A study out of the University of Exeter has found that people who swim in the ocean have a higher risk of contracting ear ailments and gastrointestinal distress that non-sea bathers. The large-scale meta-study hypothesizes pollution is a major factor in increasing swimmers susceptibility to a variety of ailments.

The massive meta-analysis comprised 19 studies totaling over 120,000 people from a variety of high-income countries, including the US, UK, Australia and New Zealand. The striking results found that people who bathed in seawater had twice the chance of developing general ear ailments and a 29 percent higher chance of developing a gastrointestinal illness when compared to those who were not exposed to seawater.

"In high-income countries like the UK, there is a perception that there is little risk to health of spending time in the sea," explains one of the authors on the study, Anne Leonard. "However, our paper shows that spending time in the sea does increase the probability of developing illnesses, such as ear ailments and problems involving the digestive system, such as stomach ache and diarrhoea. We think that this indicates that pollution is still an issue affecting swimmers in some of the world's richest countries."

Despite the systematic nature of the analysis there are many limitations to the conclusions generated by this review. Definitions of seawater exposure varied among the studies included, so there is no specificity regarding frequency of exposure or distinctions between types of immersion. Only one study included in the review contained analysis of water samples so there is no data to specifically suggest these illnesses explicitly came from the seawater.

But this is not the first study of its kind from the University of Exeter. In January a team reported that regular surfers in coastal waters off the UK were three times more likely to have an antibiotic-resistant strain of E. coli bacteria in their guts than non-surfers. This study hypothesized that the surfers, who as a group are known to swallow larger volumes of seawater than regular swimmers, were regularly coming into contact with antibiotic-resistant bacteria from a variety of water run-off sources, including farm crops treated with manure and sewage.

Will Gaze, a supervisor on this latest study, suggests the intent of this research is not to deter people from swimming in the ocean, which is associated with many positive effects on physical fitness and well being, but to inform those more vulnerable to certain illnesses of the potential risks.

"Although most people will recover from infections with no medical treatment, they can prove more serious for vulnerable people, such as the very old or very young, or those with pre-existing health conditions," says Gaze. "We have come a long way in terms of cleaning up our waters, but our evidence shows there is still work to be done."

The study was published in the International Journal of Epidemiology.