For eight years, 265 older adults in Japan underwent routine examinations ranging from periodontal pocket depth to blood enzyme levels. The results were surprising: the more severe a person's periodontal condition, the greater the risk of elevated liver enzymes, which are markers of organ damage.
These findings came from a longitudinal study published in The Journal of Clinical Periodontology (2018), led by drg. Elastria Widita, MSc, PhD, a lecturer at the Faculty of Dentistry, Universitas Gadjah Mada, who was completing her doctoral research at Niigata University, Japan, at the time. Together with researchers from Niigata's Division of Preventive Dentistry, she investigated a question that has rarely been asked: can oral health serve as a reflection of liver health?
From the Gum Pocket to the Bloodstream
Periodontal disease is more than bleeding gums or bad breath. It is a chronic infection involving anaerobic Gram-negative bacteria that live deep within periodontal pockets and release lipopolysaccharide (LPS) into the bloodstream. Once LPS enters the circulation, the body responds by producing inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), which can damage tissues not only around the teeth but also in distant organs such as the liver.
This research was part of the Niigata Elderly Study, a community-based cohort study initiated in 1998 in Niigata City, Japan. The participants analyzed were independent older adults with a mean age of 72.5 years who did not require assistance with daily activities. Over eight years (2000–2008), they underwent annual periodontal examinations using a pressure-controlled probe with a force of 20 grams. Two primary parameters were measured: probing pocket depth (PPD) and clinical attachment level (CAL).
Meanwhile, liver enzyme levels—alanine transaminase (ALT) and aspartate transaminase (AST)—were measured at the beginning and end of the study period. ALT was selected as the primary marker because it is more specific for liver cell damage than AST, which is also found in skeletal muscle and the kidneys.
The Numbers Speak More Loudly
Logistic regression analysis showed that increased ALT levels were significantly associated with a greater number of sites with PPD ≥6 mm (odds ratio 1.10) and CAL ≥6 mm (odds ratio 1.03), even after the researchers controlled for potential confounding factors such as body mass index, HbA1c levels, triglycerides, albumin, exercise habits, and the number of remaining teeth. AST levels, meanwhile, showed no significant association with these periodontal parameters.
Even more interesting was the role of smoking. The researchers found a significant interaction between smoking status and the relationship between periodontal parameters and elevated ALT. Stratified analysis showed that among smokers, the risk of elevated ALT was substantially higher: OR 1.20 for PPD and OR 1.04 for CAL. Among non-smokers, however, these associations were not statistically significant.
“Increased ALT levels may be associated with clinical periodontal parameters in independently living Japanese older adults, and this association is modified by smoking status.”
The biological explanation is plausible. Smoking worsens the severity of periodontal disease while also triggering inflammatory gene activation and the production of reactive oxygen species (ROS), which damage cell membranes. The combination of these two factors—severe periodontitis and exposure to cigarette smoke—appears to create an environment more conducive to liver tissue damage.
Who Was Studied, and What Were the Limitations?
Of the 600 original participants in the Niigata Elderly Study, only 265 met all inclusion criteria and had complete data at both the beginning and end of the study. They consisted of 133 men and 132 women. During the eight-year observation period, 44% of the participants experienced increased AST levels, while 37% experienced increased ALT levels.
drg. Elastria Widita, MSc, PhD, and her team acknowledged several limitations. The study population consisted of independent older adults with a high level of functional capacity, meaning that the findings may not represent the general Japanese older population, let alone populations in other countries. In addition, precise alcohol intake was not measured, medication use was not assessed, and a history of hepatitis infection was not collected. The researchers were also unable to use C-reactive protein as an inflammatory marker because data were unavailable for most participants.
Nevertheless, the study also had clear strengths. Its eight-year longitudinal design provided insight into actual changes occurring in the body rather than merely offering a snapshot at a single point in time. The relative homogeneity of the Japanese population helped control for confounding factors such as race and sex, while stratified analyses based on smoking and alcohol consumption provided a deeper understanding of the findings.
The Mouth as a Window into Systemic Health
This study reinforces an increasingly prominent narrative in dental medicine: oral health does not exist in isolation. Periodontal bacteria such as Porphyromonas gingivalis do not merely damage the tissues supporting the teeth; these organisms can migrate to other organs, including the liver, and potentially trigger damage there.
For clinicians, these findings open the door to a more holistic approach to prevention. Controlling periodontal disease in older adults, particularly those who smoke, may not only be about saving teeth but also about helping maintain liver health. The question now shifts to how far periodontal interventions can reduce the risk of systemic organ damage. Larger prospective studies involving more diverse populations are still needed to answer this question.
Source DOI: DOI: 10.1111/jcpe.12861
Authors: Anny Anggraini; drg. Achmad Zam Zam Aghasy, M.Kes.
Photo: Freepik