LONDON (Reuters) - The world's biggest and most detailed biomedical database opened its doors to researchers on Friday, offering scientists a unique glimpse into the health and lifestyles of 500,000 middle-aged Britons.

The UK Biobank - with more than 1,000 pieces of information about each participant plus samples of blood, urine and saliva - will be available to researchers worldwide, on the condition they put their findings back into the public domain.

The organisers said they had already received expressions of interest from both drug companies and academics, including the National Institutes of Health in the United States, which has no such equivalent biobank.

"We have managed to combine data breadth and data depth, and that is what makes it a unique resource for researchers around the world," the project's principal investigator, Rory Collins, told a news conference.

China, Sweden and other countries have also set up biobanks but the British one, which cost close to 100 million pounds ($160 million) to plan and develop, is the most comprehensive to date.

Volunteers first checked into the UK Biobank - which is backed by the government-backed Medical Research Council and the Wellcome Trust charity - between 2006 and 2010. It is only now, however, that the project is ready to open its doors to outside researchers.

The mapping of the human genome in 2000 allowed detailed analysis of genes, but experts are still grappling to understand how they interact with lifestyle and environment to determine why some people become sick and others do not.

Many common diseases are caused by multiple inherited and other factors - a mix of nature and nurture.

By questioning participants about everything from diet and exercise to sexual history, and allowing researchers to cross-reference this against medical records and genetic profiles, the UK Biobank offers a deep dive into myriad such factors.

GETTING SICK QUICK

Collins and his team chose to study people aged between 40 to 69 because this group will not keep researchers waiting too long before developing interesting conditions such as cancer, arthritis, diabetes, heart disease and dementia.

Their future health will be tracked through the state-run National Health Service, hopefully shedding light on why some people develop a particular disease and others do not.

Insights gained from this data-mining exercise - in which all the information is anonymised to protect participants' identity - could pave the way for the development of new medicines and disease prevention strategies.

Collins believes involving outside researchers will deepen the value of the collection as teams conduct extra analyses, such as sequencing the genes of biological samples. All the new information will be added to the database.

The UK Biobank has 15 million biological samples - 30 for each participant - stored in a giant freezer facility in northern England.

There are also plans to conduct whole-body scans for many participants, adding further information to a database that already includes the world's largest collection of eye images.

For people taking part in the UK Biobank, however, there is no financial or other gain in exchange for the two or three hours of testing they underwent to join the project.

The hope is simply that it will help their children, grandchildren and wider society.

"It is an amazing example of altruism of ordinary people," said Mike Rawlins, chairman of the UK Biobank board.

($1 = 0.6309 British pounds)

(Editing by Mark Potter)