Background: Reports on the possible risks for Alzheimer’s disease (AD) have included tooth loss as a potential risk factor. However, there are few studies addressing the association between tooth loss and AD in a large sample of participants. Accordingly, the objective of the current study was to explore the association of tooth loss with the development of AD in Korean adults. Methods: This nested case–control study, which is an analysis utilizing the data of the Korean National Health Insurance Service Health Screening Cohort study, randomly selected AD and control participants among Korean residents aged ≥60 years. The association between the number of missing teeth and AD occurrence was examined using a logistic regression model. Participants’ lifestyle factors (smoking and alcohol consumption) and various medical conditions and comorbidities were included as covariates. Results: The mean number of missing teeth was 2.94 in the AD group and 2.59 in the control group. After adjusting for covariates, tooth loss was significantly associated with AD, with an odds ratio (OR) (per 16 missing teeth) of 1.15 (95% confidence interval (CI) = 1.07–1.23, p < 0.001). Conclusions: Tooth loss remained consistently significantly associated with an increased risk of AD for both upper and lower tooth loss. A higher number of missing teeth was related to a higher probability of AD occurrence in an elderly Korean population. Efforts to manage tooth loss could be a possible approach to prevent AD.

Previous studies have reported the association of obesity with increased morbidity or mortality due to the coronavirus disease 2019 (COVID-19). This study aims to investigate the relationship of obesity, as defined by the body mass index (BMI), with morbidity and mortality due to COVID-19. Data from 5628 confirmed COVID-19 patients were collected by the Centers for Disease Control and Prevention of Korea. The hazard ratios (HRs) for mortality in the BMI groups were analyzed using the Cox proportional hazard model adjusted for covariates. The odds ratios (ORs) of morbidity and diabetes in the BMI groups were analyzed using logistic regression adjusted for the same covariates. Both underweight and obesity were associated with a higher HR for mortality (adjusted HR = 2.28, 95% confidence intervals [95% CI] = 1.23–4.25, p = 0.009 for underweight and adjusted HR = 1.71, 95% CI = 1.10–2.66, p = 0.017 for obese). Obesity was related to higher odds of morbidity (adjusted OR = 1.71, 95% CI = 1.32–2.21, p < 0.001). Underweight and obesity were associated with high mortality and/or morbidity due to COVID-19 in Korea.

Background: Although the dopaminergic system is interconnected with the hypothalamic-pituitary-thyroid axis, few studies have explained the causal relationship between thyroid disease and Parkinson’s disease (PD). Objective: The goal of this study was to investigate the association between thyroid diseases and PD in Korean residents. Methods: The Korean National Health Insurance Service-National Sample Cohort, which includes individuals aged ≥40 years, was assessed from 2002 to 2015. A total of 5,586 PD patients were matched by age, sex, income, and the region of residence with 22,344 control participants at a ratio of 1:4. In the PD and control groups, previous histories of levothyroxine treatment, goiter, hypothyroidism, thyroiditis, and hyperthyroidism were investigated. Results: The rates of levothyroxine treatment for more than 3 months, hypothyroidism, and hyperthyroidism were higher in the PD group than the control group (3.2%, 3.8%, and 2.8% vs. 2.5%, 2.9%, and 1.9%, respectively, p < 0.05). The adjusted odds ratios (ORs) in model 2, which was adjusted for all potential confounders, for hypothyroidism and hyperthyroidism in the PD group were 1.25 (95% confidence interval (CI) 1.01–1.55, p = 0.044) and 1.37 (95% CI 1.13–1.67, p = 0.002), respectively. In subgroup analyses, the association between hypothyroidism and PD was maintained in men older than 70 years and the association between hyperthyroidism and PD was maintained in women younger than 70 years. Conclusion: Both hyperthyroidism and hypothyroidism were associated with higher risk of PD, particularly for women younger than 70 years and men older than 70 years, respectively.

This study aimed to evaluate the association between asthma and the intake of coffee/green tea/soda. We used Health Examinee data from the Korean Genome and Epidemiology Study (2004–2016). The participants (n = 3146 with asthma; n = 158,902 non-asthma) were asked about the frequency and amount of their coffee/green tea/soda intake. Multiple logistic regression analyses were used to calculate the adjusted odds ratios (aORs) with 95% confidence intervals (CIs) for asthma according to the frequency and amount of coffee/green tea/soda intake. Compared to the group consuming no coffee, the aORs for asthma were 0.82 (95% CI = 0.73–0.93, p = 0.002) in the group consuming coffee 1–2 times/day and 0.87 (95% CI = 0.78–0.97, p = 0.011) in the group consuming coffee in quantities of 1 cup, respectively. However, the frequency and amount of green tea and soda consumption were not significantly associated with asthma after adjusting for coffee consumption (all p > 0.05). These findings were consistent in the female subgroup (1–2 times/day: aOR = 0.76, 95% CI = 0.66–0.87, p < 0.001, and 1 cup each time: aOR = 0.79, 95% CI = 0.70–0.90, p < 0.001) but not in the male subgroup. Drinking 1 cup of coffee each time and 1–2 times per day may have protective effects against asthma in a Korean population. However, the associations between asthma and green tea/soda cannot be clearly established.