Participants reporting a daily sleep duration of eight hours or more including naps were 15 percent more likely to have metabolic syndrome. This relationship remained unchanged after full adjustment for potential confounders. Participants who reported a short sleep duration of less than six hours initially were 14 percent more likely to have metabolic syndrome; this association disappeared after controlling for potential confounders. Participants were 29,310 people 50 years of age or older in Guangzhou, China.