Study Reveals Low Doses of Caffeine Can Affect Sleep Quality

Caffeine affects adenosine signaling, which is critical in regulating the sleep-wake cycle. The study assessed how caffeine consumption impacts sleep-related electroencephalography (EEG), focusing on the low-frequency brain waves associated with deep sleep stages.

Data from 32 human studies conducted from January 1980 to January 2026 revealed that caffeine consumption can diminish the quality of deep sleep, potentially impairing the body's restorative processes. The findings showed a consistent reduction in low-frequency NREM sleep EEG activity, with one study illustrating that caffeine intake before bedtime reduced NREM sleep in late-middle-aged adults from 66 minutes to just 38 minutes in the initial three hours of sleep.

Additionally, caffeine appeared to increase faster EEG activity, which may lead to lighter, less restorative sleep. Steven Allder, MD, a consultant neurologist, noted that even small doses of caffeine, starting at 100 milligrams, can influence slow-wave brain activity early in the night. He emphasized that higher doses are likely to interfere more significantly with normal sleep patterns.

Şebnem Ünlüişler, MSc, from the London Regenerative Institute, indicated that while higher doses are generally more impactful, individual genetics, timing, and sensitivity also play crucial roles. The review underscored that caffeine consumed in the morning can still affect sleep; one study found that a dose of 200 mg shortly after waking altered brain activity during sleep, with participants reporting reduced sleep efficiency by bedtime.

Caffeine taken six hours before bed was associated with a notable drop in slow-wave sleep, showing another study reporting a reduction from 71.5 minutes to 48.9 minutes. However, consuming caffeine right at bedtime still led to a slight reduction in deep sleep, although the decrease was smaller.

The review authors pointed out limitations in the studies reviewed, particularly a lack of representation among older adults, adolescents, and individuals with existing sleep problems or psychiatric conditions. Variations in genes like ADORA2A were noted to potentially influence how caffeine impacts sleep quality.

Experts suggest that there is no universal cutoff time for caffeine consumption, with factors such as age, metabolism, and habitual caffeine intake varying by individual. Both Allder and Ünlüişler recommend focusing caffeine intake primarily in the morning or early afternoon to minimize potential sleep disturbances, advising individuals to adjust their caffeine consumption based on their personal experiences and sleep quality.