Does the "When" of Alcohol Impact Intoxication?

Here's how the timing of your drinking can affect your intoxication levels.

Posted Dec 31, 2020

Will Stewart/Unsplash
Source: Will Stewart/Unsplash

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 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, follows a circadian rhythmAt 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 the lungs work on breathing. Breathalyzers sense the alcohol content in the breath and then analyze and convert that information to a measurement of blood alcohol concentration (aka blood alcohol content).

It is 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 U.S. federal limit for BAC is 0.08 percent. States have their own BAC levels (none exceed 0.08 percent) and set individual limits for underage drivers and enhanced penalties for very impaired drivers.

Until now, the impact of circadian rhythms on breath alcohol concentration has been unclear, so this research offers some new details on how our circadian system affects the way the body processes alcohol. 

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 when at their peak
  • How long it takes for BrAC levels to fall back to zero

The study included 20 young adults between the ages of 21 and 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 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.

The 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. 

We know that the body metabolizes alcohol differently at different times of the 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.

There’s also some fascinating new research showing that our preferences for alcohol follow a daily circadian rhythm, and individual chronotypes have different times of day when cravings for alcohol are the strongest. 

Alcohol disrupts the circadian system

Circadian timing affects how well and quickly the body processes alcohol, and also how much 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 percent.

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: 

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.

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 percent, and high alcohol consumption lowered sleep quality by more than 39 percent.

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. 

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, Ph.D., DABSM

The Sleep Doctor™