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"Gum disease sufferers 70% more likely to get dementia," The Times reports. A Taiwanese study found that people with a 10-year or longer history of chronic periodontitis (CP) had a small but significant increased risk of developing Alzheimer's disease (AD).
Gum disease is an umbrella term used to refer to a number of conditions that can affect the gums – ranging from gingivitis, which can cause bleeding gums, to CP, where extensive damage to the gums and underlying bones can lead to tooth loss. This study only looked at CP.
Previous research we discussed in 2016 did find a link between gum disease and worsening dementia symptoms. But because the people taking part in the study had already been diagnosed with dementia, the picture was muddled, as it was hard to determine a causal relationship.
This latest study found that people who had CP for at least 10 years had an estimated 70% higher risk of developing AD than people without CP.
However, although this increase was judged to be statistically significant (not the result of chance), it was still a very small increase. Only around 1 in 100 people with CP who took part in the study went on to develop AD. It was also not possible to tell whether the results were influenced by people having early undiagnosed AD, which could have led to poorer oral hygiene.
These limitations aside, the study gives another good reason to keep your teeth and gums healthy.
Read more about dental health.
The study was carried out by researchers from Chung Shan Medical University and the National Defense Medical Center, both in Taiwan, without a specific source of funding. It was published in the peer-reviewed medical journal Alzheimer's Research and Therapy.
Coverage of the story in the newspapers was mixed. The Times' and the Mail Online's reports didn't make it entirely clear that the risk of AD only applied to people who had CP for at least 10 years.
The Mail Online also implied that brushing your teeth more could reduce the risk of dementia. Although frequent and effective teeth brushing is associated with reducing the risk of gum disease, it wasn't clear from this study whether changing teeth-brushing habits could reduce the risk of AD.
None of the news sources mentioned the possibility that some people with undiagnosed dementia might not take as good care of their teeth, leading to gum disease.
This was a retrospective cohort study, where researchers looked at a national health database to find people who had CP and then checked whether they developed AD at a later date, comparing them with people who did not have CP.
This is an appropriate study design for looking at how different health conditions may be related to each other over time. However, using existing health records can be difficult if data are missing or unclear, as there is rarely an opportunity to go back and clarify things.
The length of the study was determined by how long the database had been running, rather than by how long it would have been useful to follow the people in the study for.
It's also not possible to tell if the gum disease started because of poor dental hygiene due to someone being in the early stages of undiagnosed AD, rather than the other way round.
The researchers used data from the National Health Insurance Program of Taiwan, which covers 99% of the country's residents. They analysed data recorded between 1996 and 2013. Rather than looking at everyone in the database, they took a random sample of 1 million people – around 4.5% of the whole database.
From this sample, they selected two groups of people aged 50 or older to compare. The first group was made up of 9,291 people who had a diagnosis of CP. The second group was made up of 18,672 people who were similar to the first group in terms of age, sex and number of years in the dataset, but who had not received a diagnosis of CP in the time period covered by the data. Two people without CP were matched to every one person with it.
People were excluded from the study if:
The researchers analysed the data by looking at how CP was associated with AD after taking into account various other potential confounding risk factors linked with AD. They looked at whether there were differences between the two groups over time.
A further analysis looked only at people who had CP for at least 10 years before developing AD.
By the end of the study, 115 people in the CP group (1.24%) and 208 people in the non-CP group (1.11%) had developed AD.
In the initial analysis, the researchers found no difference in the occurrence of AD between those who had CP and those who didn't during the first 10 years of observation. After around 10 years, some differences emerged between the groups.
The authors noted that the association between CP and AD was only detected in people who had CP for at least 10 years.
They acknowledged that being able to use a national medical database was beneficial for this kind of study, as it gave access to a wide population, but that it also had limitations, such as lack of control over the quality of the data available.
This was an interesting study that identified a possible link between two conditions, but it may not be a strong enough piece of research to provide definitive estimates of the size of the risk.
The study has a number of weaknesses:
Despite these limitations, it's still a good idea to take good care of your gums through regular brushing and flossing, and avoiding smoking.
Complications of gum disease can be unpleasant, including loss of teeth, and painful abscesses and ulcers.
Read more advice about keeping your mouth healthy.
Gum disease sufferers 70% more likely to get dementia. The Times, August 22 2017 (subscription required)
People with gum disease are 70 per cent more likely to get dementia, scientists say. The Sun, August 22 2017
Chen C, Wu Y, Chang Y. Association between chronic periodontitis and the risk of Alzheimer’s disease: a retrospective, population-based, matched-cohort study. Alzheimer's Research & Therapy. Published online August 8 2017
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