Children who live in areas their parents believe are unsafe are more likely to be overweight than those in safer neighbourhoods, scientists say.
If parents are worried, children are not allowed out
A University of Michigan team found children in the least "safe" places were four times as likely as those in the most safe to be overweight.
The study is in Archives of Pediatrics and Adolescent Medicine.
The researchers said more attention should be paid to the affect surroundings had on children's health.
In the US, almost 16% of six to 11-year-olds are overweight. In the UK, the number of six to 15-year-olds who are overweight has tripled since the early 1990s.
The researchers looked at data from 768 children and their families who had taken part in thee National Institute of Child Health and Human Development Study of Early Child Care and Youth Development, a study of families in 10 areas across America.
Parents completed questionnaires that assessed how safe they thought their areas were at the time their children were in first grade - when they were aged six.
The ratings were divided into quarters, with the first quartile perceived as the least safe and the fourth as safest.
Their children's height and weight had been measured in the laboratory when they were four-and-a half years old and again the spring of the first-grade year in school, when their average age was seven.
Body mass index (BMI) was calculated by dividing their weight in kilograms by the square of their height in meters.
It was found that 17% of children living in the first quartile were overweight, compared with 10% in the second quartile, 13% in the third quartile and only 4% of children living in the fourth, safest quartile.
This link was not affected by other factors such as the education levels or marital status of the children's mothers, racial or ethnic backgrounds or participation in after-school activities.
The researchers, led by Dr Julie Lumeng, wrote in the journal: "In effect, there may well be a relatively simple and straightforward relationship between living in a dangerous neighbourhood and overweight.
"Namely, in attempting to protect their children from harm, parents not only decrease the kind of physical activity that comes from playing outdoors in the neighbourhood but inadvertently increase the likelihood of sedentary activity that comes from staying indoors."
They add: "For the individual physician, these results suggest the need to understand the character of a child's neighbourhood when making recommendations for lifestyle and activity changes aimed at obesity prevention and treatment."
Dr David Haslam, clinical director of the UK's National Obesity Forum, said: "The researchers are making a valid point, but this is probably an element, rather than the whole explanation.
"These areas are likely to be the more deprived, which have less good food supplies and fewer places to play out."