People who are "perfectly happy" get precisely seven hours and six minutes of shut eye, a new survey reveals.

We already knew that there's a strong link between the amount of sleep we get and our well-being - now it appears there is a very tight margin.

Participants who rated themselves "mostly happy" people sleep a little bit less than the "perfectly happy" people, getting seven hours.

And those who said they were "somewhat happy" snoozed for six hours 54 minutes, the study of 2,000 people shows.

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"Less than 6 hours 48 minutes hours of sleep meant complete unhappiness in relationships, constant worry, and never a shred of gratitude," the report states.

Seven hours is the minimum amount of sleep for adults recommended by the NHS - but perhaps hitting the snooze button for an extra six minutes is a good thing.

In line with previous research, the new study found women struggled the most to get a decent night's sleep, and those reporting the fewest hours also said they were the least happy.

But age is a big factors - the survey by mattress company Amerisleep also found that those 25 or younger get a lot of sleep regardless of happiness level.

Single people report sleeping the most, while separated people sleep the least.

Respondents who got the best sleep were more likely to meditate or take a shower before bedtime.

Activities associated with less sleep include working or playing video games, according to the report.

One in three of us suffers from poor sleep, with stress, computers and mobile devices, shift work patterns taking work home often blamed.

And the price of sleepless nights is more than just fatigue. As well as depression, lack of regular sleep is linked to raised risk of obesity, heart attack, stroke and diabetes - and it shortens your life expectancy.

However, while a lot of research tends to focus on the amount of time we sleep, scientists at Brigham and Women's Hospital have found routine is just as important.

They discovered people who go to bed at the same time every night are far more healthy and successful than their more spontaneous peers.

Using sleep diaries, the team measured sleep and circadian rhythms in 61 undergraduates at Harvard College for 30 days, then compared that data to their academic performance.

Overwhelmingly, students with irregular patterns of sleep and wakefulness had a lower grade point average than the rest.

They also hit snooze more often, rather than bounding out of bed, and struggled to get sleepy, due to irregular releases of melatonin - the hormone that makes us want to sleep.

Another recent study also suggests our routine - rather than the amount of time we sleep - is key.

It claims going to bed and waking up later on the weekends can raise your chances of getting heart disease.

Scientists from the University of Arizona in Tucson have even quantified the risk - they say each hour of going to bed later than normal is associated with an 11 percent increase.

This is the effect of what experts call "social jet lag", that is having different sleep patterns on the weekends than during the work week.

Sleeping in longer was found to have no health benefit if you have gone to bed at a later time than usual.

"These results indicate that sleep regularity, beyond sleep duration alone, plays a significant role in our health," said lead author Sierra B. Forbush, a research assistant at the university's Sleep and Health Research Program.

"This suggests that a regular sleep schedule may be an effective, relatively simple, and inexpensive preventative treatment for heart disease as well as many other health problems."

Insomnia is in the genes

Insomnia is often attributed to stress and anxiety but its cause could be genetic, according to recent research.

For the first time, an international team of researchers has found seven risk genes for the sleep disorder.

The breakthrough could lead to new treatments for the condition, which blights the lives of one in ten Britons.

A host of celebrities - including Madonna, George Clooney, Lady Gaga and Kim Cattrall - have all spoken about their difficulties in nodding off at night - and now scientists could help explain why.

The findings also suggested there are different genetic variants for men and women - with the latter being more susceptible.

Sleep specialist Professor Eus Van Someren, of Vrije University, Amsterdam and his colleagues mapped the DNA of more than 113,000 people from Britain and the Netherlands.