They have a saying in the American south "it should be as black as night, as hot as hell and as strong as love" and they're of course talking about coffee.
Many millions of us are addicted to the caffeine hit coffee provides and drink it day and night. So if we drink coffee at night does it keep us awake?
Now, your first instinct is probably to say yes … but many coffee lovers will tell you it doesn't affect their sleep at all. So maybe we're blaming coffee, when other factors are at play?
Our reporter Leila McKinnon lies down on the job to find out.
To find out the truth, Leila's visiting the Henry Ford Sleep Disorders Centre in Detroit. The centre's director is Professor Timothy Roehrs. He's been working on sleep for 20-plus years so how have things changed over time? Are we getting less sleep?
"As a society that's most definitely true. Sleep time was approximately 7.5 hours in the population, now it's more like 7.2 or 7.1 hours," says the Professor.
The reasons? More shift work, longer hours, we've put on weight, which can disturb sleep, and we're taking drugs which disrupt sleep patterns … but is the late night coffee one of those?
It's time to find out.
"We're going to ask you [Leila] to sleep here two nights and on one night we're going to actually give you a caffeinated beverage and on another night we're going to give you a decaffeinated beverage. Then after you've awakened in the morning, we'll score up the sleep and we'll compare the two nights," says Professor Roehrs.
Simple enough: one night with caffeine, one night without but Leila won't know which.
Time to get ready for bed. Technician Rhonda applies sensors to Leila's face and scalp they monitor sleep indicators like breathing and movement. The information is then fed back to a central computer which records how deep Leila's sleep is and if she wakes throughout the night, even if it's just for a few seconds.
The centre makes Leila a cup of decaffeinated instant coffee. For accuracy, the caffeine dose will be added in separately on one night. But which one?
This is one of the worst coffees that I have ever had. I'm not sure whether it's got caffeine in it or not but that's all part of the experiment," says Leila.
When Leila is tucked up into bed and heads off to sleep, the machines go to work.
It's the morning after the night before.
Leila: "Well I think that went okay. It was a very different experience I slept okay don't know whether I had the caffeine or decaf but I'll be back here tonight and we'll find out."
Professor Roehrs knows better than Leila does how well she slept he's got data tracking every minute. He won't tell Leila the results just yet but if anyone knows the importance of a good night's sleep, it's him.
If I were to take and reduce your sleep time by an hour, the next day I could measure that you'd be more sleepy, fatigued, less ability to attend, less ability to think and remember and more likely to even get into an automobile accident if you were driving long distance," he says.
As Leila heads into her second night of our experiment everything's the same, except the coffee. It's still awful but is it caffeinated or decaf?
The next morning…
Professor Roehrs asks Leila how she slept last night?
"Good, thank you. I think the second night was maybe a bit better I don't know."
Leila may be surprised they head back down to the professor's office to take a look at Leila's tracings for the two nights.
So which night does Leila think she had the caffeine?
"I would be pretty sure I had it on the first night, I had a much better sleep last night."
Well, she's right.
That late-night coffee made a big difference to Leila's sleep. On night one the caffeine night it took Leila 50 minutes to fall asleep but only 16 minutes on the decaf night. Her REM sleep, that's the phase when you dream, should be between 20 and 25 percent, but on the caffeinated night she had a total of 19 percent. The next night, without caffeine, she had 26 percent.
So one cup off coffee just before you go to bed can make that difference.
"That's very true, but in this study we actually gave you the equivalent of two cups of coffee we gave you 250 mg. I had the report that you normally consume about 200mg of caffeine so I wanted to make sure I had a dose of coffee sufficient to affect your sleep," says Professor Roehrs to Leila.
So he doubled Leila's dose, to make sure she felt the effects, because even light drinkers develop caffeine tolerance and that tolerance is why big coffee drinkers don't think they feel the effects of that last cup at night. But chances are their sleep is disrupted.
Leila didn't know it, but she woke up 27 times, and in all, she lost a whole hour of sleep on the caffeine night. The solution? Professor Roehrs says one caffeine hit can last up to five hours in the body. So for a good night's sleep you do need to lay off the caffeine well before bed.
Consider changing that last drink to tea it has got caffeine in it, but in tea its effects are counteracted by a chemical called L-theanine.
But if it must be coffee, try to gradually cut down, because it is effecting your sleep, whether you know it or not.
So coffee before bed is bad news, but you don't have to give up the habit, just aim to drink your coffee early in the day so by the time it comes to get some shut eye you'll be well and truly ready.
- Other health effects of coffee are just starting to come to light and the good news is, it's good news! Coffee drinkers are 80 percent less likely to develop Parkinson's disease; two cups a day may cut your chances of getting colon cancer by 25 percent; and the brew stops the development of cirrhosis of the liver in up to 80 percent of patients.
- Are you one of the people who just can't function in the morning 'til you've had your caffeine fix? Why is that? Because you're addicted. Your body goes into a withdrawal state during sleep so you need coffee when you wake up to counteract it.