That’s all very well in theory but in practice, many of us haven’t been able to stick with the same bedtime since school. If you’re getting a good amount of sleep or a shorter but deeper snooze, that surely doesn’t matter… right?

Wrong. Dr Guy Meadows, co-founder and clinical lead at Sleep School tells Stylist that “keeping an irregular sleep schedule confuses our body clock, which can lead to a condition known as social jet lag. Like regular jet lag, it can cause insomnia, fatigue, nausea and brain fog.”

Dr Lee says that sleep regularity is a ‘vital’ component of sleep quality, even if quality is “probably more important than sleep quantity”. She points to a 2021 review of sleep studies which concluded much the same thing while flagging the fact that while measuring sleep quantity is relatively easy, there are no agreed standards for classifying sleep quality.

Saying that, we can assess poor sleep. Dr Lee says: “Sleep disturbances, such as difficulty falling asleep and waking at night are linked to high blood pressure and raised cholesterol levels. In a 2020 Japanese study of nearly 2 million adults, the risk of cardiovascular disease – angina, heart attacks, heart failure and atrial fibrillation – were all significantly lower in those who reported restful sleep. Improving sleep quality should be a priority in the management of those with established cardiovascular disease.

Sleep regularity: does it really matter if we don’t go to bed at the same time every night?