Prevalence and correlates of antinuclear antibodies in a Japanese community sample: a cross-sectional study

Background Antinuclear antibodies (ANA) are among the most commonly used tests in autoimmune disease but are frequently positive in healthy individuals, with uncertain significance. Reported prevalence ranges from under 6% to over 45% across populations, and its determinants in healthy individuals are poorly defined. Objective We examined ANA prevalence and its demographic and lifestyle correlates in a community sample in Japan. Methods Serum samples were obtained from 1,017 community residents in a single prefecture in Japan. Age and sex were recorded for all participants; smoking status and allergic history were available for a subset (n = 467). ANA were measured by indirect immunofluorescence on HEp-2 cells; a 1:40 titer defined positivity. Associations were assessed using chi-square tests, logistic regression with linear and quadratic age terms, and multivariable logistic regression adjusting sequentially for age, sex, smoking, and allergic history. Results Among 1,017 participants (542 women and 475 men), overall ANA positivity was 18.3% (186/1,017). Positivity was significantly higher in women than in men (21.8% vs. 14.3%) and showed a U-shaped age pattern in women. ANA positivity was not associated with allergic history. Exploratory subgroup analysis showed higher positivity in current or former smokers than never-smokers among men. After adjustment for age, female sex was independently associated with ANA positivity (OR 1.72, 95% CI 1.24–2.40). In the lifestyle subset, female sex was the only independently associated factor after adjustment for age, smoking status, and allergic history. Conclusions These data provide a population-specific baseline for ANA positivity in a Japanese community sample and confirm that prevalence is higher in women and varies with age. Because ANA is frequently measured and may precede autoimmune disease, longitudinal studies are needed to clarify whether incidental positivity in healthy individuals carries prognostic significance.