More than 75 percent of the U.S. population drinks coffee and about 50 percent report drinking it daily (J Nutr, 2016 Sep; 146(9): 1762–1768). If you ask people why they drink coffee, you will most often be told that it makes them more alert so that they can do their work more efficiently. A recent study of MRIs of the brains of habitual coffee drinkers found that coffee, but not caffeine alone, increased activity of the parts of the brain regulating vision and executive function (Front Behav Neurosci, June 28, 2023;17).

To find out why coffee drinkers appear to be more alert after drinking coffee, the researchers tested 83 people who drank at least one cup of coffee every day.
• 47 of the people were scanned before drinking their morning cup of coffee, then again 30 minutes after they drank a cup.
• 36 people were scanned in the same way after they drank the same amount of caffeine in plain hot water.
The MRI scans found that both groups had decreased activity in a part of the brain that is activated when they go to sleep, so both groups were more alert. However, only the coffee drinkers had increased activity in parts of the hippocampus in the brain involved in short-term memory, attention and focus, while ingesting caffeine in water did not. The researchers did not test people who never drink coffee.

We do not know whether coffee contains something other than caffeine that makes people more alert and helps them function better, or whether regular coffee drinkers only think that they can function better because they remember the previous sight, smell and taste of coffee. Coffee contains epicatechins that have been shown in other studies to help improve memory, and chlorogenic acid, a powerful anti-inflammatory and antioxidant that helps control blood sugar and memory (Med J Malaysia, July, 2023;78(4):476-483).

Coffee May Have Other Benefits
Other studies have associated drinking coffee with reduced risk for heart attacks, some types of cancers, strokes, diabetes, dementia, Parkinson’s disease and more (Int J Mol Sci, 2023;24(3):2706; Am J Clin Nutr, 2022;116:730–740; NEJM, 2020;383:369–378; J Acad Nutr Diet, 2021;121:2221–2232.e4; Adv Nutr, 2021;12:1160–1176).

Recommended Limits
Coffee is a potent stimulant. Three cups of coffee per day is probably a safe limit for most people. The FDA recommends 400 milligrams as the upper daily limit for caffeine. An 8-ounce cup of brewed coffee contains 100mg of caffeine, while an 8-ounce cup of brewed tea contains 50mg.

However, some people should take less, such as those who suffer symptoms such as sweating, shaking, anxiety or heart palpitations after drinking coffee; or a significant increase in heart rate or blood pressure. It can take up to 10 hours to clear caffeine from your bloodstream. Certain medications can slow down caffeine metabolism, such as oral contraceptives, certain antidepressants, heart drugs or antibiotics.

My Recommendations
Coffee can make you feel more alert and help you to concentrate. Taking in fewer than four cups of coffee per day appears to offer certain health benefits; however, coffee contains potent stimulants that can cause irregular heartbeats and raise blood pressure in susceptible people. If you have high blood pressure or heart problems, you may want to get your doctor’s opinion on your coffee habits.