Guidelines generally advise not drinking more than four cups of coffee a day. The timing of consumption matters as well: consuming coffee too early can raise stress and may disturb sleep later in the day. This conclusion has been reflected in reports from health outlets such as Daily Mail.
Most medical professionals suggest keeping caffeine intake to about 400 milligrams per day, roughly equivalent to four cups of coffee. People often notice a boost in alertness within about five minutes of sipping coffee. The peak effects usually occur between 15 minutes and two hours after ingestion, influenced by factors like recent meals and the rate at which caffeine is metabolized. Individual responses vary due to genetics, with some people clearing caffeine from their system for up to ten hours.
The speed of caffeine metabolism plays a direct role in how it affects sleep. Research indicates that excessive caffeine consumption or intake late in the day can shorten sleep by about 30 minutes in people who metabolize caffeine normally, and by as much as an hour in slow metabolizers. A 2017 meta-analysis also found that drinking coffee in the evening can disrupt slow-wave sleep, a vital stage of rest, and insufficient sleep is linked to several health concerns, including heart disease, kidney disease, high blood pressure, and diabetes. For this reason, many doctors recommend stopping caffeine six to eight hours before bedtime or earlier (citation: health studies).
To maximize energy while minimizing tension, avoid drinking coffee too early in the day, ideally after 9:30 to 11:00 a.m. Morning cortisol levels—often described as a stress hormone—tend to be highest upon waking, with a noticeable decline around 9:30 in the morning and another drop around 1:00 p.m. in the afternoon (citation: endocrinology research). This pattern helps explain why caffeine timing can influence perceived energy and stress levels throughout the day.
Historical notes suggest that hydration and diet play roles in kidney stone prevention, with some early studies exploring whether caffeine intake impacts stone risk. While the topic has evolved, current guidance emphasizes balanced caffeine use as part of a broader approach to kidney and urinary health (citation: nutrition history review).