July 12, 2010 (Honolulu, Hawaii) — Regular tea consumption may slow the rate of cognitive decline in cognitively normal older adults, but this protective effect does not appear to be related to caffeine, a large longitudinal study suggests.
Presented here at the Alzheimer's Association International Conference on Alzheimer's Disease 2010, results from the Cardiovascular Health Study, which examined the relationship between consumption of tea and coffee and change in cognitive function over time, showed tea drinkers had lower average annual rates of cognitive decline compared with non-tea-drinkers, ranging from 17% to 37%.
"Regular tea drinkers are essentially experiencing a different rate of cognitive decline than non-tea-drinkers," principal investigator Lenore Arab, PhD, a nutritional epidemiologist at the University of California–Los Angeles, told reporters attending a press briefing here.
|Dr. Lenore Arab|
To date, there have been 5 previous observational and cross-sectional studies looking at the potential link between coffee and cognitive function in older individuals. However, said Dr. Arab, the results have been ambiguous.
First Direct Comparison
There have only been 2 previous studies of tea and cognition, and both have suggested a protective effect, but Dr. Arab noted there has been no direct comparison of the effect of coffee and tea on cognition.
Using data on 4809 men and women aged 65 years and older from the Cardiovascular Health Study, the investigators examined the relationship between tea and coffee consumption and change in cognitive function over time.
Usual consumption was assessed at baseline using a food frequency questionnaire. Cognitive performance was assessed using the 100-point Mini-Mental State Examination (3MSE), administered at baseline and annually up to 8 times.
At baseline, 43% of participants reported drinking coffee daily, and 25% drank tea daily. The average annual rate in cognitive test scores was −1.17 for the 3MSE during a mean of 7 examinations.
The study included 5 categories of tea and coffee consumption, which included:
5 to 10 times per year
1 to 3 times per month
1 to 4 times per week
5 or more times per week
No Dose Response
Participants who drank tea 5 to 10 times per year, 1 to 3 times per month, 1 to 4 times per week, or 5 or more times per week had average annual rates of cognitive decline that were 17%, 32%, 37%, and 26% lower, respectively, than those of non-tea-drinkers.
"What is interesting here is that there does not seem to be a dose response but, rather, there seems to be a threshold effect," said Dr. Arab.
In contrast, only the highest level of coffee consumption was associated with a significantly reduced cognitive decline (20%) in 3MSE and was present for caffeinated as well as decaffeinated coffee consumption.
"In a coffee-drinking population, we do not see the same type of effect, but we do see that those who are drinking coffee regularly 5 times a week have a significantly lower, slower rate of cognitive decline, the magnitude of which is a little bit less than tea," Dr. Arab said.
Because coffee contains 2 to 3 times more caffeine than tea, the study findings suggest the protective effect is unlikely to be related to caffeine, said Dr. Arab. However, she added, the exact mechanism remains unclear.
Early in the Game
Further research is needed before any concrete recommendations can be made about tea consumption to slow cognitive decline, said Dr. Arab.
"In terms of cognition and tea we are still very early in the game. This is only the third study that suggests there may be a positive effect, but it hasn't been teased out enough to say that we know there's a clear benefit. That said, we know it's not harmful and that there may be some benefit, but we're not there yet in terms of saying anything that's definitive," Dr. Arab told Medscape Medical News.
Commenting on the study, William Thies, PhD, chief medical and scientific officer of the Alzheimer's Association, said the fact that the study did not show a clear dose response makes it difficult to interpret.
|Dr. William Thies|
"So you don't know if it is the tea that is having a direct effect or if tea is just a marker for something else, and so I'm not clear on what the findings really mean. I think we need more observational studies to tease this out," Dr. Thies told Medscape Medical News.
"I think ultimately the advice to the public is that if you like tea and you're drinking a lot of it, that's probably okay, but I'm not sure this is a clear call to recommend that everybody should drink tea," he added.
Walnuts Improve AD Symptoms in Mice
In a second diet-related study, investigators found that transgenic mice with the amyloid precursor protein gene mutation that were fed either a diet containing 6% or 9% walnuts (equivalent to 1 oz and 1.5 oz daily intake of walnuts in humans) showed significant improvement in learning, memory, emotional regulation, and motor coordination compared with transgenic mice that did not have walnuts included in their diet.
It is well-established, said principal investigator Abha Chauhan, PhD, from the New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York, that oxidative stress plays a key role in Alzheimer's disease. Furthermore, she said, it is thought that beta amyloid, a hallmark of Alzheimer's disease, can increase oxidative stress.
Walnuts are rich in substances including melatonin, vitamin E, ellagic acid, and flavonoids that have antioxidant properties.
The researchers found that dietary supplementation with walnuts in an Alzheimer's disease mouse model showed a significant improvement in memory, learning ability, anxiety, and motor development compared with their counterparts who did not receive dietary supplementation with walnuts.
"Our results suggest protective effects of walnuts in the Alzheimer's mice," said Dr. Chauhan. "Dietary supplementation of walnuts may have a beneficial effect on brain function and deserves further study."
The authors have disclosed no relevant financial relationships.
Alzheimer's Association International Conference on Alzheimer's Disease 2010: Abstract O1-06-05, Abstract O1-01-06. Presented July 11, 2010.
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