Study Suggests Periodontal Disease Bacteria May Be Linked to Depression

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It’s common knowledge that poor dental health may lead to serious systemic complications when left untreated. However, scientists have gathered groundbreaking evidence that suggests advanced stages of periodontal disease can also affect a patient’s mental health. The Journal of Clinical Periodontology recently published an article titled “Periodontal diseases and depression: A pre‐clinical in vivo study” that further explored this theory.

A Closer Look at Depression

According to the World Health Organization, depression is a mental health disorder that affects over 260 million people around the world. Statistics from the National Institute of Mental Health reveal that an estimated 17.3 million adults in America experienced at least one major depressive episode a year. Women are more likely to be clinically diagnosed with depression than men.

Depression is typically placed into three categories: mild, moderate, or severe. While a severe depressive episode may cause someone to have delusions or suicidal thoughts, a person suffering from a mild depressive episode may experience noticeable mood fluctuations or have difficulty completing routine tasks.

Mental health disorders can stem from various social, psychological, and biological factors. Death, divorce, financial stress, and other traumatic life events can greatly increase someone’s chances of developing depression.

Some of the most common symptoms associated with depression include:

  • Feelings of hopelessness
  • Insomnia
  • Changes in appetite or weight
  • Apathy
  • Anxiety
  • Less energy
  • Trouble concentrating
  • Suicidal thoughts
  • Reckless behavior
  • Physical aches and pains

The rate of depression and other mental disorders is on the rise due to inadequate healthcare coverage, lack of mental health education, and the social stigma surrounding seeking mental health treatment.

Those who do seek professional help may be able to overcome their depressive episodes by pursuing psychological and pharmacological treatments as well as changing their diet, frequent exercise, and other healthy habits.

About the Study

Researchers María Martínez and David Martín‐Hernández conducted a study to investigate the link between poor dental health and depression. Martínez is currently pursuing her Postgraduate program in Periodontology at the Complutense University in Madrid, Spain. While, Martín‐Hernández works in the Department of Pharmacology and Toxicology as a member of the Faculty of Medicine at the same university. Together with their team of scientists, the academics decided to analyze how the microbiological, behavioral, and molecular levels of periodontitis may cause depression using a pre‐clinical in vivo model.

They gathered 48 lab rats in total and separated them into four groups of twelve. The researchers induced periodontitis by introducing the bacteria Porphyromonas gingivalis and Fusobacterium nucleatum into their oral cavity. By the end of three months, periodontitis had formed. Of the four groups, one was a control group, while another had periodontitis and spent another three weeks adding elements that would add chronic mild stress. While another group had periodontitis without the additional chronic mild stress, and another group had the stress without periodontitis.

Once they had prepared the rats, they used analysis of variance (or ANOVA) tests to examine their behavior to look for signs of depression, alveolar bone levels, and periodontal clinical variables. They also measured their microbial counts and expression of inflammatory mediators in the plasma and brain frontal cortex.

In Conclusion

At the end of the study, Martínez and Martín‐Hernández discovered that the bacteria Fusobacterium nucleatum can cause neuroinflammation and link the periodontal disease to depression. The group of lab rats with periodontitis and chronic mild stress showed the highest expression of pro‐inflammatory mediators in the brain’s frontal cortex. The same group also experienced an interruption of their hypothalamic-pituitary–adrenal stress axis, along with an increase in plasma corticosterone and glucocorticoid receptor levels. The researchers state, “Neuroinflammation induced by F. nucleatum (through a leaky mouth) might act as the linking mechanism between periodontal diseases and depression.”

Though this is a small, in vivo study, it shows the need for further research into the oral-brain health link. Just as a healthy mouth is a healthy body, it might also be able to be said that a healthy mouth can lead to, or help with, a healthy mind.

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