Digging in the sand can increase the risk of developing gastrointestinal diseases and diarrhea, U.S. research shows. (Samantha Critchell/The Associated Press)

Intestinal threats lurk beneath the sand at some beaches, and the closer the contact, the greater the chance of a fun day leading to a bout of diarrhea, a U.S. study shows.

People who dig in the sand are more likely to develop a gastrointestinal disease or get diarrhea than people who simply walk or swim at the beach, the study of 27,000 beach visitors said.

And people who bury their bodies are at even greater risk, the study recently published in the online edition of the American Journal of Epidemiology reported.

Children, who are more likely to play in sand and may get it in their mouths, stand the greatest chance of becoming ill, researchers from the University of North Carolina at Chapel Hill and the U.S. Environmental Protection Agency (EPA) concluded. Diarrhea and gastrointestinal problems were more common in about 13 per cent of people who dug in sand, and in about 23 per cent of those who were buried, they said.

Still, the overall rate of illness was under 10 per cent in any age group.

It's long been known that water contaminated with fecal material raises the chance of intestinal distress, but "this is one of the first studies to show an association between specific sand contact activities and illnesses," said Chris Heaney, a postdoctoral student at the university and lead author of the study.

The study was based on interviews with more than 27,000 people who visited seven freshwater and marine beaches between 2003 and 2005 and in 2007. All the beaches were within 11 kilometres of a sewage-treatment plant, but the water quality was within acceptable limits.

They were asked about their contact with sand the day they went to the beach, and then phoned 10 to 12 days later and asked about any health problems that had arisen since that day.

The results do not mean people should avoid the beach, but they should use a hand sanitizer or wash their hands after playing in sand, said Tim Wade, an EPA epidemiologist and the study's senior author.

The study is part of the EPA's National Epidemiological and Environmental Assessment of Recreational Water.