00:00-02:59

Body enters shutdown

Sleep hormone melatonin peaking

Minimum levels of attention and vigilance

Brain washes itself and consolidates memories

It is well and truly bedtime. Hormonal changes in the body say it is time to be asleep. The brain is washing away the waste toxins built up during a hard day's thinking and the bowels are shut down for the night. If you're still awake be careful, levels of attention are at their lowest, making industrial accidents a risk on night shifts.

03:00-05:59

Body fast asleep

Minimum core body temperature

Severe asthma attacks more common

Most natural births occur

It's the heart of the night and your body is still some way off waking up and getting you out of bed. Sleep hormone melatonin levels are still high, but glide down as dawn approaches. Your core body temperature is notably cooler than any other part of the day as energy is diverted elsewhere, such as skin repair.

06:00-08:59

Heart attack danger zone

Good time to wake up

Heart attacks more likely

Men have their testosterone peak

Be careful - this is the time of day your heart is most vulnerable. Blood vessels are stiffer and more rigid, the blood is thicker and stickier and your blood pressure is at its peak. It all adds up to the greatest risk of a heart attack you'll face today. Your body is kicking into gear as sleep hormone melatonin production stops. It is a poor time to exercise.

09:00-11:59

Mind most alert

Maximum cortisol levels

Maximum alertness

Best short-term memory

You're probably in work and it's time to get some of the heavy thinking done. The stress hormone cortisol reaches its natural peak giving our brains a boost of alertness. We tend to be most productive before lunch and tests show short-term memory is at its best. Stay busy, there's a big dip coming up.

12:00-14:59

Biological siesta

Increased gastric activity

Post lunchtime dip in alertness

Surge in road deaths

With a lunchtime belly full of food, there's a boost in gastric activity. But this soon adds to the 'biological siesta' as alertness dips and affects driving ability. There's a noticeable rise in the number of deaths on the roads from 14:00, particularly in older people. It's also a bad time to drink alcohol as it can make you more drowsy than at other times of the day.

15:00-17:59

Go exercise!

Best lung & cardiovascular performance

Core body temperature rising to its peak

Good time to exercise

Go get a sweat on! Body temperature increases in the late afternoon like a natural warm-up, the heart and lungs work better and muscles are 6% stronger than at their lowest point in the day. Some people have even tried using this 'athletic sweetspot' to increase their chances of breaking sporting world records.

18:00-20:59

Watch what you eat

Poor time to eat a big meal

Liver handles alcohol better

Intuitive thinking is better

Ready for dinner and maybe a drink? Well you might not want to leave it too late. Emerging evidence suggests the body changes the way it handles food as it gets closer to night-time. Eating big meals in the evening could increase the risk of obesity and diabetes. The liver is more able to deal with alcohol if you fancy a tipple.

21:00-23:59

Getting ready for sleep

Melatonin production building

Core body temperature dropping

Good time to go to sleep

Bedtime is fast approaching and the pineal gland in the brain is churning out the hormone melatonin to help you nod off. Core body temperature is falling and the internal body clock is saying it's time to swap the sofa for the duvet. It'll happen first if you're a morning or 'lark' type person, before hitting the 'owls' a bit later.

Take the Quiz

Are you a lark or an owl?

People often describe themselves as a "morning person" or an "evening person" depending on when they feel their best. Of these five groups, see which description suits you best. Extreme larks are the ultimate early bird - up and out of the door while others are struggling with the snooze button on their alarm clock. But they pay for it in the evening when they nod off early. Larks also prefer mornings. They are out of bed early and greet the new day with cheer and a smile while everyone else is grumpy, bleary-eyed and hugging a mug of coffee. Some people function only in the morning, while others hit their stride well after the sun has set, but the Balanced group is somewhere in the middle. It's a good place to be - the best of both worlds. Owls are no strangers to burning the midnight oil and love a late night. However, mornings are a struggle. Extreme Owls - no-one can power through the night quite like them. 4am? No sweat! But early starts must fill them with dread and they've probably worn out the snooze button on the alarm clock too.

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Body Clock Quiz

Are you a morning or evening person? This questionnaire helps you work out if you are a lark or an owl, or whether you have a more balanced body clock.

1.What time would you get up if you were entirely free to plan your day?

2.During the first half hour after having woken in the morning, how tired do you feel?

3.At what time in the evening do you feel tired and, as a result, in need of sleep?

4.At what time of day do you think that you reach your “feeling best” peak?

5.Which one of these types do you consider yourself to be?

Extreme Lark

Extreme Lark

Lark

Lark

Balanced

Balanced

Owl

Owl

Extreme Owl

Extreme Owl