Alzheimer’s disease (AD) is the most common cause of dementia for which there are currently limited treatment options, some of them with potential adverse effects. In this context, modifiable risk factors, which include lifestyle habits (e.g. diet), have gained attention. Coffee may offer benefits for brain health by reducing the inflammation of the nervous tissue. In fact, several studies suggest that caffeine exposure may influence the pathogenic process of AD. Moreover, caffeine has also been reported to improve the sensitivity to insulin and vascular function, both of which may help protect the brain against cognitive decline. Several studies have examined the relationship between the intake of coffee and caffeine and brain health and the dose-response relationship between dementia risk and caffeine intake. However, the findings remain inconsistent.
In a recent study published in The Journal of the American Medical Association (JAMA), a team of researchers led by Mr. Zhang and Dr Liu (T.H. Chan School of Public Health, Harvard University, and Brigham and Women’s Hospital and Harvard Medical School, Harvard University, Boston, US), examined the association between the consumption of caffeinated coffee and tea with the risk of dementia and cognitive performance.
The authors used data from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The NHS enrolled 121,700 women aged 30 to 55 years and started in 1976. The HPFS began in 1986 and enrolled 51,529 male health professionals aged 40 to 75 years at baseline. The study began at the moment when diet was first assessed in both cohorts (1980 for the NHS cohort and 1986 for the HPFS cohort) and the duration of the follow-up was 43 years. In both cohorts, participants were excluded if they had history of cancer, Parkinson’s disease or dementia or did not consume caffeinated beverages. After exclusions, 86,606 women in the NHS cohort and 45,215 men in the HPFS cohort were included in the analysis (mean age 46.2 in the NHS cohort and 53.8 years in the HPFS cohort at baseline; 65.7% were female).
At baseline, and every two to four years thereafter, questionnaires were sent to the participants to help researchers collect information on lifestyle factors and health conditions. In the questionnaires, participants reported how often they consumed each food and beverage. Caffeine intake was derived from intake levels of coffee, tea, soda, and chocolate. Dementia cases were identified through death records or biennial self-reported diagnosis of AD or other types of dementia. Subjective cognitive decline was assessed using questionnaires covering general memory, executive function, attention, and visuospatial skills. Objective cognitive function was also evaluated using telephone-based cognitive tests from 1995 to 2008.
Researchers observed that women consumed a median of 4.5 cups of coffee or tea per day, whereas men consumed 2.5 cups per day. During the follow-up, 11,033 cases of dementia were identified, and a higher level of caffeinated coffee intake was associated with a lower risk of dementia. In a similar way, higher tea intake was associated with lower dementia risk. Decaffeinated coffee intake was, in contrast, not associated with dementia risk. Regarding the associations of caffeinated coffee and tea intake with subjective cognitive decline, the findings were similar. In the NHS cohort, higher intake of caffeinated coffee was also associated with slightly better cognitive performance.
The authors found that consumption of approximately two to three cups per day of caffeinated coffee, one to two cups of tea per day, or 300 mg/d of caffeine was associated with the lowest risk of dementia compared with no consumption. Similar patterns were also observed for subjective and objective cognitive decline.
The results highlight that in these two cohorts with participants assessed for their diet repeatedly and during a long period of time, higher intake levels of caffeinated coffee, tea and caffeine were associated with a reduced risk of dementia. These findings were also corroborated by the lower prevalence of subjective cognitive decline and modestly better cognitive function in participants consumed caffeinated beverages. Important to note is that the strongest protective associations between dementia risk, cognitive performance and caffeinated beverages was observed when the consumption level was moderate. In addition, this link was independent of genetic predisposition and other risk factors for dementia.
Although higher moderate consumption of caffeinated coffee and tea was associated with reduced risk of dementia and better cognitive performance, further research is needed to understand the pathways by which caffeinated and decaffeinated beverages influence brain health.
https://jamanetwork.com/journals/jama/article-abstract/2844764
