How the WHEN of Drinking Alcohol Affects Intoxication

How the WHEN of drinking alcohol affects intoxication

I get asked about alcohol’s effects on sleep A LOT, and never more than around the holidays. It makes sense, of course. It’s this time of year when people drink more often, consume more alcohol than is their norm—and likely drink at different times of day than they typically do. I’m thinking about Christmas Day brunch mimosas, and beers watching bowl games on New Year’s Day. Heck, this year, your holiday calendar might be filled with Zoom calls where you’re raising a glass or two in the afternoons.

We’re rounding out this holiday stretch, and I want to tell you about brand-new research on the circadian effects of alcohol—how the timing of your alcohol consumption influences how alcohol is processed in your body, and what that means for intoxication and impairment.

This new research provides new, important details about the impact of the timing of alcohol intake on breath alcohol concentration. That’s the measurement of intoxication that’s taken by breathalyzer tests. This new research has determined that breath alcohol concentration, or BrAC, follow a circadian rhythm. At different times of day and night, the same amount of alcohol has a different impact on breath alcohol levels.

What is BrAC?

Before we jump into the study results and what they mean, here’s a quick lesson on breath alcohol concentration.

BrAC is, as I’ve said, measured by a breath test, most commonly a breathalyzer. When we drink alcohol, it is absorbed into the bloodstream. As blood moves through the lungs to deliver oxygen, alcohol transfers from the blood to the breath—it actually evaporates from the blood as lungs work to breathe. Breathalyzers sense the alcohol content in breath, and then analyze and convert that information to a measurement of blood alcohol concentration (aka blood alcohol content). It’s blood alcohol content, or BAC, that state and federal governments use to assess a driver’s level of impairment, and whether drivers are too intoxicated to drive legally. The US federal limit for BAC is 0.08%. States have their own BAC levels (none exceed 0.08%), and states set individual limits for underage drivers and for enhanced penalties for very impaired drivers.

Until now, the impact of circadian rhythms on breath alcohol concentration has been unclear, so this is some new detail in how our circadian system affects the way the body processes alcohol. That’s important every day of the year, but especially relevant at this time of year when people tend to drink more and at different times of day.

The circadian timing of breath alcohol

This new research, published this month in the journal Sleep, was conducted by scientists in Singapore, who investigated several questions about how our circadian system might affect breath alcohol levels, including whether circadian rhythms change:

  • How long it takes for BrAC to reach its peak
  • How high BrAC levels reach at their peak
  • How long it takes for BrAC levels to fall back to zero

The study included 20 young adults, between the ages 21-30. Over a period of 40 hours in a laboratory setting, participants were given the same dose of alcohol every 4 hours, and had their breath alcohol measured every 5 minutes with a breathalyzer.

What did these scientists find?

A significant circadian rhythm affecting the amount of alcohol in the breath. In particular, they found two aspects of breath alcohol levels affected by circadian timing:

Peak BrAC levels

Researchers found that at different times of the day, breath alcohol levels reached higher peaks—from consumption of the same amount of alcohol over the same period of time.

The highest peak BrAC levels occurred in the morning and afternoon.

The lowest peak BrAC levels happened in the evening hours, near to the time when the daily core body temperature rhythm was at its highest (that’s around 6-8 p.m.) and as daily cortisol rhythm was dropping to its lowest levels. Peak BrAC levels began to rise again overnight before reaching their daily highs in the morning and afternoon hours.

What does this mean? Compared to evening alcohol consumption, drinking during the day results in a higher concentration of alcohol in the breath, even if you’re drinking the same amount and at the same pace. This makes sense, since we know that the peak timing of the enzyme to digest alcohol ( alcohol dehydrogenase) is often in the later afternoon or early evening ( for all chronotypes).

Time it takes BrAC to zero out

Researchers also found a circadian rhythm attached to the time it takes alcohol to clear completely from the breath. Again, daytime hours were in the spotlight. The time it took breath alcohol concentration to return to zero after drinking was longest in the late morning and in the afternoon.

This is some new detail about the impact of the timing of alcohol consumption on breath alcohol, and on measurements of intoxication and impairment. But other scientific research has already established that there is a circadian influence over alcohol in the body.

We know that the body metabolizes alcohol differently at different times of day, and that we feel the effects of alcohol differently, depending on when we drink.

The body is most effective at metabolizing alcohol in the early to mid-evening hours. And our bodies are least adept at metabolizing alcohol in the morning.

