including physical activity measured by frequency (from “never” to “often”).
• Nearly one half of 2501 participants consumed Chinese black or oolong tea, and 40% drank English tea.
• Less than 24% habitually consumed green tea, and the proportion of daily consumers was less than 7%.
• Most had mixed tea consumption.
• Higher tea consumption was associated with younger age, lower proportions of women, higher education, higher alcohol consumption, and lower prevalence of depression.
• Those who consumed more tea had higher physical and social activity and consumed more fruits and vegetables.
• Cognitive impairment was present in 12.3% at baseline.
• Higher levels of tea consumption were associated with higher MMSE scores and lower prevalence of cognitive impairment at baseline.
• In longitudinal follow-up, higher tea consumption was associated with lower risk for cognitive decline.
• Compared with having no tea intake, those with low, medium, and high tea intake had ORs for cognitive impairment of 0.56, 0.45, and 0.37, respectively (P for trend < .001).
• For cognitive decline, the respective ORs were 0.74, 0.78, and 0.57 (P for trend = .042) for low, medium, and high tea consumption.
• Compared with no tea consumption, those with black and oolong tea consumption had significantly lower OR for cognitive impairment (OR, 0.55) and for cognitive decline (OR, 0.69).
• Increasing frequency of black or oolong tea consumption was associated with a lower risk for both cognitive impairment and decline.
• Consumption of green tea was associated with a lower prevalence of cognitive impairment but not cognitive decline, but the numbers were very small.
• The association between black tea consumption and cognitive impairment and decline was homogeneous for men and women and for older and younger seniors.
• Coffee intake was not associated with either cognitive impairment or decline.

Pearls for Practice

• Higher tea consumption in older Chinese adults is associated with younger age, male sex, higher education, higher alcohol, fruit and vegetable consumption, lower prevalence of depression, and higher physical and social activity.
• Higher tea consumption, in particular black tea consumption among older Chinese adults, is associated with a lower risk for cognitive impairment and decline.

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