A recently-published paper reveals that 10 per cent of New Zealanders in their 30s suffer from "chronic dry mouth" - a condition traditionally associated with older people.

Little is known about chronic dry mouth - known clinically as xerostomia - and researchers are only now beginning to get an idea of how many people it affects, the extent to which it affects their quality of life and its negative impact on oral health.

University of Otago School of Dentistry's Professor Murray Thomson is the world authority on the topic. He says just-published research produced by his group, as part of the 1000-person Dunedin Multidisciplinary Health and Development Study, found that 10 per cent of people in their early 30s are affected.

"Until now, it has been seen as a condition that affects older people - and that's the group that researchers had previously focused on," he says.

"What we have found is that xerostomia is experienced by a much younger age group and affects their oral health, as well as their day-to-day lives. They show higher rates of tooth decay, tooth loss and periodontal disease. They also report higher incidence of physical pain and functional limitations."

The research was published in the online journal Health and Quality of Life Outcomes earlier this month.

A related paper by Professor Thomson's team, published earlier this year in the Swedish journal Acta Odontologica Scandinavia found the prevalence of xerostomia was significantly higher among those taking antidepressants, iron supplements or narcotic analgesics such as codeine.

"In fact, those taking an antidepressant or iron supplement at age 32 had more than four times the odds of having xerostomia, while those taking narcotic analgesics had more than twice the odds," he says.

The prevalence was even greater among people who were taking two or more medications.

Professor Thomson says the association of dry mouth with anti-depressants and analgesics was largely predictable because their anticholinergic effects are well-known.

"However, the strong association with the taking of pharmacological-dose iron supplements was unexpected and more difficult to account for. Similar symptoms have been seen with iron deficiency, so it may be that the xerostomia is related to the condition more than the therapy," he says. "Whatever the cause, it is apparent from these studies that xerostomia is not a trivial condition for anyone, whether they are relatively healthy younger adults or older people.

"We need more intensive research to clarify the causes and natural history of the condition, and to find the best preventive and therapeutic approaches."