The sedating effects of alcohol are stronger during the daytime. If you drink in the morning or the afternoon, you’ll feel sleepier, and less alert. And as we now see from this latest research, there is a higher concentration of alcohol present in your breath, that will take longer to diminish and disappear.

This previous research lines up pretty strongly with these new findings. The takeaway? Evening hours are when the body is best equipped to process alcohol, and daytime is when your body is least equipped to do so.

There’s also some fascinating new research showing that our preferences for alcohol follow a daily circadian rhythm, and that individual chronotypes have different times of day when cravings for alcohol are the strongest. Late chronotypes (the Wolves of the world) reach their peak craving for alcohol later in the day than early chronotypes (aka Lions).

Alcohol disrupts the circadian system

Circadian timing affects how well and quickly the body processes alcohol, and also how much of an impact alcohol has on our alertness. We also know that alcohol itself can disrupt healthy circadian timing.

Alcohol directly interferes with the ability of the master biological clock to synchronize itself, making it less responsive to the light cues that keep it in sync. Even low levels of routine alcohol consumption can be disruptive to healthy circadian rhythms—and that can have a widespread impact on sleep and health.

Alcohol is highly effective at suppressing melatonin, a key circadian regulator of sleep-wake cycles. Studies show a moderate dose of alcohol up to an hour before bedtime can reduce melatonin production by nearly 20%.

In addition to problems with sleep, we’re learning more all the time about how alcohol’s circadian disrupting effects may create problems for physical and mental health, including:

Poor liver function. The liver acts as a filtering system for the body, helping metabolize food and chemicals (including alcohol itself), and pulling toxins from the bloodstream. Like nearly all of the body’s organs, the liver operates with a daily circadian rhythm. Alcohol interferes with these circadian rhythms regulating the liver, and can contribute to compromised liver function, liver toxicity and disease. 

Leaky gut. The gut microbiome–our second brainexerts strong signals that affect circadian function throughout the body.   Circadian rhythms thrown out of sync by alcohol can weaken the lining of the gastrointestinal tract, making it more vulnerable to permeation—that’s the leakiness that allows bacteria, toxins, and food to leave the intestines and enter the bloodstream.

Depression. There’s a complicated relationship among depression, alcohol and sleep. People suffering from depression may already have disrupted circadian rhythms, and the presence of even moderate amounts of alcohol may push those rhythms further out of sync.

Other effects of alcohol on sleep

In addition to disrupting circadian clocks and our daily circadian rhythms and sleep-wake cycles,  alcohol interferes with the body’s internal sleep drive. Alcohol elevates levels of adenosine, a chemical that regulates sleep by rising naturally in the body the longer you’ve been awake, and increasingly blocking other chemicals that stimulate wakefulness. Alcohol’s adenosine-boosting effects make you sleep at times other than you would be naturally, and can throw your natural sleep-wake cycle off course.

And alcohol contributes to more restless, less refreshing sleep. A recent study showed that as little as a single drink has a negative effect on sleep quality. This study found that moderate alcohol consumption reduced sleep quality by 24%, and high alcohol consumption lowered sleep quality by more than 39%.

As you move through the holidays, you can enjoy drinking and protect your sleep. Remember these basics:

Moderation—of course. Heavy drinking not only leads to greater impairment (and risks to you and others), but also sabotages restful sleep. If you want to forgo alcohol this holiday season, or just take an occasional break from alcoholic drinks, here are a few non-alcoholic drinks that will actually boost your sleep!

Timing matters too. To avoid the sleep and circadian-rhythm disrupting effects of alcohol at night, I recommend stopping drinking 3 hours before bed, to let your body fully process alcohol and its effects before your nightly rest.

And as you’re enjoying holiday time, keep in mind, as this latest scientific research shows us, there are optimal—and suboptimal—times for your body to handle the alcohol you’re enjoying. Drinking during the day will affect your body more strongly, with a greater measurable presence of alcohol that takes longer to disappear. Use sound judgment, stay safe, and happy holidays to you!

Sweet Dreams,

Michael J. Breus, PhD, DABSM

The Sleep Doctor™

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Michael Breus, Ph.D - The Sleep Doctor is a Diplomate of the American Board of Sleep Medicine and a Fellow of The American Academy of Sleep Medicine and one of only 168 psychologists to pass the Sleep Medical Specialty Board without going to medical school. Dr. Breus is a sought after lecturer and his knowledge is shared daily in major national media worldwide including Today, Dr. Oz, Oprah, and for fourteen years as the sleep expert on WebMD. Dr. Breus is the bestselling author of The Power of When, The Sleep Doctor’s Diet Plan and Good Night!

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