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.
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.
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."