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Google probably already knows plenty about you – and the company looks set to learn a whole lot more. Last week, its health spin-off Verily launched Project Baseline, an ambitious attempt to collect reams of health data from 10,000 US-based volunteers.

By looking at people’s genes and microbiomes, and monitoring their sleep, physical activity and general well-being over four years, the team behind the project hopes to find clues that might predict the onset of diseases like cancer and heart disease.

“Baseline is an incredible opportunity to better understand the biological underpinnings of health and transition to disease,” says , a cardiologist at Stanford University in California, who is working on the project.

“I think it’s fascinating,” says , who leads deCODE Genetics, a company sequencing the genomes of people in Iceland. But Stefánsson says 10,000 people is too small a sample for the study. “Given the size and financial scope of Google, this is a small study,” he says.

Watch and learn

Every volunteer will undergo detailed medical tests once a year, offering up blood, saliva, sweat, urine and even their tears. They will also be given a Verily – a wearable device that tracks movement, heart rate and rhythm, and changes in the skin’s electrical conductance.

An additional bed sensor will measure the duration of sleep. Volunteers will also use an app, which will send them regular questionnaires on their health and well-being, as well as tests for cognition.

“The participants will receive modest reimbursements for their time,” says at Duke University in Durham, North Carolina, who is also involved in the project. “We will also release results back to them periodically.”

This is not the first large-scale population health study. The , for example, was launched in 1948, and has collected surveys on the diet and lifestyles of three generations of people living in Massachusetts – around 15,000 people so far. That study played a key role in helping us understand how smoking, cholesterol, exercise and other factors influence the risk of heart disease and stroke.

And huge genome studies are under way around the world. Nationwide programmes are sequencing the genomes of and vast swathes of the populations of countries including Iceland, Denmark and .

Data deluge

“This study is different,” says Hernandez. He says Project Baseline will collect more data than other studies. The company will continue to develop technologies that will be incorporated into the study as they emerge, he says.

“The molecular, sensory and software tools and technologies we are developing will seamlessly integrate, organise and activate multi-dimensional health data from lots of different sources, many of which have never been combined for a single individual,” says Verily’s chief medical officer .

at the University of Bath in the UK, who is not involved, agrees. “They’re also getting insights 24 hours a day,” he says.

Even so, studies that assess healthy people need to be huge to pick up differences that might be linked to health and disease, says Stefánsson. We share hundreds of common genetic variants, each of which have a tiny impact on our health, he says.

Size matters

“The studies of blood that have given us interesting insights have involved tens of thousands of people, not 10 thousand,” says Stefánsson, whose deCODE genetics study has so far drawn on data from around 400,000 people. “I’m a bit concerned that the study is not large enough.”

And Piwek questions the reliability of the data that will be collected as part of Project Baseline. “Different brands of devices can differ by 25 per cent in the number of steps they count,” he says.

So what will happen to this data? Verily is promising that all collected data will be anonymised, encrypted and securely stored. “Individuals administering the study will gain access to the data in a need-to-know basis, with permission audited periodically,” says Mega.

Ultimately, the company will offer de-identified data to researchers and organisations on a case-by-case basis.

At the moment, Verily plans to offer the data for free, says Hernandez. The team says data will not be sold to advertisers and insurance companies. “The data will only be made available to potential partners that believe and want to contribute to the Baseline mission to understand health and the transition to disease,” says Mega.

Read more: Too much information: Better health from big data