Frequency of tooth brushing as a predictive factor for future kidney function decline

Background Tooth brushing is important for maintaining oral health and preventing periodontal diseases (PDs), which commonly arise in patients with chronic kidney disease (CKD). However, the association between tooth brushing frequency and kidney function decline remains unclear. Methods We conducted a retrospective longitudinal study at St Luke’s International Hospital, Japan, and participants who underwent health examinations at the Centre for Preventive Medicine from 2005 to 2011 were included. Participants’ tooth brushing frequencies were assessed; multivariate analyses were conducted using a generalized estimating equation to evaluate the association between tooth brushing frequency and a composite renal outcome—composed of a 25% estimated glomerular filtration rate (eGFR) reduction, an eGFR of < 15 mL/min/1.73 m 2 , and a requirement for regular dialysis—after adjusting for potential covariates. We also stratified participants by baseline CKD risk category to perform sub-analyses. Results Overall, 76,472 participants were included (mean age of 45.9 years) and 38,233 (50%) were male. During follow-up, 8219 participants (10.8%) experienced composite renal outcomes. Brushing teeth at least once to twice a day was associated with significantly lower incidences of composite renal outcomes than brushing teeth less frequently (adjusted odds ratio [OR] 0.26; 95% confidence interval [CI] 0.24–0.28 for once to twice a day; adjusted OR 0.65; 95% CI 0.62–0.69 for after every meal). In our sub-analyses, brushing at least once to twice a day related to a decreased likelihood of composite renal outcomes; however, this effect was only observed within the low and moderate baseline risk groups. Conclusion Frequent tooth brushing benefits oral health and may be associated with slower kidney function decline, which could have implications for other systemic diseases. However, a longitudinal cohort study is required to confirm whether tooth brushing and overall oral health can haver a role in improving renal outcomes. Graphic abstract