Gum disease linked to worsening dementia symptoms

"How brushing your teeth properly can ward of the symptoms of dementia," is the misleading headline in the Daily Mail.

In the study it reports on, all the participants already had dementia related to Alzheimer's disease. What the researchers wanted to do was investigate whether gum disease worsened the symptoms.

Sixty people with mild or moderate dementia were included in the study and followed for six months. Assessments of dementia severity and dental health were made at the beginning and end of the study.

Researchers found that the presence of gum disease at the beginning of the study was not related to participants' cognitive state at that point. However, it did appear to be associated to a six-fold increase in cognitive decline over a six-month follow-up period.

However, we can't say for certain whether the gum disease is causing the cognitive decline. All the participants had dementia at the start of the study, but only some had gum disease. This muddles the picture, as we are not able to determine a "direction of travel". It would have been more useful if all the participants had dementia, but did not have gum disease (or vice versa).

Factors other than gum disease may be contributing to the differences, and the small sample size means that any result could be due to chance.

Therefore, we don't know whether keeping better care of teeth might have a beneficial effect for those with dementia. That said, it certainly wouldn't hurt. 

Where did the story come from?

The study was carried out by researchers from a number of institutions, including Kings College London and the University of Southampton. 

Funding was provided by the Dunhill Medical Trust – a UK-based charitable company that makes research grants related to ageing and older people.

The study was published in the open-access, peer-reviewed medical journal PLOS ONE, which can be read for free online or downloaded as a PDF.

Competing interests were reported by two members of the study team, one of whom received research support from the Dunhill Medical Trust. The other had received research support from the Dunhill Medical Trust, the Oral and Dental Research Trust, Colgate Palmolive and GlaxoSmithKline.

Many of the UK's media's headlines – such as the Mail's "How brushing your teeth properly can ward of the symptoms of dementia" or The Daily Telegraph's "Brushing teeth regularly could ward off Alzheimer's disease" – are misleading. They give the impression that the study was looking at whether preventing gum disease would prevent Alzheimer's disease. In fact, everyone who took part in the study already had Alzheimer's.

Headlines aside, the actual results have largely been reported accurately in the media.

The Telegraph included a quote from Dr Doug Brown, Director of Research and Development at the Alzheimer's Society. He said: "This small study suggests that people who have both Alzheimer's and gum disease declined in memory and thinking more quickly than those who had better dental health. It's unclear however, whether this is cause or effect – if the gum disease is triggering the faster decline of dementia, or vice versa." This highlights an important limitation of the study.

What kind of research was this?

This was a cohort study which aimed to assess whether periodontitis (the medical term for gum disease) is associated with an increase in severity of dementia and cognitive decline in people with Alzheimer's disease.

As the study recruited people who already had Alzheimer's disease, it is unclear whether the gum disease might have contributed to causing the condition, as we cannot tell which condition occurred first. While the presence of gum disease might have affected the rate of cognitive decline after this point, it is also possible that other factors could be having an effect. For example, if those with gum disease also have poorer general health, this might have an impact.

However, this study does provide a possible link for further investigation.

What did the research involve?

The researchers included 60 non-smoking people with mild to moderate dementia who were not living in nursing homes. Participants were included if they had:

• at least 10 teeth
• not received treatment for gum disease in the previous six months
• capacity to consent for themselves to take part in the study

At the study's start, cognition (mental functioning, such as memory and language skills) was tested using two accepted tools: the Alzheimer's Disease Assessment Scale (ADAS-cog) as the main measure and the standardized Mini-Mental State Examination (sMMSE) as a secondary measure. Following these assessments, a blood sample was taken and tested for antibodies against bacteria related to gum disease.

The dental health of participants was assessed by a research dental hygienist. The measures of dental health assessed included:

• number of teeth
• measure of gum disease (including number of sites affected)
• plaque scores
• depth of any gaps between the gum and the root of the tooth (pockets)
• number of sites showing gum bleeding

Interviews with the participants' main caregivers were conducted to assess medical and dental history, including treatment for gum disease and medication use over the previous six months.

These assessments were carried out again at the end of the study, six months later.

Statistical analyses were performed to look at whether people with gum disease showed a different pattern of cognitive decline to those who did not have the condition. The analyses took into account the following confounding factors at the start of the study: 

• participants' age
• gender
• cognitive status

What were the basic results?

The participants were, on average, 77.7 years old and the group was evenly split between men and women. At the beginning of the study, 22 participants (37.3%) had gum disease. There was no relationship between how severe a person's cognitive impairment was and the presence of gum disease at the start of the study.

Six months later, at the final assessment, 52 participants were able to be assessed. Of the participants with gum disease at the start, 15 (75%) continued to have the condition and two new cases were found in participants that had previously not had it.

People who had gum disease at the start of the study were found to have, on average, about a six-point worsening of their ADAS-cog score after the six-month follow-up period, whereas those who did not have gum disease only had about a one-point worsening, on average. This association still remained after adjustment for participants' age, gender and cognitive score at the start of the study.

Gum disease initially showed a similar relationship to change in the secondary cognitive measure, the sMMSE, but this was no longer statistically significant after adjustment.

How did the researchers interpret the results?

The researchers conclude: "Our data showed that periodontitis is associated with an increase in cognitive decline in Alzheimer's Disease, independent to baseline cognitive state."

Conclusion

This cohort study aimed to assess whether the presence of gum disease is associated with an increase in severity of dementia and cognitive decline in people with Alzheimer's.

Researchers found the presence of gum disease at the beginning of the study was not related to cognitive state, but did appear to be associated with a six-fold greater cognitive decline over a six-month follow-up period.

The study has a number of limitations – for example, it was very small, so it is possible the findings are not representative of what would be seen in a larger sample. Most importantly, it is not able to prove cause and effect.

The participants already had dementia at the study's start, and some had gum disease, so we are not able to tell which occurred first and might be contributing to the other. While the presence of gum disease was linked to faster decline of one measure of cognitive ability (the ADAS-cog) it was not the case for a second measure (the sMMSE). Also, although some factors which might influence results were taken into account, such as age, other factors that could have had an impact were not. 

It is possible that people with gum disease also have poorer general health than those without the condition, or have other differences. Therefore, these differences could be having an impact on cognitive decline, rather than gum disease itself (called confounding). 

There have been a number of other studies that have assessed this link, and there is growing interest in whether dental health could have an impact on wider health.

These findings do add to the growing body of evidence, but more research is required to confirm the findings.

People with symptoms of dementia often neglect the basics of personal hygiene. If you are caring for a person with dementia, it is important that you encourage them to:

• wash their hands after using the toilet
• wash their "private parts" (including their anus) every day
• wash their face once a day
• take a shower or bath at least twice a week
• brush their teeth twice a day

Read more about personal hygiene for cared-for people.