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【Nature】饮食组学
http://www.nature.com/news/2011/110216/full/470320a.html
If a camera snaps everything you eat, you can't lie about it later. That's why scientists are building high-tech gadgets to measure the human 'exposome'.
Brendan Borrell
A decade ago, as part of a study on diet, psychologist Tom Baranowski was asked to recall everything he had eaten the previous day. A chicken dinner, he said confidently, remembering that he had prepared it for himself and his wife Janice. The thing was, he hadn't made chicken that night. It was only later that he realized he'd treated himself to a hamburger.
If Baranowski, who studies children's diets at Baylor College of Medicine in Houston, Texas, was an unlikely candidate for making such a mistake, consider how abysmal the dietary memories of everyone else must be. By observing his study subjects one day and following up the next, Baranowski has found that children routinely forget about 15% of the foods they have eaten, and more than 30% of the foods they do recall turn out to be figments of their imagination. Adults show similar patterns. "The errors of dietary assessment are overwhelming," says Baranowski.
These mistakes are more than a reminder of the human memory's fallibility: they threaten to undermine the foundations of modern medical epidemiology. In this field, researchers make associations between past events and experiences, and later ones such as the emergence of cancer or other diseases. But if the initial records are inaccurate, these associations can be weak, misleading or plain wrong. Although the problem is most jarring in studies of diet, it also infects investigations of exercise, stress, pollution or smoking — basically, anything that relies on people reporting their own exposures through interviews or questionnaires. "This is the weak part of epidemiology," says Paolo Vineis, an environmental epidemiologist at Imperial College London.
Baranowski and Vineis are at the forefront of a movement among health researchers to develop measurements of environmental exposures that are more precise and objective than questionnaires. Some are working to develop personalized exposure profiles using blood-based tests. Others want their study subjects to trot around town with sensors dangling off their bodies capturing their movements, snapping photos of their lunch and taking samples of the air they breathe. "We are getting to the point where you can conceive of doing a study with 500,000 people and giving them a cell-phone-sized device that they put in a charger every night," says David Balshaw, the exposure-biology programme manager at the National Institute for Environmental Health Sciences in Research Triangle Park, North Carolina.
Some researchers foresee a day when they will keep track of the entire spectrum of environmental exposures for a single individual, dubbed the 'exposome' (附录一). That's a long way off. In the meantime, Nature takes a look at efforts to measure three key elements of the exposome: air pollutants, physical activity and diet. Each of these is bringing the exposome one step closer to reality — and the questionnaire, with all its flaws, a step closer to extinction.
Breath by breath
The contraption fitted snugly inside a child's backpack. The tangle of green plastic tubes, filters, pumps, circuit boards and a hefty battery weighed about 3 kilograms and made a low hum when it was switched on and began sucking in air. Tiny filters were designed to collect continuous records of all the grit and grime a child in the Bronx would be exposed to during their pilgrimage from their apartment, through the New York City subway system to school and back again.
For geochemist Steven Chillrud, whose team built the device in 2004, it represented the future of exposure biology. In the United States, environmental scientists have traditionally estimated human exposure to airborne pollutants by analysing data from building-mounted sensors. But the shortcomings of this approach became clear in a landmark study1 published in 2005, in which researchers showed that levels of many hazardous compounds were higher inside homes than out. The findings made sense to Chillrud, who had already been thinking about the exposures of people living in New York City. "People do not live on buildings," he says.
To the New York City Police Department (NYPD), though, Chillrud's contraption was a potential terrorist threat. After four terrorists detonated bombs on London's public transport system on 7 July 2005, the NYPD had been conducting random searches on the subway system. When Chillrud stopped by the local police precinct to alert them to his planned study, officers were aghast, and even Chillrud admits his device looked intimidating. "We put a lot of effort into it," Chillrud says now, as he hoists it onto his desk at Columbia University's Lamont–Doherty Earth Observatory in Palisades, New York. "Then, the police shut us down." But they also offered the team a way forwards. "If we could shrink it to the size of a Walkman, we'd be back in business."
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作者:admin@医学,生命科学 2011-02-17 11:18
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