26/05/2016 06:18 BST | Updated 26/05/2017 06:12 BST

My Recipe for a Long Life

You have no death genes. You aren't programmed to die. We age by default. We're killed softly and slowly by the erosion of our genetic blueprint which suffers thousands of assaults daily from internal and external forces. Your longevity, however, is only 25% determined by your genes. The other 75% you're entirely in control of. You can manipulate the environment in which your genes operate i.e. your body, by the way you live.

You can encourage all your good genes to express themselves with a simple tool, unique to you, your lifestyle. You have within you the resources to increase your lifespan by prolonging your healthspan. Physical and mental health should be the lynchpins of your strategy and we can learn much from one of the longest living race on the planet, the Okinawans, off the coast of Japan.

To emulate their lifestyle - well, up to a point - follow these rules: no smoking or drinking, eat little meat, very little fat and sugar, practice hachi bu (stopping eating at the first sign of fullness), stay on your feet, meditate, keep up strong family and community support and remain optimistic. Do all this and you'll be rewarded by a long life, genes allowing. The Okinawans live to an average above 100!

I've been convinced for years exercise is key to a long, healthy life. It's like a multivitamin. It affects every single organ and system in your body for the better. It's literally the elixir of life - and of youth.

Ever since I read the research on the killer effects of sitting down I stand to do all my writing. I also believe in intermittent intensive exercise and I do it three times a week. I've adapted it to my personal regime which has 30 second hill climbs standing up on my spinning bike, then 30 seconds sitting down but pedalling fast. I do six of these with a two minute warm up and warm down. The whole programme takes 10 minutes and only three minutes of that is intense. There's loads of research to show it works and it keeps the weight off.

To push myself, and we need to as we get older just to maintain, I do the same programme in a hypoxic chamber where oxygen levels are so low it's like doing hill climbs on the top of Mont Blanc. Plus I try to walk three miles a day to meetings, to friends, to theatre, opera and museums.

Our bodies really hate being inactive. For thousands of years of our evolution we were running much of the time - active hunter-gatherers. Every member of the human race undertook exercise almost constantly every day of their lives while they were awake. The body hasn't so far evolved to cope with inactivity. It hasn't had time. It knows of no way to deal with the sedentary life. All it can do is decay.

Years ago I realised the only exercise I could do long-term was walking so I jettisoned my heels (and I used to wear dizzyingly high heels) and took to funky trainers in many colours to match my outfits. It meant I could walk anywhere anytime and walking became part of my life.

Recently I saw the film Youth and the two leading characters, played by Michael Caine and Harvey Keitel, were trying to put their old age to rights with long rambling conversations. But they weren't tucked up in easy chairs. They were walking. Walking. Walking. In the Swiss Alps. Not all of us can enjoy such luxury but we can walk. Walking and talking with a friend is an ideal way to keep everything ticking over and very good for mental health too. There's loads of research showing walking (briskly for half an hour each day) is the key to a long, healthy life and much better than arduous gym sessions.

There's a marvellous moment in the film Youth where a doctor declares the ageing Michael Caine character has a clean bill of health. "What shall I do now?" The doctor replies with, "Enjoy your youth." And in one fell swoop Michael Caine goes from pessimism to optimism, the essence of a young and hopeful outlook!

If I were to choose one factor above all the others to assure a long, happy life it would be optimism. Optimism can give you real resilience as you get older - it's a great healer. Research has shown that people with optimistic attitudes have fewer illnesses and recover more quickly from illness.

Optimists are more likely to feel that they can take charge of their health and not just passively slide into old age. They tend to take better care of themselves too. They sleep better, don't drink or smoke too much, exercise regularly and are freer from depression. They live longer and age more gently. It's worth cultivating optimism, believe me.

We must take responsibility to do what we can to enhance the quality of our extra years so that we can enjoy them as much as possible.

'YOUTH' is available on Digital Download now and will be out on DVD and Blu-ray from Monday 30th May