Alcohol produces both stimulating and sedating effects across the brain and body.karandaev/Getty Images
The Sleep Whisperer is a series of columns offering insights and advice about sleep health. It is not a substitute for seeking professional medical care.
Ever wondered what alcohol does to your sleep? You may feel it knocks you out to sleep like a log, and you would not be entirely wrong. But you may also notice that you don’t feel well-rested the next day. That’s because the full story of what alcohol does to our sleep is much more complex than many people realize.
Alcohol produces both stimulating and sedating effects across the brain and body. These opposing forces are part of why many people drink to facilitate sleep, only to find they feel tired in the morning. Let’s break this down.
On the one hand, alcohol initially boosts dopamine (one of the “feel good” hormones) and glucose metabolism as it ramps up in the bloodstream, with increased heart rate, energy levels and motor activation. Some of these stimulating effects are temporary, some extend into the night.
On the other hand, alcohol also enhances neurotransmitters that slow down brain activity, which eventually makes us feel sleepy. At the same time, drinking deregulates our body temperature, often resulting in night sweats. It can also cause stomach discomfort, heartburn and dehydration, which can interfere with sleep. And let’s not forget alcohol acts as a diuretic – meaning multiple awakenings for bathroom visits.
Not surprisingly, the effects on sleep are… complicated. Controlled laboratory studies show that evening drinks make us drift off quicker and, in the first part of the night, reduce awakenings and deepen sleep –so far so good.
However, as the night progresses, our body metabolizes alcohol and this gradually raises blood sugars, a phenomenon that promotes wakefulness. Our heart rate also remains elevated, which is even worse for women. Furthermore, the bulk of REM sleep is pushed later and this can trigger intense dreams and nightmares. In the second portion of the night, we start loosing deep sleep and waking up more frequently.
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Because of these delayed metabolic effects, the amount of time between drinking and going to sleep makes a difference. For instance, going for “happy hour” drinks in the late afternoon is unlikely to help you fall asleep at bedtime or have that initial transient boost in deep sleep since alcohol metabolism is too advanced by then– but it will likely lead to broken and lighter sleep.
Late night drinking is no better. Usually, our brain naturally adjusts to sleep loss by creating deeper sleep, but alcohol unfortunately blocks this compensatory mechanism. This makes it harder to recover from your sleep debt after a late night.
Another thing to keep in mind is that alcohol interacts with several sleep disorders. For instance, having more than two drinks per day is linked to higher odds of restless legs syndrome and periodic limb movement disorder. Also, the risk of sleep apnea rises progressively with the amount and frequency of drinking, and if you already have sleep apnea, alcohol makes it worse. Furthermore, a study of more than 30,000 Canadians showed that heavier drinking is associated with insomnia symptoms.
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Despite the evidence of alcohol’s negative impacts on sleep, many people continue to use it as a sleep aid – probably because it’s easier to remember how it helps us crash than what it does to us during the night. Currently, one in ten Canadians are misleadingly using alcohol in an attempt to improve their sleep. What‘s more, there is a vicious cycle where poorer sleep can lead to higher alcohol intake the next day, and heavier drinking in turn worsens the next sleep episode. Over time, drinking also changes how our body processes alcohol, so the partial soporific effects end up vanishing unless we escalate the dose.
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What if we don’t drink enormous amounts of alcohol, or just indulge every now and then? A large study from Finland suggests that even moderate drinking predicts poorer sleep quality over the next 36 years. Yet, this was worse in heavier drinkers and those who had intermittent bouts of heavy drinking – so moderation does matter. The type of alcohol could matter too as one study found hard liquor to have more negative effects on sleep than drinks with a lower alcohol content.
The nocturnal impacts of alcohol are not without consequences for how we feel the next day. Since sleep plays an important role in the restoration and enhancement of energy levels and intellectual functions, it is not so surprising that drinking before sleep has been shown to engender fatigue and memory decrements the next day.
Overall, although we may not notice it, alcohol drives pulling and pushing forces that dynamically change across the night. The net result? We cannot say that the glass is half-full and half-empty: Alcohol negatively affects sleep. Staying aware of this is key to having realistic expectations and a balanced viewpoint on the relationship between alcohol and sleep. What is certain though: Using alcohol to improve your sleep is not a viable strategy.
Dr. Rébecca Robillard, PhD, is a clinical neuropsychologist and associate professor at the School of Psychology at the University of Ottawa. She also leads clinical sleep research at the Royal mental health hospital. She co-chairs the Canadian Sleep Research Consortium, a national hub of sleep scientists and clinicians.