By KATE SMITH

Last updated at 23:07 23 February 2008

You'd hardly know I was ill if you were to look at me. I go out with my friends, have a drink, travel, work, all the things everyone else does.

But at the back of my mind there is always a number - the average life expectancy for someone with my disease. That number is 31. I am 29.

I have cystic fibrosis. It's an incurable, genetic disease, where sufferers have thick mucus clogging their lungs.

Because of scarring from infection, a sufferer will either slowly suffocate - leaving their lungs unable to supply enough oxygen to the body - or their immune system loses the battle against infections.

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Two years to live: Brave Kate Smith

Should both parents have the gene, there is a one-in-four chance their child will have it. I do, but thankfully my younger brother Nick, and elder brother Alex, don't.

When I was diagnosed at five, the average life expectancy was 17, but each case is different. Improved medication and physiotherapy have changed my life.

Blowing out the candles on my 18th birthday cake felt very good indeed. Given my health problems- I've been admitted to hospital at least a dozen times with infections, sometimes for several months - I could have hidden away and given up.

Instead, I have lived life to the full - parties, travel and romance. I love new sports and I've been whitewater-rafting, tandem sky-diving and bungee-jumping in Australia. I know I've got a lot to pack in.

When I'm asked what is the worst part of my illness, I'd have to say the exhaustion. The rigorous exercise and physiotherapy regime required to help loosen the mucus on the lungs would tire anyone.

It includes swimming, yoga, gym and physiotherapy where the rib cage is beaten with cupped hands. The reduced lung capacity makes it harder still to cope with everyday life, let alone a full-time job.

The effect of absorbing a cocktail of drugs - up to 50 pills a day - plus inhalers, also saps the energy.

The onset of infection will often bring appalling pains in my chest and either side of my spine. Cystic fibrosis affects life in subtler ways, too. I never leave my hair wet, because the cold and damp would make my lungs produce more mucus.

I also avoid mould, especially in fruit, which contains the staphylococcus aureus bacteria that can grow in cystic fibrosis mucus.

Despite this, my mum Moya and dad Phil - a chemistry teacher and a BA pilot - never wrapped me in cotton wool.

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Support: Kate with brothers Alex, left, and Nick, who are not sufferers

There were no restrictions on me. My mother always threw me into exercise - swimming, dancing, trampolining and gymnastics - and I have continued into adulthood.

Some other parents didn't get it. I remember one mum telling me I was not to blow up balloons at a party: far too strenuous for a frail little thing like me, she said. Fine, I thought, I'll sit in the corner, chill out and eat the food.

Of course, my parents didn't burden me with all the details about the illness immediately but I knew I was different.

When I was 12, I used to tell each of my family before I went to bed that I loved them - just in case I died in my sleep. This was before I understood that sufferers rarely die without warning.

My personality has been shaped by the disease, too. I've never taken the small things in life seriously and I am not easily offended or jealous.

At school I was puzzled by my friends' obsessions with trivia. You're unhappy with your hair? Really? Oddly, I've become more girly in adulthood.

As I moved from school to further education and work, I found grooming and make-up a useful way to cope with the illness.

If I can still be bothered to do my hair and make-up, then I'm not that ill. I might feel awful, but I don't have to look awful as well.

There were a few times when I was too ill to go to school but I still got two A-levels and a degree in psychology at Kingston University, in South-West London. Students treated me no differently to anyone else, even if my housemates in Kingston could tell when I was in by my coughing.

In my early 20s I worked for the publisher Haymarket, but a severe infection brought on by my illness forced me to quit. Abandoning my career was the hardest decision I've made, but there was little choice.

I coughed constantly in the office and was so exhausted one day that I slept under my desk during my lunch break, asking my boss to wake me when he got back.

This might sound odd, but at 23 I retrained as an aerobics teacher. The effort of keeping fit and to a professional standard actually improved my health.

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High-rise thrills: Kate preparing to bungee jump

I was able to double my lung capacity - a crucial measure of my fitness - from 1.5 litres to three litres.

I liked the physical challenge, but decided to return to Kingston to do a postgraduate diploma in psychology, at the same time working two days a week in the prison service.

Because I wasn't earning enough to pay rent, I moved home with my parents in Sunbury-on-Thames, Surrey.

In a funny way, I know I have exceeded my parents' wildest hopes. When I was diagnosed, I was not expected to make it into my 20s. Every day since has been worthwhile and all the better for their support.

They haven't batted an eyelid at the extravagant things I've done. They even trusted me to go to Ibiza with girlfriends at 16. I just danced the week away. My parents' trust has made me strong.

My illness has always made me value relationships and be wary of fickle people. My early relationships were with boys from my crowd of friends, so I never had to explain that I had cystic fibrosis.

In my mid-20s, however, I was asked out on dates by men who didn't know me so well. That meant I had to choose the right moment to mention my illness and if it was an issue, I would walk away.

One man reacted in a bizarre way. He said he felt he'd been cursed, falling for someone who was ill. So cystic fibrosis has one advantage - it sifts out the nice guys from the idiots.

Can I see myself getting married one day? I would love to. I will try everything once but it's different with relationships.

I could marry only if it felt absolutely right - an extension of my happiness. I'm not ruling out children, either, although it would be a medical decision.

Carrying a child could reduce my lung capacity, maybe permanently. By having a baby, would I reduce my life expectancy and my ability to care for the child? Would it be fair on the child and its father?

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Water rush: Kate and friends white-water rafting

Cystic fibrosis is with me day and night but the right treatment may hold it at bay. Techniques have developed rapidly in the past two decades. Medication is more tailored to the individual; physiotherapy is more sophisticated and intensive.

In the morning I take two medications through a nebuliser, which produces a fine spray that I inhale. I then try to cough up any mucus that has built up overnight. I take pills three times a day, many of them antibiotics, starting at breakfast.

