MONDAY, Aug. 15, 2011 (HealthDay News) -- You might want to take a pass on that nightcap, a new study suggests.
Japanese researchers report that alcohol hinders the restorative functions of sleep.
The findings, from a study of 10 male university students, appear online and in the November print issue of the journal Alcoholism: Clinical & Experimental Research.
Booze's effect on sleep appears linked to a disruption in nervous system function.
Normally, as people sleep through the night, "the parasympathetic nervous system, responsible for 'rest-and-digest' activities, is dominant over the sympathetic nervous system, responsible for stimulating activities," Yohei Sagawa, a physician in the department of neuropsychiatry at the Akita University School of Medicine, explained in a journal news release. "We wanted to investigate how alcohol may change this complementary relationship."
To do so, Sagawa and his colleagues gave study volunteers different levels of alcohol -- 0 grams (control group), 0.5 grams (low dose), and 1.0 grams (high dose) -- before the participants went to bed on three separate occasions.
Using electrocardiograms, the researchers then focused on the relationship between the volunteers' heart rate variability and their sleep. The team found that alcohol increased heart rate and interfered with the restorative functions of sleep -- and the more alcohol the participants drank, the greater the effect.
"Although the first half of sleep after alcohol intake looks good on the EEG, the result of the assessment regarding the autonomic nerve system shows that drinking leads to insomnia rather than good sleep," Sagawa said.
The effect on habitual drinkers might be even worse, a study co-author said.
"The current study evaluates the acute effects after only a single dose of alcohol intake, and subsequently found a negative health consequence," Seiji Nishino, director of the Sleep & Circadian Neurobiology Laboratory at Stanford University School of Medicine in La Jolla, Calif., said in the news release. "Many subjects habitually drink alcohol, and if the reduction of parasympathetic nerve activity during sleep chronically occurred, negative health consequences may be much larger and may induce various diseases."
"It is generally believed that having a nightcap may aid sleep, especially sleep initiation," Nishino added. "This may be true for some people who have small amounts of alcohol intake. However, it should be noted that large amounts of alcohol intake interfere with sleep quality and the restorative role of sleep."
The U.S. Centers for Disease Control and Prevention has more about sleep and sleep disorders.