Insomnia sufferers need not forego coffee completelyA new study from Henry Ford Hospital shows that caffeine ingested 6 hours before bedtime has a disruptive effect on sleep and can cause insomnia.

For goodness sake, tell me something I don’t already know! Drinking coffee late in the day has always been a surefire summons to insomnia at my house.

But there’s a lot about caffeine I didn’t know—and that you might not know either—so I thought I’d pass along a few fascinating factoids.

Who’s Sensitive, Who’s Not

When it comes to caffeine sensitivity, it’s all in the genes. Swiss researchers in 2007 published a paper linking self-rated caffeine sensitivity to differences in a particular adenosine receptor gene (adenosine is a neurochemical whose action is blocked by caffeine). The upshot is that some people can drink coffee after dinner with impunity; others can’t.

In 2012, Stanford researchers found that sensitivity to caffeine is also linked to chronotype—whether you’re a morning person or an evening person. In this study, caffeine had a strongly disruptive effect on the sleep of morning types, a moderately disruptive effect on the sleep of intermediate types, and virtually no effect at all on the sleep of night owls.

Does Caffeine Sensitivity Increase with Age?

Yes. In a paper published in April 2013, a group of Australian pharmacologists found that by the age of 65 or 70, adults experience a 33 percent decrease in the rate at which caffeine is metabolized and cleared from our bodies. This has practical implications for caffeine-sensitive baby boomers.

On average, caffeine has an elimination half-life of 5 to 6 hours. So 5 or 6 hours after you drink a cup of coffee, the amount of caffeine in your blood will have decreased by half. But as we age, our bodies take longer to clear most drugs, and caffeine is no exception. While at 35 we might have gotten away with an espresso at 3 p.m., at 55 we may need to fix the caffeine cut-off time just after lunch.

Beyond Timing

The other important factor to take into account is the amount of caffeine in your beverage of choice. You may be surprised at the caffeine content of some of these drinks:

Starbucks Venti 20 oz. 415 mg
Folgers Classic Roast Instant Coffee 12 oz. 148 mg
McDonald’s Coffee, large 16 oz. 133 mg
Black tea, brewed 3 minutes 8 oz. 30-80 mg
Snapple Lemon Tea 16 oz. 62 mg
Green tea, brewed 3 minutes 8 oz. 35-60 mg
Pepsi 12 oz. 38 mg
Coca-Cola, Coke Zero, or Diet Pepsi 12 oz. 35 mg
Jolt Energy Drink 23.5 oz. 280 mg
Red Bull 8.4 oz. 80 mg
Starbucks Hot Chocolate 16 oz. 25 mg

For a complete list of caffeinated beverages and the buzz they deliver, visit the Center for Science in the Public Interest.

Does caffeine affect your sleep? How? What’s your daily cut-off time?

Posted by Lois Maharg, The Savvy Insomniac

Lois Maharg has worked with language for many years. She taught ESL, coauthored two textbooks, and then became a reporter, writing about health, education, government, Latino affairs, and food. Her lifelong struggle with insomnia and interest in investigative reporting motivated her to write a book, The Savvy Insomniac: A Personal Journey through Science to Better Sleep. She now freelances as an editor and copy writer at On the Mark Editing.

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