Caffeine, a natural component of coffee and tea, is the most commonly consumed psychoactive substance in the world. It has well-documented effects on mental alertness. Caffeine, and possibly coffee, might promote long-term brain health, but the evidence is inconclusive. It is particularly unclear whether an elderly individual who increases coffee consumption later in life will benefit or be harmed.
Several meta-analyses and systematic reviews exist, though no clinical trials have studied the effects of caffeine on brain health or dementia prevention . Our search identified:
• Multiple meta-analyses and systematic reviews of observational studies
• 0 randomized controlled trials on whether caffeine or coffee can reduce risk of dementia
• Multiple observational studies
• Multiple preclinical studies 
Evidence suggests that caffeine has cognitive benefits, including alertness and attention [4-6]. Human studies on whether long-term use of coffee or caffeine can reduce risk of cognitive decline or Alzheimer's disease are inconclusive. Meta-analyses and systematic reviews of observational studies report that drinking coffee can either provide a long-term benefit to brain health or have no effect . These observational studies have a number of issues that result in inconsistencies. For instance, it is unknown whether people who drink coffee share other aspects of health and lifestyle that might be responsible for better brain health. In addition, coffee and caffeine consumption are rarely measured in the same way between studies.
Even if long-term coffee intake does promote brain health, it is unclear whether elderly people might reduce their risk of Alzheimer's if they start drinking coffee later in life. In one study, cognitively normal elderly people who increased their consumption of caffeine were at a greater risk of developing mild cognitive impairment (MCI) . The acute cognitive benefits from coffee may also decrease with age, eventually causing cognitive deficits . However, in another study, individuals with MCI were less likely to progress to dementia if they had higher caffeine levels in their blood .
The results to-date on caffeine and APOE4 status are inconsistent . For more information on what the APOE4 gene allele means for your health, read our APOE4 information page.
Few studies have examined whether coffee or caffeine is beneficial to patients with dementia. One study reported that caffeine consumption in elderly patients with dementia improved some physical symptoms and apathy, but it interrupted sleep when consumed after 6 pm . Another study reported that individuals with mild cognitive impairment (MCI) were much less likely to progress to dementia if they had higher caffeine levels in their blood . These studies, however, did not directly assess whether caffeine promotes brain health in individuals with MCI or dementia. In addition, people with dementia often suffer sleeping problems and are sometimes taken off caffeine for this reason. If caffeine impairs sleep, it could also impair cognitive function or even accelerate cognitive decline.
Moderate coffee and caffeine intake (200–300 mg/day or 1–3 cups of coffee) is generally considered safe . At high doses, however, it may cause anxiety . Caffeine may decrease performance in some elderly individuals . People with a history of cardiovascular or high blood pressure problems should consult their physician or healthcare provider about consuming caffeine. Caffeine can also interact in dangerous ways with some medications and reduce the effects of others. The U.K. Food Standards Agency recommends pregnant women not consume more than 200 mg of caffeine per day.
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Coffee is the primary source of dietary caffeine and most human observational research on caffeine's benefits are based on coffee. Generally, one cup of coffee contains 95–200 mg caffeine while one cup of tea contains about 14–70 mg . The caffeine content of sodas and energy drinks can range from 25–60 mg and higher per 12 oz. can, although the sugar content of such beverages may promote obesity and diabetes, which are risk factors for dementia. Additionally, caffeine is available as a dietary supplement in pill form, often in doses of 100–200 mg. For protection against cognitive decline and dementia, there is no evidence for or against caffeine supplements or energy drinks, though adverse health effects have been reported for some energy drinks.
Additional information on caffeine doses in common drinks can be found at the Mayo Clinic.
More information on the health effects of coffee can be found at the Institute for Scientific Information on Coffee.
The Center for Science in the Public Interest provides information on caffeine levels in different foods and drinks.
Check for drug-drug and drug-supplement interactions on Drugs.com.