Associations between sleep problems and the occurrence of gastroesophageal reflux disease (GERD) among 7,857 twins.

OR, odds ratio; CI, confidence interval.aThe different numbers of GERD cases for the four sleep exposures are due to different numbers of missing observations in the sleep questions.bORs adjusted for age, sex, educational level, body mass index, and tobacco smoking.cThe insomnia index was constructed by combining the three different sleep problem questions and 0 points were given for “seldom”, 1 point for “sometimes” and 2 points for “often”. The highest scores, 4–6 points or if the participant had answered “often”, were then classified as “often having sleep problems”, 1–3 points as “sometimes having sleep problems” and 0 as ”seldom having sleep problems”.