I use three inhalers, two to prevent tightness in the lungs and one to prevent sinusitis.

Additionally, I take Ibuprofen and paracetamol for any pain either side of my spine. When I get home from work or university I am exhausted and generally flake out.

Then it's more nebulisers before doing some physiotherapy, having dinner, doing some university work and going to bed.

One of the most sophisticated drugs I use is Pulmozyme. When inhaled, it breaks down the mucus before percussive physiotherapy - a once or twicedaily beating of the ribcage lasting between 30 minutes and an hour to clear the lungs to dislodge the phlegm.

It can be administered by the patient, a therapist, a trained friend or a parent. As I say, it is tiring.

In more serious bouts of illness, I take intravenous antibiotics through a permanent tube in my arm.

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Stuck on him: With boyfriend Dan, who she met while fundraising

Antibiotics are constantly swapped so the bugs in your body can't build up immunities.

I swim and do yoga for an hour as many days a week as my energy levels allow to loosen the mucus on my lungs. I also use a Power-Plate - a vibrating platform - to strengthen joints.

The right food is essential, too, to keep up my energy. Protein is important to fight infections.

Guilt and anger are always there. Guilt because you worry you are a burden and anger when you're not getting the treatment you need.

My experiences of the NHS have generally been good, but sometimes horrific. Fortunately, I now attend a good cystic fibrosis clinic at Frimley Park Hospital in Surrey for monthly sessions. Dr Ron Knight, my consultant, is a godsend.

The infection that forced me to abandon my publishing job happened during a summer heatwave. My lung capacity went down to 30 per cent, considered high risk.

I admitted myself to hospital and had to wait six hours for a bed. I was utterly exhausted, my energy drained from me. Then it hit me - this is what people experience when they are very old. When I go I will feel like this. And do you know what? I didn't give a damn - I would have been content to slip away gently.

But it was not my time. When I awoke with a drip in my arm, I could feel my strength returning. It was clear that I wasn't going to die.

My fighting spirit was back. I began to get bored in hospital and when you're well enough to be annoyed, you're clearly getting better. Stroppy people survive.

That day changed my life. Everyone wonders what it will be like when they die. I gained a sense of peace and lost my fear of death.

You learn to manage people's reactions. It's like being in the limelight. This is why I've been able to speak at charity events to raise money for cystic fibrosis research. The last one, the Liv charity dinner, was attended by Gordon and Sarah Brown, whose son Fraser has cystic fibrosis.

So there I was explaining my illness in front of the Prime Minister and suddenly I got the giggles. I couldn't stop myself. I said how surreal it was to give such intimate details to a star-studded audience.

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Looking forward: Kate is planning a huge fundraising party for her 31st birthday

I've also been raising money with my own website, named after my childhood nickname Kitten. I had stickers and stamps made up with the website address. My friends and I would stick them on people in bars to persuade them to donate.

One day I received an email via the website from a guy who said he'd woken up with a sticker on his ear, a stamp on his hand and an evil hangover.

Could I explain what had happened? Eventually we met up. We've been going out since last summer.

I've never had to explain my condition to Dan, a rugby coach for Harlequins RL. He knew from the start because we met through my fundraising.

"I am interested in you - not your illness," he says.

With smarter treatment, sufferers are living longer. Some have made it into their 50s, depending on the severity of their condition. But many die in childhood, so the average life expectancy can only tell us so much.

I'm having a big fundraising party on my 31st birthday, the day I overtake my life expectancy. I have no idea how long I will live.

Cystic fibrosis has taught me so much --including humility. I know that when I die, it will be peaceful. In the meantime, I'm as busy as ever, making the most of my time.

Proceeds from Kate's website (www.Ivebeenkittened.com) go to the Cystic Fibrosis Trust (www.cftrust.org.uk)

No longer a death sentence

Cystic fibrosis affects the lungs and immune and digestive systems, and is one of the most common incurable hereditary life-threatening diseases in the UK, with 8,000 sufferers.

Advances in treatment mean life expectancy has increased from under ten years in the Sixties, to 40 to 50 years for babies born this year, says Dr Jim Littlewood, chairman of the Cystic Fibrosis Trust.

WHAT CAUSES IT?

A mutation in a gene which produces a protein known as the cystic fibrosis transmembrane conductance regulator (CFTR), responsible for the salt and water salt and water balance in mucus.

Mucus is fluid secreted by the mucous membranes, including sweat glands, respiratory passages, pancreas, stomach and intestines.

WHAT ARE THE SYMPTOMS?

CF causes the body to produce copious thick mucus. In early stages, if treatment is not started, a persistent 'rattling' cough and frequent chest infections are common. Allergic reactions can worsen breathing problems.

The disease also causes the pancreas, responsible for providing digestive juices which help break down food, to produce thickened mucus.

These thick secretions cause irreversible damage to the pancreas, a difficulty in absorbing nutrients in the stomach and ultimately malnutrition. In older patients damage to the pancreas will lead to diabetes.

Many may experience heartburn and bowel problems. In some, thickened secretions can also lead to liver failure.

'The combination of these increasingly worsening symptoms is what leads to an early death for many CF sufferers,' explains Dr Littlewood.

HOW IS IT TREATED?

Because CF affects many organs, treatment is handled in centres staffed by specialist doctors and nurses.

Medication - inhaled and intravenous drugs - helps clear mucus and fight infection. Drugs in capsules contain digestive enzymes to aid food absorption. Physiotherapy helps clear the lungs of mucus.

"The real hope is treatment of the basic genetic defect that causes CF," says Dr Littlewood.

"Clinical trials for gene therapy - in which a normal copy of the CFTR gene is placed into affected cells - are beginning this year in the UK."