Morning Coffee May Still Disrupt Sleep Quality

Stopping coffee in the early afternoon may not fully protect your sleep. Researchers reviewed 32 earlier studies that used brain-wave monitoring and found caffeine users had lighter, more wakeful sleep than people who avoided caffeine. The difference appeared even when participants spent eight hours or more asleep, with the strongest effect during NREM sleep, the quieter phase that fills much of the night.

Caffeine blocks signals linked to the buildup of sleep pressure, which can make the brain stay more alert. It may also reduce deep N3 sleep, a stage tied to waking refreshed and supporting physical and immune recovery. One cited study found changes in brain activity at bedtime after participants took 200 mg just 10 minutes after waking.

People process caffeine at different speeds because of factors including genes, medicines, food, and metabolism. Doctors still commonly suggest ending caffeine use by 2 p.m., but another recommendation is to count backward at least eight to 10 hours from bedtime. Keeping total intake at no more than 400 mg daily may also help. Sleep-tracker information such as nighttime awakenings and resting heart rate can offer clues about whether caffeine is affecting rest.