People who swim in sea waters are at higher risk of developing illnesses, a large-scale study carried out by The University of Exeter Medical School and Centre for Ecology and Hydrology has revealed.

The work was funded by the European Regional Development Fund and published in the International Journal of Epidemiology. According to the authors, it was the "first systematic review to evaluate evidence on the increased risk of acquiring illnesses from bathing in seawater compared with non-bathers".

The study compiles results from more than 120,000 people and includes data from high-income nations like the U.S., United Kingdom, Australia, New Zealand, Denmark, and Norway since 1961.

Compared to those who did not swim in sea waters, the chances of sea-swimmers developing an earache increased by 77% while the odds of a gastrointestinal illness increased by 29%. Twelve studies showed 44% higher odds of diarrhea while six studies suggested a 27% higher chance of stomach ache. The risks are also said to affect those who participate in bathing or sea sports such as surfing. 

"In high-income countries like the UK, there is a perception that there is little risk to health of spending time in the sea," explained Dr. Anne Leonard, a co-author from the University of Exeter Medical School.

"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 diarrhea. We think that this indicates that pollution is still an issue affecting swimmers in some of the world's richest countries."

Leonard believes that these illnesses are due to water pollution, affecting swimmers from even the richer nations. Seawater contamination is usually caused by industrial waste, sewage, and run-off from farmland. 

The authors mention that there were some limitations to the study, as they relied on self-report, varied in sample size and did not take other health conditions into consideration. Dr. Will Gaze, who was the supervisor of the study, assured that the researchers don’t want to "deter people from going into the sea, which has many health benefits such as improving physical fitness, wellbeing and connecting with nature".

He explained that while most would recover from the infections without any medical treatment, the study aimed to keep people informed about the potential risks, especially for vulnerable groups such as children, elders and those with pre-existing health conditions.

Studies have shown that human activities are the main factor behind marine pollution which has also affected plants and animals. Thousands of tons of waste (i.e. plastics, oil waste, radioactive waste, and sewage) continue to be dumped in the ocean on a daily basis.

"We have come a long way in terms of cleaning up our waters, but our evidence shows there is still work to be done. We hope this research will contribute to further efforts to clean up our coastal waters," Gaze added.