How does alcohol affect your sleep?

A new study assesses the effect of alcohol consumption on the restorative quality of sleep. The findings might make you want to change your drinking — and implicitly, your sleeping — habits.

That extra glass of wine could make your sleep less restful and regenerative.

The negative health consequences of alcohol are numerous. From more alarming outcomes such as cancer to more "cosmetic" inconveniences such as premature signs of aging, alcoholic beverages seem to hide a range of toxic effects that can slowly take a toll on our health.

Most of us probably think that unless someone has alcohol dependency or drinks heavily, they're out of alcohol's negative reach. But more and more studies are pointing to a different conclusion.

A recent study reported by Medical News Today, for example, suggested that just one drink can shorten our lifespan. The jury's still out on whether drinking in moderation is good for you, but some studies have suggested that even light drinkers are at risk of cancer due to their alcohol intake.

A new study, carried out by Finnish-based researchers, adds to these dire prospects. Julia Pietilä, a researcher at the Faculty of Biomedical Sciences and Engineering at Tampere University of Technology in Finland, is the first author of the paper, which was published in the journal JMIR Mental Health.

Studying alcohol and sleep quality

The fact that the study used real-life information makes it unique. Pietilä and colleagues examined data from 4,098 men and women aged between 18 and 65, whose heart rate variability (HRV) was recorded in uncontrolled, real-world conditions using a special device.

As the authors write, "The association between acute alcohol intake and physiological changes has not yet been studied in noncontrolled real-world settings."

The scientists had access to sleep HRV recordings from a minimum of 2 nights: one where the participants had consumed alcohol and one where they hadn't.

HRV measures the variations in time between heartbeats, variations which are regulated by the autonomic nervous system.

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The autonomic nervous system comprises the sympathetic nervous system and the parasympathetic nervous system. The former controls the fight-or-flight response, whereas the latter is responsible for the "rest-and-digest" state.

Therefore, HRV measurements enabled the researchers to assess the quality of the participants' restful state. The scientists examined the participants' first 3 hours of sleep after drinking alcohol.

Alcohol intake was broken down into "low," "moderate," and "high," — categories that were calculated based on the participants' body weight.

The Dietary Guidelines for Americans define moderate drinking as up to one drink per day for women, and up to two daily drinks for men.

Even low, moderate drinking impairs sleep

The study revealed that alcohol reduced the restorative quality of sleep. Specifically, a low alcohol intake decreased the physiological recovery that sleep normally provides by 9.3 percent.

Even as little as one drink was shown to impair sleep quality. Moderate alcohol consumption lowered restorative sleep quality by 24 percent, and high alcohol intake by as much as 39.2 percent.

These results were similar for men and women, and alcohol consumption affected sedentary and active people alike.

Interestingly, the harmful effects of alcohol were more pronounced among young people compared with seniors.

Study co-author Tero Myllymäki, a professor in the department of Sports Technology and Exercise Physiology at the University of Jyväskylä in Finland, comments on the findings, saying "When you're physically active, or younger, it's easy, natural even, to feel like you're invincible."

"However, the evidence shows that despite being young and active you're still susceptible to the negative effects of alcohol on recovery when you are asleep."

"It's hard to overstate the importance of sleep, in terms of both quality and quantity," adds Myllymäki.

"While we may not always be able to add hours to our sleep time, with insight into how our behaviors influence the restorative quality of our sleep we can learn to sleep more efficiently. A small change, as long as it's the right one, can have a big impact."