We're tired all the time, say 60 per cent of working mothers

A study has found that these women believe this is their "hardest decade", with many admitting to feeling stressed, missing sleep and skipping meals.

And their forties, when those who have delayed motherhood must cope with young children, are almost as bad.

According to the study, the pressure on these women is putting their health at risk.

About 85 per cent of those polled said they "frequently feel tired", and 59 percent of these "feel tired all the time".

Only 25 per cent regularly get seven or eight hours sleep a night, while 75 per cent were "lucky if they get six hours" - 40 per cent of these usually slept less than six hours a night.

Meanwhile, the vast majority in their 30s and 40s are stressed out and have to snack their way through the day because they don't have time to eat properly.

Seventy per cent of thirty-something women feel stressed on a weekly basis and 60 per cent cancelled social engagements because of the pressure.

Meanwhile, 78 per cent don't have time to eat properly, while 31 per cent admit to snacking all the time. Marina Crook, editor of Top Sante magazine, which carried out the research, said: "When thirtysomething women say they are 'tired and stressed out of their minds', they probably are.

"Tiredness and stress are the ailments of our age and combined with a poor diet they cause low immunity and illhealth.

"Sit-down family meals are no longer the norm, particularly during the working week. But women need to find time to relax and eat a healthy diet to be able to juggle the demands of work, motherhood and their busy, stressful lives.

"Our working lives are lasting longer than ever before. Our thirties and forties are so hectic, that by the time we reach our fifties, sixties and seventies - the time we should be more freed up to enjoy life - our health has already been seriously affected."

The health and wellbeing magazine's annual female health survey paints a picture of mothers who simply do not have enough hours in their day.

Fifteen per cent had left their jobs because of stress and 10 per cent even blamed it for ending relationships.

Meanwhile, 92 per cent said lack of sleep had weakened their body's defences. The study also revealed that poor diet and frantic lifestyles mean most women in their thirties and forties regularly get headaches, chest infections, heart palpitations or eczema.

Most of those surveyed knew that eating more fruit and vegetables, sleeping more and taking more exercise would make them feel better. But they couldn't do so because they had so little free time.

Miss Crook said: "Nearly all of these ailments are due to tiredness, stress and immunity. Thirty and fortysomething women have so many demands on their plate it's essential they find time to eat a more nutritionally balanced diet.

"Because they rely on snacks like sugary biscuits and salty crisps to get through the day, they feel even more tired and stressed."

So-called "supermums" such as Nicola Horlick, the City high-flyer who successfully combined five children with a job managing more than £5billion of pension fund investments, have been held up as paragons. But her marriage fell apart when her husband Tim admitted an affair in 2003 and left her.

In her first interview after the breakdown of her marriage, she admitted: "Maybe the answer is you can't necessarily have a happy marriage if you end up being a very high-powered woman." The financier has since remarried.

Denise Tyler, who runs the website mother@work, said the magazine's findings are unsurprising. Mrs Tyler, who has a daughter of six, said: "You feel as a mother and an employee you have to give 100 per cent to both, but it's often not possible. There's a lot of pressure to be supermum."

Latest figures reveal show the highest percentage rise in births has been seen among women in their late thirties.

There were 53.8 live births per 1,000 women aged 35-39 in 2006 - a seven per cent increase on the previous year, said the Office for National Statistics.