Study results may be good news for coffee lovers, bad news for smokers.

Trouble sleeping? You aren't alone. Studies estimate that up to 20% of people have a sleep disorder, let alone just having a bad night’s sleep.

So what can we do to get a better night’s sleep? Cut back the coffees? Relax with a wine, beer & cigarette before bed?

Um. How about the opposite???

A recent study, one of the largest longitudinal studies to date, has shed some light on how our evening consumption of our favourite vices - caffeine, alcohol, and nicotine - play a role in our sleep troubles.

And it’s a little surprising……

Researchers from Florida Atlantic University studied 785 people for 5,164 days using actigraphy (wrist-watch-like sensors) and daily sleep diaries to record their sleep and how much alcohol, caffeine and nicotine they consumed within four hours of bedtime.

How Does Caffeine Affect Sleep?

The study found:

• Consuming caffeine within four hours of bedtime did not affect any of the sleep parameters (individual variations in caffeine sensitivity were not tracked);

How Does Alcohol Affect Sleep?

• Alcohol within four hours of bedtime hurt sleep continuity compared to a night without alcohol (even after controlling for age, gender, obesity, level of education, having work/school the next day, and depressive symptoms, anxiety, and stress);

How Does Nicotine Affect Sleep?

• Nicotine within four hours of bedtime worsened sleep continuity compared to a night without nicotine (even after controlling for age, gender, obesity, level of education, having work/school the next day, and depressive symptoms, anxiety, and stress);

• Nicotine was the substance most strongly associated with sleep disruption;

• Nicotine was the substance most likely to be used by those self-reporting as insomnia sufferers;

• Evening nicotine use significantly impacted insomnia, shortening sleep duration by an average of 43 minutes.

The results from this study are especially important as none of the people studied were selected because they had sleep problems. In fact, they generally had high sleep efficiency.

Okay, so what’s the takeaway? If you want sleep with less disruption, avoid alcohol and especially avoid nicotine within four hours of bedtime (the study didn’t look at the effects of taking these substances prior to four hours before bedtime, however other evidence suggests they are likely to disrupt sleep when taken in the evening at all).

We’ve written before about how even mild sleep loss can impact next day mood and brain function so reducing sleep disruptors is a smart move if you want to sleep better and feel better.

But what about the caffeine? Does this mean you can start smashing the coffees before bed? Not so fast.

Caffeine affects everyone differently. So if experience tells you that caffeine keeps you awake (caffeine blocks the effect of adenosine on the brain - read here about adenosine and sleep) our suggestion is to have your last coffee just after lunch for a better night’s sleep (and watch the total amount of caffeine you consume).

The study was published in the journal Sleep (Spadola et al., 2019).