Coffee and tea have long been applauded for their strong antioxidant properties and ability to combat inflammation. During the past few years, several experiments using animals have suggested that the benefits of these beverages may come primarily from their caffeine content. For example, a 2012 study reported the results of administering caffeine to mice that had a genetic predisposition for Alzheimer’s. As a result, these mice experienced reduce cognitive decline, amyloid-beta plaque levels, and rates of neuronal death. However, studies on humans have been less consistent, with some reporting reduced rates of dementia among high consumers of caffeine, and others finding no relationship at all.
A study published last week in the Journals of Gerontology: Medical Sciences attempted to end the caffeine debate once and for all. The study involved a cohort 6,467 women between the ages of 65 and 80 who were part of the Women’s Health Initiative Memory Study. At the beginning of the study, the women were asked to report their normal daily consumption of caffeine. Based on this information, the researchers categorized them as low (<50th percentile) or high (>50th percentile) caffeine consumers. The low-caffeine group consumed an average of 64 mg per day, which is the equivalent of 5 oz of coffee (half of a large mug). The high caffeine consumers consumed an average of 261 mg per day, the equivalent of 22 oz of coffee (2-3 large mugs). The women’s caffeine consumption appeared to stay fairly constant during the course of the study.
After an average of seven years, each woman underwent a cognitive assessment to determine the presence of dementia. Women who consumed high amounts of caffeine were 26% less likely to be diagnosed with probable dementia or cognitive impairment in the follow-up assessment. They also had a reduced risk of Parkinson’s disease and scored better on a test of global cognitive function called the Modified Mini Mental State Exam (MMMSE).
Notably, the researchers pointed out that the association between cognitive impairment and caffeine intake was dampened when baseline MMMSE scores were taken into account. In other words, the high consumers of caffeine may have had higher cognitive function than the low caffeine consumers to begin with. Thus, it makes sense that they’d have reduced cognitive impairment at the follow-up, since they initially had a “head start,” regardless of their actual caffeine consumption. Future studies will need to investigate this possible confounding variable.
This study was fairly homogenous, with all of the subjects being postmenopausal women who were generally healthy and well-educated. Accordingly, the results can’t be generalize to other populations. There is also the possibility that the women’s self-reported caffeine intake may have differed from their true intake, especially since caffeine intake was only monitored based on coffee and tea, thus excluding soda and other caffeinated foods/beverages.
Overall, this study is not sufficient to conclusively say whether caffeine is protective against dementia, despite the recent popular science headlines claiming otherwise. Since in general the health benefits of coffee and tea seems to outweigh any negatives, it’s probably fine to continue consuming them if you do so normally (within the advice of your doctor, of course). However, there’s not enough evidence yet to recommend increasing caffeine intake for neuroprotective purposes.