After new research shows sleeping badly could lead to memory problems later in life, and a separate survey suggests 70% of people feel they don't get enough shut-eye, experts discuss how sleep - or the lack of it - affects our health.
By Lisa Salmon Sleeping badly can make you feel wretched the next day - but new research suggests it may also have serious health implications later in life.
A US study has found that poor sleep may be linked to the creation of deposits in the brain that are a precursor to Alzheimer's disease, the most common form of dementia affecting 465,000 people in the UK.
And it seems there are plenty of Britons on the edge of that minefield. In a recent survey for Ikea, 70% of those questioned said they didn't feel they got enough sleep.
There are likely to be many reasons for the association between sleep and good health - for one thing, people who sleep badly tend to have compromised immune systems, says Professor Kevin Morgan, director of the Clinical Sleep Research Unit at Loughborough University.
Various studies have suggested a link between lack of sleep and increased blood pressure, inflammation, the risk of heart conditions, cancer and diabetes.
Indeed, a Harvard Medical School study last year found that men getting the least deep sleep were at 83% greater risk of having high blood pressure, which can lead to heart disease and stroke, than those getting the most sleep.
And Morgan cautiously confirms there "may be" a link between lack of sleep and such conditions, although insists more research is needed.
"Certainly, there's a long-term pay off for not sorting out disordered sleep," he warns. "There's an unexplained but robust relationship between how long we feel we sleep, and how long we live for."
Research shows that people who estimate they sleep for shorter or longer periods will die earlier than those who are in the middle of the spectrum and sleep for an average of just under seven hours a night, explains Morgan.
"There's a link between our sleep and our health - I'd be surprised if there wasn't," he adds.
The latest sleep study, from Washington University, examined people aged between 45 and 80 with no memory problems, half of whom had a family history of Alzheimer's.
It was found that around 25% of participants had preclinical Alzheimer's - that is, evidence of amyloid plaques, a type of protein deposit, in the brain.
Such plaques, which are thought to cause brain cell damage, form in Alzheimer's disease about 10 to 15 years before any symptoms appear.
People who slept badly, either waking up very frequently or spending a lot of their time in bed awake, had a higher chance of having plaques.
The study's author, Dr Yo-El Ju, a Washington University neurology professor, says: "It's possible that poor sleep quality over the years increases the chance of getting amyloid plaques, but it's also possible that having amyloid plaques leads to poor sleep quality."
She says it will take years of additional research to understand the relationship fully, but in the meantime stresses the importance of making an effort to sleep well.
"I think everyone, not just people who have family history of Alzheimer's disease, should prioritise their sleep," she urges.
"We all have so many obligations or habits that cut into our sleep, so we really have to make an active decision to make the time and effort to get good sleep."
Morgan agrees that focusing on good quality sleep is beneficial for health.
"People understand things about diet and exercise, but the third great pillar of our wellbeing is our sleep, and people know almost nothing about it," he says. "We still hold on to ideas that are utterly nonsensical."
One such idea, he says, is that we need eight hours sleep a night. "Nobody has any idea where this value came from - it has no basis in science and is probably a result of Victorian moral judgment."
He says the average amount of sleep per night is around seven hours, but how much sleep each person needs may differ widely.
"The answer to the question, 'How much sleep should I get?' is enough sleep for you to awake refreshed and face the following day efficient enough to do everything you feel you ought to," he says.
"If the amount you need to achieve that is three hours, fine. If it's seven or nine hours, fine. The answer is not a number."
How to sleep well Dr Yo-El Ju's tips for getting a better night's sleep: :: Go to bed and get up at the same time every day. The best sleep occurs when the body's clock is in sleep mode, and the best way to set this clock is to wake up and go to bed at consistent hours.
:: Avoid caffeine after mid-afternoon. Even if you fall asleep with caffeine in your system, it makes sleep light and restless.
:: Alcohol can make you sleepy initially, but causes many awakenings in the night, so moderate drinkers should give themselves one to two alcohol-free hours before going to bed.
:: Exercise during the day deepens sleep that night. However, exercising just before bedtime may wake the body up, so avoid hitting the gym late in the evening.
:: Watching TV, eating, surfing the internet, texting, or doing other activities in bed apart from sleeping, can teach the body bad habits about staying awake while under the covers.
:: If you have persistent sleep problems, seeing a sleep specialist can be very helpful. Many sleep problems, such as sleep apnoea, restless legs and insomnia, can be treated.