Gum disease linked to increased risk of Alzheimer’s disease

"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.

A previous study 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 relationship between cause and effect.

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 that may 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.

Where did the story come from?

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 coverage 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 changes to teeth-brushing habits could reduce the risk of AD.

None of the news sources mentioned the possibility that some people with undiagnosed dementia might take less care of their teeth, leading to gum disease.

What kind of research was this?

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 check things.

The length of the study was also 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.

What did the research involve?

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. They chose to match two people without CP to every one person with it.

People were excluded from the study if:

• their age or sex was not clear from the data
• they already had a diagnosis of CP before 1997
• they already had AD before 1997, or before CP was diagnosed

The researchers analysed the data by looking at how CP was associated with AD after taking into account various other potential confounding risk factors associated with AD. They looked at whether there were differences between the two groups over time.

A further analysis looked only at people how had CP for at least 10 years before developing AD.

What were the basic results?

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.

People who had CP for at least 10 years had a higher risk of developing AD (hazard ratio 1.707, 95% confidence interval 1.152 to 2.528).

How did the researchers interpret the results?

The authors noted that the association between CP and AD was only detected in this study for 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 not being able to control the quality of the data available.

Conclusion

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:

• If the researchers had used more of the data available rather than taking a random sample to select a cohort, there may have been more cases of CP and AD to use in their analysis. This may have given a better insight into any association.
• The study did not give any details of how CP was treated or managed, so we don't know if there were any differences between people with CP who did and did not go on to develop AD.
• Although the researchers did take into consideration a number of other risk factors that could have affected the results (such as other health conditions), there may be others that affect the risk of developing both CP and AD that weren't taken into account.
• It's possible that the numbers of people with CP and those with AD may have been underestimated because of the way data were recorded in this database and how the conditions were diagnosed. For example, people may have had early AD, which caused them to have poor dental hygiene before a diagnosis of AD was made. Alternatively, CP may have been present in people in the non-CP group, as diagnosis is reliant on regular dental check-ups, which may not have taken place.

Further studies that look at larger numbers of people and follow them forwards in time would be needed to clarify any link between CP and AD.

These limitations aside, it's 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.