Regular use of laxatives, a common treatment for constipation, may be associated with an increased risk of developing dementia than those who do not use them, according to a study.

The research, published in the journal Neurology, also found that people who used only osmotic laxatives, a type of laxative that attracts water to the colon to soften stool, had an even greater risk.

Other types of laxatives are bulk-forming, stool-softening, and stimulating, the resaerchers said. However, they noted that the study does not prove that laxatives cause dementia. It only shows an association.

"Constipation and laxative use are common among middle-aged and older adults," said study author Feng Sha, from the Chinese Academy of Sciences in Guangdong, China.

"However, regular laxative use may change the microbiome of the gut, possibly affecting nerve signalling from the gut to the brain or increasing the production of intestinal toxins that may affect the brain," Sha said.

The study found regular use of over-the-counter laxatives was associated with a higher risk of dementia, particularly in people who used multiple laxative types or osmotic laxatives.

Sha noted that osmotic and stimulant laxatives are not recommended for regular use, yet some people use them regularly.

The study involved 502,229 people in the UK biobank database with an average age of 57 who did not have dementia at the start of the study.

Of this group, 18,235 people, or 3.6 per cent, reported regularly using over-the-counter laxatives. Regular use was defined as using a laxative most days of the week during the month before the study.

Over an average of 10 years, 218 of those who regularly used laxatives, or 1.3 per cent, developed dementia. Of those who did not regularly use laxatives, 1,969 people, or 0.4 per cent, developed dementia.

After adjusting for factors such as age, sex, education, other illnesses and medication use, and a family history of dementia, researchers found people who regularly used laxatives had a 51 per cent increased risk of overall dementia compared to people who did not regularly use laxatives.

The risk of dementia also increased with the number of laxative types used. For people using one type of laxative, there was a 28 per cent increased risk, compared to a 90 per cent increased risk for people taking two or more types of laxatives.

However, among people using only one type, only those taking osmotic laxatives had a heightened risk, with a 64 per cent increase compared to those who did not use laxatives.

"Finding ways to reduce a person's risk of dementia by identifying risk factors that can be modified is crucial," said Sha.

"More research is needed to further investigate the link our research found between laxatives and dementia. If our findings are confirmed, medical professionals could encourage people to treat constipation by making lifestyle changes such as drinking more water, increasing dietary fibre and adding more activity into their daily lives," he added.

A limitation of the study is that dosage information for laxatives was not available so researchers could not explore the relationship between various laxative dosages and dementia.