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Frequent teeth brushing may be linked with lower risk of diabetes

The Mail Online reports that brushing your teeth 3 times a day could ward off diabetes.

The report is prompted by a South Korean study that collected data from a health insurance system on the dental health and frequency of check-ups for over 180,000 people. It then linked this with records of raised blood sugar or prescriptions for diabetes drugs over an average 10-year follow-up.

The study found that having gum disease or a greater number of missing teeth was linked with increased chance of developing diabetes. Meanwhile increased teeth brushing – here defined as 3 or more times per day – was linked with 8% decreased risk of diabetes. (The study did not specify type of diabetes, but we can presume this is type 2 as the rarer type 1 is very unlikely to develop in older adults).

These findings do not prove that increased tooth brushing and tooth decay are themselves directly linked with diabetes. What is more likely is that other health and lifestyle factors associated with dental health are also associated with risk of diabetes. For example, people who consume more sugar may be more likely to have dental problems and diabetes. Similarly people more concerned for their dental health may be more likely to follow other positive health and lifestyle behaviours.

This is also a specific Korean population who may not be representative of the UK.

Following a healthy diet low in sugar and saturated fat, taking regular physical activity and maintaining a healthy weight are far more beneficial in reducing risk of type 2 diabetes.

However, good dental health is also important as it can help prevent gum disease.


Where did the story come from?

The study was carried out by researchers from the Ewha Womans University College of Medicine, Catholic University of Korea and Asian Medical Center, all in Seoul, South Korea. Funding was provided by the National Research Foundation of Korea and the Ministry of Education. The study was published in the journal Diabetologia and is freely available to access online.

The Mail coverage is slightly exaggerated in reporting a 14% decreased risk, which was from one small subgroup analysis in this study. The main finding was a less dramatic 8% decreased risk.


What kind of research was this?

This was a cohort study using data collected for a sample of the South Korean population in a National Health Insurance System (NHIS) database.

This study design can look at links between earlier exposures (such as dental health) and later outcomes (such as diabetes) but cannot prove cause and effect, because it is difficult to remove the influence of all the various health and lifestyle factors that may be involved in the links.


What did the research involve?

Almost all of the South Korean population are covered by the NHIS, which requires them to have a medical examination every 2 years. In 2015 researchers formed an NHIS Health Screening Cohort database (NHIS-HEALS), to gather information collected for a random sample of 541,866 people.

The 2-yearly medical examinations included health and lifestyle questionnaires, height and weight, and laboratory tests. Oral health was assessed by questionnaires on dental symptoms, frequency of dental checks and oral hygiene. Diagnosis of gum disease was also recorded in the database.

The researchers looked at data collected for people between 2003 and 2006 who did not have a diagnosis of diabetes. The definition of diabetes used in the study was having at least one fasting glucose sample of greater than 7mmol/l or prescription for diabetes drugs. After excluding those without information on dental health and with a previous diagnosis of diabetes they had a sample of 188,013 people.

They looked at follow-up to 2015 for these people (average 10 years) to see if anyone later developed diabetes according to this definition.

The researchers looked at the link with dental health taking account of variables including:

  • body mass index (BMI)
  • socioeconomic status
  • smoking and alcohol
  • physical activity (defined as performing at least 20 minutes of strenuous exercise once a week)
  • high blood pressure or cholesterol
  • kidney disease
  • cancer

What were the basic results?

The average age of people in the database was 53 years and 58% were men. Gum disease was recorded for 17.5%. A quarter reported visiting a dentist for professional cleaning once a year, and 42.6% reported brushing their teeth 3 or more times per day.

Over 10 years, 16% had a new diagnosis of diabetes.

In analyses adjusted for all confounding factors, the presence of gum disease was associated with a 9% increased risk of diabetes (hazard ratio 1.09, 95% CI 1.07 to 1.12).

Having 15 or more missing teeth was linked with 21% increased risk (HR 1.21, 95% CI 1.09 to 1.33).

Meanwhile, brushing teeth 3 or more times a day was linked with 8% decreased risk of diabetes (HR 0.92, 95% CI 0.89 to 0.95).


How did the researchers interpret the results?

The researchers conclude that frequency of tooth brushing was linked with decreased risk of diabetes and gum disease, and greater number of missing teeth with increased risk.



This is a novel analysis to have looked at the link between dental health and risk of diabetes, but it does not prove that one has directly caused the other.

There's a high possibility that other health and lifestyle factors are linked with both chance of poor dental health, and chance of diabetes, and this is underlying the links. The researchers have tried to account for several factors, but it's difficult to fully remove their influence while others may be having an effect. For example, the study has not assessed diet. People eating a high-sugar diet may have poorer dental health and higher chance of developing diabetes. Likewise people following a healthier lifestyle in general may take better care of their dental health.

The risk associations were very small – a relative risk increase (or decrease) of only a few per cent. So even if there is any direct link, this perhaps shows that other factors such as weight, diet and physical activity – and those we cannot change like family history – may have far greater influence on any individual's risk.

Other limitations include the restricted level of information available in the database. For example, one of the criteria for diagnosing diabetes was a one-off blood glucose measurement above 7.0mmol/l. You'd normally expect this to be repeated to confirm a diagnosis.

Also being a specific South Korean population, they may have many different health and lifestyle characteristics and baseline risk of diabetes (which is more common in Asian populations). Therefore the results may not be directly applicable to the UK.

Dentists in the UK also generally advise that you brush your teeth for 2 minutes twice a day, morning and night. The findings of this study do not seem to provide a strong basis on which to change this recommendation.

The best way to reduce your risk of diabetes is to follow a healthy diet, low in sugar and saturated fat, take regular physical activity and maintain a healthy weight.

Find out more about diabetes and how to keep your teeth clean.

Analysis by Bazian
Edited by NHS Website

Links to the headlines

Brushing your teeth THREE times a day could ward off diabetes as study finds those who exceed the twice-a-day recommendation have a 14% lower risk

Mail Online, 2 March 2020

Links to the science

Chang Y, Sung Lee J, Lee KJ, et al

Improved oral hygiene is associated with decreased risk of new-onset diabetes: a nationwide population-based cohort study

Diabetologia. Published online 2 March 2020