Jury Still Out on Protective Effect of Caffeine on Cognition

Current Evidence Suggests a Stronger Effect in Women

Caroline Cassels

February 04, 2013

Evidence from existing studies in humans suggests that caffeine may help ward off cognitive decline, particularly among women. However, the number of studies is so scant that more research is needed before any definitive conclusions can be drawn.

A systematic literature review of human studies examining the effect of caffeine or caffeine-rich beverages on cognitive decline revealed that there are only 6 prospective studies that have looked at the impact of caffeine across the spectrum of cognition.

"Across the 6 studies, we found modestly reduced rates of cognitive decline over median follow-up times ranging from 1.3 years to 10 years," the authors, led by Lenore Arab, PhD, from the David Geffen School of Medicine, University of California, Los Angeles, write.

The findings are published in the January issue of Advances in Nutrition.

According to the investigators, there have been a number of animal studies indicating that caffeine may boost cognitive function. In addition, research in human populations has also suggested that coffee and tea drinkers may experience less cognitive decline as they age.

For instance, they note studies that show that global cognition scores in nondemented populations in northern Europe were positively correlated with tea intake. In addition, Asian studies of tea and cognition also suggest less cognitive impairment among tea drinkers.

However, the researchers note that such cross-sectional studies "are vulnerable to multiple biases, including the possibility that the drinking behavior may be a result of cognitive status instead of causally related."

To examine the strength of the association between tea, coffee, or caffeine consumption and the prevention of age-related cognitive decline, the investigators conducted a literature review.

The final analysis included 6 prospective, longitudinal studies published between 2003 and 2011 in which the Mini–Mental State Examination was used to establish baseline data of cognitive function and to measure cognitive function over time.

Follow-up in the studies ranged from 1.3 years to 10 years. Caffeine consumption ranged from 30 mg/week to 550 mg/week. Two studies analyzed coffee and tea consumption separately, and 1 study investigated only coffee.

All studies included in the analysis controlled for age and education. In addition, 5 studies controlled for smoking, sex, and a number of health variables.

Different outcome measures and exposure heterogeneity as well as the fact that there were not enough studies on a single exposure made it impossible to conduct a meta-analysis, the researchers report.

Despite these limitations, the investigators note that in general, "for all studies of tea and most studies of coffee and caffeine, the estimates of cognitive decline were lower among consumers, although there is a lack of a distinct dose response. Only a few measures showed a quantitative significance and, interestingly, studies indicate a stronger effect among women than men."

Dr. Arab reports that she has served as a scientific advisor to Unilever, a food company that has an interest in tea sales. The remaining authors have disclosed no relevant financial relationships.

Adv Nutr. 2013;4:115-122. Abstract