My first reaction on being asked to take part in the UK Biobank project was to be irritated that I fell into the right age bracket.
But there was no getting away from it: they wanted people aged 40-69, and lots of them.
The aim of the project, set up by the Department of Health, the Medical Research Council, the Scottish Government and the Wellcome Trust medical charity, is to collect medical and genetic data from 500,000 middle-aged people across the UK.
All this information will provide an unprecedented resource which should aid scientists in studying the prevention and treatment of serious diseases, from cancer and heart disease to debilitating joint problems.
This group has been chosen because they are the people who will get sick
Dr Tim Peakman Executive director
There is a catch. As the organisers put it in their letter of invitation: "Taking part is not intended to help you directly, but it should give future generations a much better chance of living their lives free of diseases that disable and kill".
So even if they picked up signs of a serious disease in my samples, I would remain none the wiser.
But I owe my life to treatment I have received from the NHS, twice over, so I decided to take part.
The Hounslow assessment centre - looking like a giant polling station full of colour-coded booths - was pretty empty when I arrived, but I was assured "business" had been good.
The organisers are working on the premise that around one in 10 people invited to take part will actually do so.
They have been pleased by the response. Since the project launched in 2007, some 330,000 people have signed up. In Bristol, the acceptance rate was 19%, and only Glasgow disappointed, with an acceptance rate of about 8%.
A robot stores away samples at -80C
The hope is that the magic 500,000 figure will be achieved midway through 2010.
Collecting data takes about two hours. First, there is a lifestyle questionnaire and a battery of mental tests.
It's a pretty detailed questionnaire, leaving very few stones unturned.
Did I really want to tell them how many sexual partners I had had?
Was a whole section probing my mood and motivation just a little bit too intrusive?
Still, they said the data was anonymised, so I took the plunge.
What really worried me was how bad I seemed to be at the memory tests.
Try memorising lists of numbers, and reproducing them in reverse order. I couldn't get past six digits.
Next up was a confidential trot through my medical history, and then a range of physical tests.
I can't say I was chuffed to find out that I have too much body fat, or that my right-hand grip force was so weak that my assessor looked a bit embarrassed.
It wasn't all bad news though - my bone mineral density was pretty good, and my waist circumference passed muster too.
THE BEAUTY OF URINE
Urine samples provide a potentially rich research resource for scientists
A sample provides a snapshot of the way the body's metabolism has been working over a period of several hours
Chemicals in the urine can show what food and drink we have consumed, and what medications we have taken - and how the body has dealt with them
Finally, I gave a blood and urine sample, to be packaged up along with my test results and sent for storage under a single barcode at the project's state-of-the-art processing centre on an unprepossessing industrial estate in Stockport.
There, a robot system modified from those used in the Japanese car industry, processes 21,000 samples from 650 people a day.
Speed is of the essence: to minimise the chance of samples beginning to degrade the project aims to transfer them from patient to storage within 30 hours.
Blow hard! Test of lung capacity
In total, 10 million vials of blood and urine will eventually be stored in the huge freezer facilities, cooled to -80C by liquid nitrogen.
The deep cold is essential to stop the blood samples separating out like curdled milk.
There the samples will stay, until required for scientific analysis.
Any medical treatment required by a person who has signed up to the project will be registered - anonymously - by the Biobank team, who can then pull out their samples - again registered under a unique catalogue number, and not a name - to try to determine why disease should have emerged.
Power of numbers
"Disease will appear in our cohort," said Dr Tim Peakman, the project's executive director.
Medical Research Council: £28m
Wellcome Trust: £28m
Department of Health: £5m
"This group has been chosen because they are the people who will get sick."
In fact, it was been calculated that the average 69-year-old has symptoms of three diseases.
Dr Peakman said the size of the study meant that disease was certain to emerge in numbers high enough to ensure analysis would get to the real causes - and not be blighted by specific circumstances that might apply only to individuals.
For instance, he predicts that 5,000 cases of type 2 diabetes will emerge three to four years into the project. Large numbers of other diseases, such as heart problems and cancer are sure to follow.
It truly is a chilling thought to realise that I had been asked to take part in the project because I am vulnerable to disease.
By way of thanks for my donation, I got a single sheet, giving a quick breakdown of a few of my results.
I have to say that it is frustrating to know that I will never get a full, detailed analysis.
But at least I can feel good that I might just have helped somebody else to beat disease several years down the line.
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