Stanford researchers find intriguing clues about obesity by counting steps via smartphones

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Indonesians meanwhile took the least steps of just 3,513 in a day. Step counts were highest in Hong Kong, where people took an average of 6,880 steps a day, followed by China, with 6,189 steps, and Ukraine, with 6,107 steps. What surprised researchers, however, was how greatly this gender step gap varied from country to country with negative consequences for women. However, the researchers found that women recorded comparatively less activity than men in places that are less walkable.

The data was compiled from a smartphone app, Azumio Argus, which tracks physical activity through mobile sensors.

The researchers have also concluded that such lack of inequality and such vast differences in "activity inequality" could be a major reason behind diseases like obesity that have gripped America.

Using data collected from smartphones, researchers from Stanford University analysed how many steps more than 700,000 people from around the world took each day in a bid to try and find out which factors determine obesity levels.

Put simply, this means that countries where everyone reported similar levels of activity had much lower obesity rates than countries which have a polarised mix of very active and very sedentary users.

But in countries with high inequality, like the USA and Saudi Arabia, it was women spending less time being active.

What did matter was something called "activity inequality" - essentially, the disparity between the most active people in a country and its most inactive. In other countries, though, where there were bigger gaps between those who walked a lot and those who walked only a little, obesity was significantly more of a problem.

The findings leaned most heavily on data from the 46 countries for which Azumio provided at least a thousand anonymized users, enough to form the basis for statistically valid inferences. And, because the phones collected data only when they were on the subjects' person, the research may have failed to capture time spent in other fitness activities where it is impractical to carry a phone, such as swimming. In countries with low obesity and low inequality like Japan, men and women had similar physical activity levels.

Health experts suggest regular physical activity as the best way to stay healthy.

One of the most interesting findings from the study was that the average number of steps taken in each country had little impact on predicting their obesity rates.

The researchers are sharing their findings on an activity inequality website, hoping their work will help improve public health campaigns against obesity and support policies to make cities more "walkable".

The researchers say using anonymous data from smartphones is an "immensely powerful tool" for conducting this kind of research.

Scott Delp, a professor of bioengineering and one of the researchers, said: "The study is 1,000 times larger than any previous study on human movement".

"This opens the door to new ways of doing science at a much larger scale", Delp said.

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