Large–scale study reveals targets for obesity prevention, wisdom of walkable communities.
Using a larger dataset than for any previous human movement study, National Institutes of Health–funded researchers at Stanford University in Palo Alto, California, have tracked physical activity by population for more than 100 countries. Their research follows on a recent estimate that more than 5 million people die each year from causes associated with inactivity.

The large–scale study of daily step data from anonymous smartphone users dials in on how countries, genders, and community types fare in terms of physical activity and what results may mean for intervention efforts around physical activity and obesity.

The study was published July 10, 2017, in the advance online edition of the journal Nature.

The users whose data contributed to this study subscribed to the Azumio Argus app, a free application for tracking physical activity and other health behaviors.

In their study, Scott L. Delp, PhD, James H. Clark Professor of Bioengineering and director of the Mobilize Center at Stanford University, and colleagues analyzed 68 million days of minute–by–minute step recordings from 717,527 anonymous users of the smartphone app. Participation spanned 111 countries, but the researchers focused their study on 46 countries, each with at least 1,000 users. Of those, 90 percent of users were from 32 high income countries and 10 percent were from 14 middle income countries. The Stanford Mobilize Center is an NIH Big Data 2 Knowledge Center of Excellence.

“The study is 1,000 times larger than any previous study on human movement,” said Delp.

In addition to the step records, the researchers accessed age, gender, and height and weight status of users who registered the smartphone app. They used the same calculation that economists use for income inequality – called the Gini index – to calculate activity inequality by country.

Globally, the average user recorded about 5,000 steps per day. The smartphone data reflected the degree of difference, or inequality, for activity among people within a given country. By comparing countries with more uniform activity patterns and those with unequal activity, certain patterns and health dynamics emerged. For instance, countries with the greatest activity inequality are also the countries with the greatest obesity problem. Individuals in the five countries with the greatest activity inequality are nearly 200 percent more likely to be obese than individuals from the five countries with the lowest activity inequality.

The researchers report that countries with greater activity variation also have a larger proportion of inactive women. They found that in countries where activity is more uniform among members of the population, such as Japan, males and females are similarly active. But in countries with greater activity disparity, such as Saudi Arabia and the United States, there is disproportionately reduced activity for females. In fact, the gender gap accounts for 43 percent of activity inequality in those countries, according to the authors. They also found that the prevalence for obesity increases faster for females than males as population–wide activity decreases.

Data from 69 U.S. cities showed that higher walkability scores are associated with lower activity inequality. Higher walkability is associated with significantly more daily steps across all age, gender, and body–mass–index categories. However, the researchers found that women recorded comparatively less activity than men in places that are less walkable.