Forget the old adage early to bed, early to rise makes a man healthy, wealthy and wise. It is more likely to make him stressed.

Not only that, getting up early is also more likely to lead to muscle aches, cold symptoms, headaches and significantly worse moods.

Scientists have found that people who wake early have higher levels of the body's major stress hormone than those who like to sleep in.

A team from the University of Westminster asked 42 volunteers to take saliva samples eight times during the day for two days.

They took the first sample as soon as they woke up. Waking times ranged from 5.22 to 10.37am.

Analysis of the saliva from the half who woke earlier - before 7.21am - showed they had higher levels of cortisol, the body's main stress hormone, than those who woke later.

Their cortisol levels remained high all day.

Differences in the average number of hours asleep for the two groups could not account for this.

The researchers hope to discover whether high cortisol levels caused the early birds to wake early, or whether their hormone levels were high because of their early start.

Depression and suppressed immunity

Chronic stress is associated with depression and suppressed immunity.

In a 10-week follow-up study, the Westminster team found that early risers reported more muscle aches, cold symptoms and headaches - and significantly worse moods.

The researchers, led by Dr Angela Clow, issued a statement which said: "This work is interesting because it may provide a physiological basis for the often-reported difference between early and late risers.

"Early awakening was associated with greater powers of concentration, being busier and experiencing more hassles throughout the day as well as reporting more anger and less energy at the end of the day.

"On the other hand late wakers were more leisurely and less busy.

"It is possible that cortisol may contribute towards these differences in temperament as it is known to be able to influence mood and concentration."

Bursts of cortisol help prepare the body to deal with stressful situations by releasing stored energy and priming the muscles for action.

Cortisol also inhibits the body¿s sensitivity to pain by reducing inflammation.

The hormone is manufactured and released into the blood from the adrenal glands.

Once in the blood cortisol can pass freely throughout all tissues of the body, where it can exert diverse effects.

Professor Neil Douglas, director of the Scottish National Sleep Centre, warned that there were many factors that influenced cortisol levels in the body, including age and obesity.

He said in most people cortisol levels peaked at 8am and reached their low point at midnight.