Researchers at the Harvard University in the US found that swilling with anti-bacterial fluid could be killing helpful microbes which live in the mouth and protect against obesity and diabetes.
They found that people who used mouthwash twice a day were around 55 per cent more likely to develop diabetes or dangerous blood sugar spikes, within three years.
"Most of these antibacterial ingredients in mouthwash are not selective," said Kaumudi Joshipura, professor at Harvard School of Public Health.
"In other words, they do not target specific oral bacteria - instead, these ingredients can act on a broad range of bacteria," Joshipura was quoted as saying by 'The Telegraph'.
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Over the study period around 17 per cent of people developed diabetes or pre-diabetes, but that rose to 20 per cent for those using mouthwash once a day, and 30 per cent for those who used it in the morning and evening.
According to Joshipura, helpful bacteria in the mouth can protect against diabetes and obesity, including microbes which help the body produce nitric oxide, which regulates insulin levels.
Nitric oxide is also important for regulating the metabolism, balancing energy and keeping blood sugar levels in check.