Body Clock: Six things we learned
The BBC Day of the Body Clock explored 24 hours of the human body clock through 24 hours of BBC News.
Even the most dedicated and sleep-deprived of us could not catch it all, so what did we learn?
If you need an alarm clock, you need more sleep
The day started with doctors warning that we have become "supremely arrogant" about the amount of sleep we need.
So how do you know if you're getting enough?
"If you need an alarm clock to wake up or are reliant on caffeinated drinks in the morning you need more sleep," says Prof Russell Foster from the University of Oxford.
He says getting too little sleep also makes us irritable and impulsive, and other warning signs include taking risks while driving and just being more tetchy than usual.
Prof Russell Foster said people need to "look at lives and take a bit of control".
Olympic swimmers don't like mornings
Physical strength fluctuates throughout the day.
In the afternoon, muscles are up to 6% stronger than at their weakest point in the day. The heart and lungs work better in the afternoon and your core body temperature is higher acting as a natural warm-up.
Swimmer and Olympic bronze-medallist Steve Parry told BBC Radio 5 live: "That's why professional athletes do their competing in the evening because we know they perform better at that time of day, I won my Olympic medal at this time.
"We would do our hard sets training for the Olympics - the majority of them were done late in the afternoon because that's when your body is ready to perform, we wouldn't think about doing that stuff really early in the morning.
"In Beijing because the Americans get their way on these things and NBC pays so much money for the rights the finals actually switched to the morning and we did see a lot of the swimmers going slower in terms of the times they were able to do."
When you take drugs matters
The body clock changes the way we function during the day, including the way our bodies respond to drugs.
The field of chronotherapy is aligning medical treatment to our circadian rhythms.
Flu jabs may be better in the mornings, statins are best taken before bed and the symptoms of arthritis are worst in the morning, so doctors are trying to target the symptoms then.
Prof Francis Levi, who is pioneering the use of the body clock in cancer treatment, said: "We have clocks within our cells that govern the metabolism of drugs. So some drugs are best given at night and others during the day.
"We have found chronotherapy is reducing the toxicity of treatments and improving the quality of life of patients, by respecting the circadian rhythms of the patients.
Late meals make you fat
We all know that the number of calories we eat can affect our waistlines, but the time we choose to eat them matters too.
Just as the body's response to drugs changes through the day, so too does its response to food.
It is harder to deal with fats and sugars late in the evening, which can increase the risk of obesity and type-2 diabetes. It is a particular problem for shift workers.
Dr Victoria Revell, from the University of Surrey, told the BBC News Channel: "We know that our metabolism changes across the day and that earlier in the day our body will find it easier to metabolise heavier meals.
"For people who eat late at night the body will find it harder to metabolise those meals and that will have an effect on our health."
Blue light is keeping you awake
The body clock uses light to work out the beginning of the day and bright light in the evening can keep us awake.
Smartphones, tablets, computers and LED lights contain at lot of blue light, which is "right in the sweet spot" for disrupting the body clock.
Prof Charles Czeisler, from Harvard Medical School, said: "Light exposure, especially short wavelength blue-ish light in the evening, will reset our circadian rhythms to a later hour, postponing the release of the sleep-promoting hormone melatonin and making it more difficult for us to get up in the morning.
And when does Evan go to bed?
The presenters of BBC Radio 4's Today took part in an experiment to monitor their sleep when they were presenting the programme and on their days off.
Both Sarah Montague and Evan Davis both naturally preferred late evenings over early mornings.
Prof Russell Foster announced the results on the programme, showing them both get up for work at 03:20 and at about 08:00 on a day off.
And then Sarah was told she was always in bed before midnight and often between 22:00 and 23:00.
Here's a contracted exchange of what followed:
Evan: "I'm going to bed much earlier than that."
Russell: "No, on two of those nights you were going to bed at two in the morning."
Evan: "No, no, no, no, no."
Russell: "You are chronically sleep deprived."
Evan: "We should say this was over the bank holiday weekend."
Sarah: "All right Evan, stop trying to excuse your behaviour."