Many of us need caffeine to stay energized throughout the day, but excessive consumption can lead to restlessness at night and anxiety during waking hours. The U.S. Food and Drug Administration recommends that adults consume no more than 400 milligrams of caffeine per day, which is roughly equivalent to about four cups of coffee. However, a more pressing question is how to optimize the amount of caffeine consumed for maximum benefit.
Astrid Nehlig, an emeritus research director at the French National Institute for Health and Medical Research, explained that about 100 to 150 milligrams—equivalent to one to one and a half cups of coffee—offers a healthful boost. She added that individuals will start to feel more alert approximately five minutes after drinking coffee, with effects peaking between 15 minutes to two hours later, depending on whether food has been consumed and an individual's metabolic rate.
However, too much caffeine can lead to negative effects, according to a report by the British "Daily Mail." A study published in the New England Journal of Medicine last year found that participants who consumed their desired amount of coffee slept on average 30 minutes less than on days when they did not consume any caffeine. Gregory Marcus, a cardiologist and professor of medicine at the University of California, San Francisco, and the lead author of the NEJM study, told The Wall Street Journal that caffeine's effect on sleep depends on how quickly it is metabolized. It can take up to ten hours for the body to fully eliminate caffeine. Genetic differences mean some individuals metabolize it slowly or quickly, experts say.
Meanwhile, the study found that people with slow metabolism slept nearly an hour less when consuming coffee, while those with fast metabolism reported no changes in their sleep patterns. Experts recommend delaying the first cup of coffee from 9:30 AM to 11 AM to gain the best energizing benefits while avoiding anxiety. If a break is taken in the afternoon, it may be preferable to choose tea, which contains about a quarter of the caffeine found in coffee. While this can help maintain energy until the end of a work shift, it may also make sleeping that night more difficult. This is because excessive caffeine disrupts sleep by blocking receptors for adenosine and melatonin hormones.
The optimal time to eliminate caffeine is six hours before sleep, or by 4 PM for those attempting to sleep by 10 PM. An analysis conducted in 2017 discovered that drinking coffee too late in the evening disrupts slow-wave sleep, the most restorative sleep period, and reduces total sleep time. Lack of sufficient sleep has been linked to a wide range of health issues, including heart disease, kidney disease, high blood pressure, diabetes, and obesity. The Centers for Disease Control and Prevention recommend that everyone get eight hours of sleep every night, but surveys indicate that one in three adults falls short of this target.
