PTH and metabolic syndrome: After adjusting for potential confounders including age, smoking status, drinking status, exercise status, region of residence, seasonality, and parathyroid hormone level, the lowest 25(OH)D quartile group was associated with a higher risk of MetS (odds ratio [OR] 2.25, 95% confidence interval [CI] 1.48–3.43 in men and OR 1.65, 95% CI 1.27–2.16 in women) compared to the highest 25(OH)D quartile group as the reference group.