Meera Senthilingam for CNN
Editor's note: Vital Signs is a monthly program bringing viewers health stories from around the world.
(CNN) -- Do you sleep between seven to nine hours per night? According to the experts this is the amount needed, on average, to keep our minds alert and our bodies healthy -- but many people aren't getting enough.
In the United States, for example, half the population sleeps less than seven hours during the week, according to the 2013 International Bedroom Poll. To make amends, many of us resort to catching up when circumstances allow -- whether it's sleeping in at the weekend or napping during the day.
But this catch-up can have its own impact on your body and when this catch-up becomes too much, it could even be a sign of an underlying health problem.
Sleeping in at weekends
The much-loved weekend snooze stems from the need to catch up on sleep lost during the week.
"That's an attempt to pay-back sleep deprivation," says Charles Czeisler, chief of the Division of Sleep and Circadian Disorders at the Brigham and Women's Hospital, in Boston.
But Czeisler is not an advocate of sleeping late at the weekend. He calls it "sleep binging," and says it's a break from consistency that leads to further disruption of our sleep cycles.
Sleep takes place in cycles of Rapid Eye Movement (REM) sleep and slow-wave sleep (Non-REM sleep) that alternate in approximately 90-minute cycles.
The extra hours of sleep, but more importantly the later time of awakening, at the weekend, lead to confusion and displacement in the body when people return to their weekday routine -- something Czeisler defines as "social jet lag."
"If you're getting up at 6 am and then noon, that's the equivalent of Boston to Paris [in time zones]," he says.
Making a habit of this is not a healthy lifestyle to lead, according to Czeisler. "It's a form of sleep bulimia with this chronic binging," he says. Such cycles disrupt sleep integrity, meaning people miss vital moments in their sleep cycle, such as REM cycles.
Even worse, in Czeisler's view, is the "crash and burn" cycle many live by where they skimp on sleep and drive themselves to the point of exhaustion, and then crash.
"[This] has adverse health consequences ... it's better to have consistency of sleep," he says.
The daytime nap can do wonders to improve alertness, performance and overall mood -- and for many, they offer a moment of relaxation.
Naps of 20-30 minutes -- and no longer -- are recommended by the U.S. National Sleep Foundation, to avoid grogginess and disruption of night sleep.
"It would be better not to get sleep deprived in the first place," says Czeisler. "However, once you are there, it is important to get as much sleep as possible as quickly as possible. That is where naps can help a lot."
But the desire to nap every day, despite having had a good night's sleep, could be a sign of something more serious -- particularly in countries where siestas are not the norm.
"Habitual daytime naps are more likely to be indicative of sleep deficiency, chronic ... disruption, or a disorder such as obstructive sleep apnea, depression or cancer," says Czeilser.
Professor Francesco Cappuccio and his team at the University of Warwick, in the UK, have explored what daily napping says about our health. The team studied the daytime napping habits of more than 16,000 men and women in the UK and found daily napping -- of both under and more than one hour -- to be a warning sign of an underlying health risk -- particularly respiratory problems.
"[Regular] napping is associated with increased risk of disease," says Cappuccio. As a result, keeping an eye on daily napping habits could help spot upcoming health conditions.
Mediterranean-style "siestas" were not included in the study as they were classed as a "pattern of life" associated with hot climates. "In Northern European countries it's usually a forced nap. You've been pushed to have a nap," says Cappuccio.
The reasons behind this increased risk still need to be explored.
"[This] does not prove that napping is dangerous," notes Czeisler. He instead says that if someone spends 8-9 hours per night in bed but is exhausted every afternoon, they should be evaluated for a sleep, or medical, disorder.
The week-long vacation snooze
When sleeping less than six hours per night, the missing hours accumulate over time. The reasons for such deprivation are wide-ranging, including jet lag, caring for children, working late and early rising -- but once paid back the need to sleep excessively should be gone. Cue the vacation sleep-fest.
"You can't pay it all back at once," says Czeisler, referring to the need to slowly pay back sleep loss accumulated over time.
According to Czeisler, one to two weeks is enough to pay back any accumulation of sleep loss in earlier days or weeks and after this it becomes physically hard to oversleep.
"Once you've paid back your deficiency, you can't really oversleep," says Czeisler. "You can be in bed for 14 hours but you're only really sleeping for eight hours."
If the desire to stay sleeping instead lasts for months on end, this could be a sign of fatigue rather than simple catch-up -- and a symptom of something more serious.
"If that [actual] sleep amount is 12 hours, then something is wrong," he says.
Sleeping late every day
"If you sleep a lot for no reason you should probably contact your doctor," says Cappuccio, who researches the benefits and impact of sleep on our health -- particularly the health of our hearts.
In another UK study, of 42 to 81-year-olds, he found that people who consistently slept more than eight hours per night, in the four years covered by the study, had a higher risk of stroke -- 46% higher. The cause of the increased risk remains to be shown but this extended sleep over prolonged periods of time could be useful as a marker for heart conditions later in life.
"I don't think there is too much sleep, [but] if you find yourself having difficulty getting up, there are reasons," says Cappuccio.
Cappuccio believes the risks associated with those prolonged hours asleep may extend beyond heart conditions to represent warning signs of depression, infection, inflammatory conditions and, in some, the early stages of cancer.
"That doesn't mean longer sleep causes these diseases," says Cappuccio. Instead, the fatigue keeping people in bed excessively is a symptom of something going wrong. "[It's] a consequence of disease, not the cause," he says.
Plenty of evidence to date has shown direct links between lack of sleep, or shift work, and a range of conditions including weight gain, diabetes, high blood pressure, stroke, and even the common cold. But little is known about the impact of excessive sleep -- rather than simply lazing in bed.
Further studies are needed to understand the biology behind the increased risks identified, but fatigue is a common symptom for many diseases and health conditions.
"When I was on college I got an infection ... at one point I was sleeping 20 hours a day," says Czeisler -- a Harvard graduate rowing crew member at the time of this infection. "My immune system was under attack, which does increase sleep duration," he says. In situations like this, sleep is needed to facilitate recovery.
Value your sleep
It's worth paying attention to the hours you spend sleeping, and in bed, as a means of monitoring and maintaining your health and wellbeing.
"Duration, timing and quality of sleep are the key factors," says Czeisler.
More studies are needed to truly understand the causes of the links seen between excessive sleep and various health conditions, but for the time being it may be wise to avoid those weekend binges and instead inject some routine into your dreams.
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