There are nearly 12,000 centenarians in Britain today, but with more people reaching 100 how do scientific theories about life expectancy compare with the experience of those who have received a telegram from the Queen?

At the age of 102 Nora Hardwick posed naked as Miss November for a charity calendar.

"They couldn't get enough ladies for the 12 months… It was very tastefully done. I had a pink tulle scarf to hide the bits and pieces."

Born in November 1905, Mrs Hardwick has devoted her whole life to her local community as postmistress of Ancaster village in Lincolnshire. A member of the parish council for 35 years, she has helped raise enough money to buy playing fields for the local children.

As far as she is concerned, her philanthropic lifestyle has proved life-preserving.

Research has suggested a decrease in mortality figures among those who put others before themselves. The theory is that giving back can provide a sense of purpose and self-worth and result in the "helper's high" - a "physical sensation" resulting from the endorphin release after an act of kindness or generosity.

Some argue that these feelings can reduce stress, promote wellbeing and strengthen the immune system.

Helper's high Name: Nora Hardwick

Nora Hardwick Age: 106

106 Top tip: Put others first, drink whisky

Now 106, Mrs Hardwick is still putting others first, while enjoying the odd glass of whisky.

But what does the science say about the effect of an alcoholic beverage on life expectancy?

Deaths from liver disease in England reached record levels according to NHS figures in March 2012. Yet a university study has claimed that drinking tiny amounts of alcohol could possibly increase life expectancy, with the caveat that this anti-ageing experiment was only conducted with worms and not human beings.

One centenarian who did enjoy a martini was comedian and cigar-smoking actor George Burns, who died at the age of 100. "It takes only one drink to get me drunk. The trouble is, I can't remember if it's the thirteenth or the fourteenth," he famously joked.

Scientific theories have always tended to concentrate on the physical changes that we can make to our lifestyle in an attempt to avoid age related diseases and prolong life expectancy such as taking regular exercise and eating a balanced, healthy diet, rich in vitamins and minerals. Some studies have argued that a low calorie diet can increase average life expectancy by as much as 25 years.

Media playback is unsupported on your device Media caption At the age of 100 Peggy Hovell is still driving in life's fast lane

With a quarter of all children born today expected to live beyond the age of 100 does science really have all the answers when it comes to the secret to reaching 100?

"The science is slightly baffled by this, we still don't really understand what makes a centenarian because all of them are unique," says Prof Tim Spector, an expert on ageing from Kings College London.

For some centenarians the key to successful ageing is not as tangible as, for instance, eating five portions of fruit and vegetables a day.

Find out more How to Live Beyond 100 is on Monday 9 July at 22:35 BST on BBC One, and forms part of a season of programmes about ageing.

Find out more about the other programmes in the season here Or catch up later on iPlayer

"My twin sister was a terrible pessimist, she died when she was not yet 70 because she never laughed, never. Laughing is beautiful though," says 108-year-old Alice Herz-Sommer.

"I'm an optimist, for me it's only the good things, never a bad thought," she says.

Born in 1903, Mrs Herz-Sommer has managed to retain a positive outlook despite a horrific start to life. The oldest living survivor of the Holocaust, she was imprisoned in Terezin (also known as Theresienstadt) concentration camp, near Prague, with her young son Raphael.

She survived the war by playing the piano in concerts within the camp. Her husband died in Germany at Belsen concentration camp.

One centenarian's tips Stay curious

Be an optimist

Cultivate friendships

Learn what you can do without

Do not take yourself too seriously: We are just a drop in the ocean From A Garden of Eden in Hell: The Life of Alice Herz-Sommer

"In my opinion musicians are privileged people. It brings you from the first tone to another world, not in the world with supermarkets, and not with money, in a world with peace and beauty," she says.

According to Spector, there may be some truth in Herz-Sommer's endorsement of inner calm and optimism. In a new book, Identically Different, Spector focuses on research into epigenetics, or how your environment and the decisions you make could have an impact on your genetic code. Even with identical twins, minor changes in upbringing or attitude could potentially alter the genetic path.

"What we are finding with our twin experiments is that one little factor difference can have a very major impact on them, and there is some evidence that mildly optimistic people do live longer than pessimistic people," says Spector.

Young at heart Name: Nina Jackson

Nina Jackson Age: 103

103 Top tip: Adapt to the times

He suggests that the difference in how a person views the same situation could actually have an impact on the genes affecting their brains which in turn could change certain chemicals and alter stress levels. All this could potentially have an effect on health and longevity.

A study published in the journal, Applied Psychology: Health and Wellbeing, in 2011 appears to back up this theory, claiming that positive thinkers and happier people do live longer.

Peggy Hovell, 100, is positive to the point of being fearless. Her plans for a charity parachute jump in her 90s were thwarted on medical advice.

"They said that if I did that jump it would probably tear my retina and give me blindness. I couldn't get a doctor's certificate after that," she says.

Rather than slowing down as she gets older, she is actually speeding up.

"I just love driving and I like driving fast," says the centenarian, who used to drive a van and deliver groceries during World War II.

The eternal optimist Name: Peggy Hovell

Peggy Hovell Age: 100

100 Top tip: Don't let age slow you down

This is not the behaviour you would come to expect of a woman of advancing years, but a driving assessment on her 96th birthday proved that Peggy Hovell's reactions were just as sharp as those of a driver 40 years younger.

Her willpower and sense of drive could be a a factor in her longevity, says Spector.

"If you have the will to do things then you have an optimistic view that you are not going to get hurt, you'll do something unexpected. If you are a bit of a pessimist and you say 'well if I do that I'm bound to break a leg and end up in hospital,' you just stay in bed all day."

For Spector, scientific research has shown that an active lifestyle is vital when it comes to living a long and healthy life. As well as your genetic make-up and environment, there is also an element of luck involved.

One thing centenarians do appear to have in common is their desire to keep living life. Nina Jackson, 103, defies age.

"I don't feel any different, sometimes I feel 50, sometimes younger still," says Mrs Jackson.

Her advice to all would-be centenarians - adapt to change and do not dwell on the past.

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