We all know whether we're a morning or an evening person. Some of us prefer to get up early, whereas others like to stay up late into the night.
If you and your partner live together and you are at opposite ends of the scale, you might find some clashes in your routines.
To some extent our body clock — or chronotype — is determined by our environment, such as how much light we're exposed to. But what you might not know is there are physiological and biological differences to the two body clock types, and you have a genetic predisposition to one of them.
In other words, you and your partner may behave differently because you're wired that way.
These differences are clear in the levels of the two hormones involved in regulating sleep. Melatonin rises in the evening and helps prepare our bodies for sleep, whereas cortisol rises in the morning and helps us to wake up. For night owls, melatonin increases later in the day, while cortisol rises earlier in morning people.
From these biological differences our different habits and routines arise. This is fine if you live alone and you've worked out your own rhythm, but research has shown that if two people live together and their "sleep habits" don't match, conflicts can arise in their relationship.
There are well-known sleeping problems such as snoring and insomnia, which can keep one partner up late into the night, making them function poorly the next day and having a negative impact on their mood. But routine clashes can also be a problem. For example, if you're in bed by 10 p.m. and your partner comes in and wakes you up four hours later, or if you've had a late night and you get disturbed early in the morning by the radio and hairdryer.
Night owl/early bird relationships may not be destined to fail
According to sleep scientist Elise Facer-Childs, a Doctoral Researcher at the University of Birmingham, having a partner with a different chronotype to you isn't necessarily a disaster.
"I'd say there's two different ways you could look at it," she told Business Insider. "[Saying] 'We're different chronotypes so let's try and shift so we can be the same,' and maybe there'd be benefits to that, but on the other side of things, saying 'We're different chronotypes, but let's use that to our advantage.'"
For example, research often focuses on sleep, and the benefits of getting enough consistent hours of it to be healthy. However, what isn't so well researched is how it can be beneficial to be up at different times of the day.
"In terms of something like childcare or parenthood, you could definitely use something like different chronotypes as an advantage," said Facer-Childs. "If one parent much preferred the evening, and likes getting up later, and the other one much prefers the morning, you could see how that could really work."
Instead of battling over whose turn it is to get up in the morning, two people could be better suited to getting the kids up or feeding the baby at night depending on how their body clocks work.
On the other hand, studies have shown that sleeping alone can be better for you. However, there's a psychological impact if you and your partner choose to sleep separately.
"You don't associate sleeping in separate rooms as something good," Facer-Childs said. "So there's a weigh up between people actually preferring to sleep with their partner, even if it means their sleep is of poorer quality."
It's more or less common sense to try and be a bit quieter in the morning if your partner is still asleep, or avoid don't turning bright lights on if you come to bed later than them. However, as sleep seems to be something we take for granted, it might not be so obvious.
Facer-Childs said it's also important to work out whether the sleep is affecting the relationship or the other way around. Anxiety and stress can be linked to sleep disturbances, and sometimes these can be amplified when you're in a bad relationship. In those cases, it's something that needs to be looked at from the psychological perspective, as opposed to analyzing the sleep.
Like everything in a relationship, it's about balance
As for the perfect chronotype match, there is no such thing. Facer-Childs says it's not a disaster if you are the same chronotype and it's not a disaster if you're opposites.
"It's probably unrealistic to find your perfect chronotype because everything is a balance in a relationship," she said. "Just like you don't expect to find somebody that follows exactly the same working schedule, or has the same hobbies, we can't necessarily expect someone to have exactly the same sleeping patterns as us."
What's important, though, is talking and being open about it with your partner. If you hate their schedule, say so, and you can probably work something out. Just don't brush it off as a minor issue, because sleep is vital to our health.
"Sleep is extremely important and we do see it as a bit of a luxury in this day and age I think," Facer-Childs said. "The whole 'I'll sleep when I'm dead' motto. It's more like you don't sleep and you will be dead."
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