A sleep study (polysomnography) is a non-invasive overnight test used to diagnose various sleep disorders by recording brain waves, blood oxygen levels, heart rate, breathing, and leg movements during sleep. While you can eat before the procedure, strict rules about timing and substance avoidance must be followed for accurate results. These preparatory steps ensure the monitored sleep is as close to your typical, natural sleep pattern as possible. Failing to follow the guidelines risks skewing the data, which could lead to an incorrect diagnosis or an unnecessary second study.
Establishing the Eating Cutoff Time
Plan to eat your final meal several hours before your scheduled arrival time at the sleep center. Most facilities recommend finishing dinner approximately two to three hours before the study is set to begin. This timing prevents indigestion, heartburn, or acid reflux, which can interfere with the ability to fall asleep and stay asleep. Any discomfort from a recent meal could distort the results, as the goal is to observe your natural sleep.
The type of food consumed is also important. Heavy, greasy, or spicy meals take longer to digest and are more likely to cause nocturnal gastrointestinal upset, so opting for a light, bland meal is advisable. It is recommended to avoid eating anything once you arrive at the lab, as the focus shifts to preparing the monitoring sensors and beginning the study promptly.
Mandatory Avoidance of Stimulants and Alcohol
Substances that alter the central nervous system must be strictly avoided for a considerable period before a sleep study. Alcohol, caffeine, and nicotine are the most common substances that can fundamentally affect sleep architecture and compromise the validity of the polysomnography. Many clinics advise against consuming any of these substances after noon on the day of the test, and some recommend a longer abstinence period of 24 hours or more for alcohol.
Caffeine is a stimulant that increases wakefulness and delays sleep onset; it is found in coffee, tea, soda, and chocolate. Alcohol, though initially sedating, is disruptive because it fragments sleep, suppresses Rapid Eye Movement (REM) sleep, and exacerbates the relaxation of throat muscles. For those tested for sleep apnea, this muscle relaxation can worsen breathing events, leading to an artificially severe result. The suppression of REM sleep can also mask certain conditions, such as mild sleep apnea that only occurs during the REM stage.
Guidelines for Prescription and Over-the-Counter Medications
Managing your regular medications requires a consultation with your sleep physician or the sleep clinic staff well before the study date. The general rule is that you should continue taking all your prescribed medications unless you are explicitly instructed to stop them. Stopping a medication without guidance can be dangerous and may invalidate the study by observing an altered baseline state.
Certain drugs, such as sleep aids, anti-anxiety medications, and some pain relievers, can mask or mimic symptoms of sleep disorders. Medications that induce sleep, for instance, may suppress the very symptoms the study is trying to capture. If your doctor determines a specific medication could interfere with the diagnostic goal, they may ask you to temporarily discontinue it for a set period, which could be days or weeks for tests like the Multiple Sleep Latency Test (MSLT). Always bring a complete list of all medications and supplements for review with the technician.