Web edition: August 16, 2007
Although wine may improve with age, the human body tends to falter during the so-called golden years. Among the most exasperating declines occur in memory and critical aspects of reasoning. However, downing plenty of caffeine-rich coffeeor teamay offer one low-cost solution for keeping aging wits sharp, a French study finds. The rub: This strategy appears to benefit only women.
Karen Ritchie of the French National Institute of Health and Medical Research (abbreviated in French as INSERM) in Montpellier and her colleagues recruited more than 7,000 men and womenall 65 and olderfrom the cities of Bordeaux, Dijon, and Montpellier. All took a battery of tests to measure how nimble their minds were. Then 2 and 4 years later, each study volunteer still living took the tests again. The scientists correlated test scores with information on each participant's diet, prescribed medicines, medical historyespecially heart disease and depressionand even such details as education and income.
Mental acuity tended to diminish over the 4 years of follow-up throughout the population, Ritchie's team found. However, women who drank three or more cups of coffee per day stayed sharper, on average, than those who drank less of the brew. Ladies who downed six or more cups of regular tea per dayan amount delivering caffeine about equal to the critical coffee dosereceived comparable cognitive protection, the researchers report in the Aug. 7 Neurology.
No matter how the researchers analyzed their data, they could find no evidence that heavy caffeine intake similarly benefited any of the 2,800 participating men. Although the study's design precluded investigating the possible mechanism for a gender difference, Ritchie notes that at least one animal study published by others "suggests there's an interaction between caffeine and the [female] sex hormones estrogen and progesterone."
If caffeine's protective effect works by interacting with receptors for estrogen on a women's cells, this might explain another preliminary observation by the French team: that among heavy caffeine consumers, women over age 80 faced half the risk of significant cognitive decline during the study than ladies 65 to 80 did.
Ritchie explains that even though all the women were past menopause, the older women would tend to have less estrogen in their systems to tie up those receptors. The reason: Although all of the participants' reproductive organs had long ago shut down the hormone's production, women in the older group were less likely to be taking estrogen-replacement therapy. Moreover, a physical wasting that typically accompanies advanced age would leave less abdominal fat in the older women, and fat around the middle can produce substantial estrogen.
One disappointing observation, Ritchie notes, is that even heavy caffeine intake didn't reduce the risk of developing outright dementia, such as Alzheimer's disease. Rates of dementia diagnosis didn't vary among groups stratified by caffeine intake. However, the neuropsychologist points out, "4 years is probably too short a time period to look at this." Her group will soon have 8 years of follow-up on the study's participants and will recheck dementia rates at that time.
"I think there are so many factors that affect the development of Alzheimer's diseasein particular, genetic factorsthat something like a little coffee is not likely" to stop the mental decline associated with the disease, Ritchie says. However, she observes, there's a long time between the initial signs of cognitive impairment and the onset of debilitating symptoms that will ultimately lead to a diagnosis of Alzheimer's. "My most optimistic speculation," Ritchie says, is that caffeine might lengthen the time it takes Alzheimer's disease to fully manifest itself.
What they found
Although the caffeine content of any given cup of coffee or tea can vary, the researchers estimated a participant's daily intake on the basis of typical quantities: 100 milligrams per cup of coffee and 50 mg per cup of nonherbal tea.
Overall, two-thirds of the participants consumed more than 100 mg of caffeine per day. Among these volunteers, some 13 percent of men and 16 percent of women reported consuming more than 300 mg of caffeine daily. These figures included caffeine from prescribed medications, which were generally minor contributors.
People with high blood pressure were less likely than others to drink substantial amounts of coffee or tea. In contrast, people with atherosclerosis or other forms of heart disease were more likely to take in at least 200 mg of caffeine per day. Caffeine intake showed no link to body weight, cholesterol status, an individual's mobility, cancer, diabetes, or sleep disorders.
In men, caffeine consumption didn't correlate with scores on mental-performance tests. However, women reporting heavy caffeine consumption typically exhibited less of a decline during the 4-year-study in their scores on an Isaacs test. This exam challenges an individual to retrieve verbal material. For instance, participants might be asked to name all the animals they can think of in 90 seconds.
Women consuming the most caffeine were also less likely than those in other groups to suffer declines in their scores on a test of visual recall. Here, volunteers viewed a shape and later had to pick it out from a field of disparate shapes.
Even among women, caffeine's benefit didn't show up in all mental tests. For instance, the INSERM team found no evidence of caffeine's protective effect on women's scores on the Mini-Mental State Examination. This test, frequently used to screen for cognitive impairment in the elderly, assesses whether individuals know the date and where they are as well as their abilities to do simple arithmetic in their heads, spell a common word backwards, copy simple geometric shapes, repeat a spoken phrase, and craft a sentence.
Strength of this study
The new French study is not the first to look for a caffeine link to mental health. Indeed, Ritchie says, her research project was prompted by several promising but ultimately inconclusive studies in people. In a clearer result, high intakes of caffeine protected memory in aging rats and mice.
Researchers conducting the rodent study showed that caffeine blocked brain receptors for adenosine, a cell-signaling molecule. "By so doing," Ritchie explains, the stimulant "stopped damage" caused by amyloid-beta, the proteinlike material that accumulates in the brains of all elderly people and especially those with Alzheimer's disease.
Such data suggest "quite a good theoretical link" between caffeine and brain protection and were the underpinning her team's new study, Ritchie explains.
The earlier caffeine-cognition studies in people didn't account for many potentially confounding factors, such as whether someone with heart disease had been told to avoid caffeine, or an individual was depressed or disabled and therefore might not join in coffee klatches. These and other medical conditions might independently increase people's risk of mental decline, says Ritchie.
The new INSERM study accounted for all such potentially confounding factors. Usually, when scientists better account for such factors, associations between caffeine or other intakes and health become weaker, Ritchie notes. "In our case, however, we found that as we started to control for these other factors, our link actually became stronger."
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Institut National de la Santé et de la Recherche Médicale
E 361 Pathologies of the Nervous System
Epidemiological and Clinical Research
Hôpital La Colombière
34093 Montpellier Cedex 5
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