Assessment of Study Quality included in the meta-analysis. 1

1. Representativeness of the exposed cohort; 2.Selection of the non-exposed cohort; 3.Ascertainment of exposure; 4.Demonstration that outcome of interest was not present at start of study; 5.Comparability of cohorts on the basis of the design or analysis; 6.Assessment of outcome; 7.Was follow-up long enough for outcomes to occur; 8.Adequacy of follow up of cohorts.2. Studies that controlled for age received one score, whereas studies that controlled for other important confounders received an additional score.3. Study with follow-up time>5 years was assigned one score.4. Study with follow-up rate>75% was assigned one score.