Population-based study of environmental/occupational lead exposure and amyotrophic lateral sclerosis: a systematic review and meta-analysis

Lead is a known risk factor for amyotrophic lateral sclerosis (ALS). However, the results of studies exploring the relationship between lead exposure and the occurrence of ALS are inconsistent. To clarify this issue, we conducted a systematic review and meta-analysis of relevant published articles on the relationship between lead exposure and the occurrence of ALS. We searched the PubMed, MEDLINE, Embase, and Science Direct databases for relevant publications. The quality of the articles was judged according to the Newcastle-Ottawa scale, and the meta-analysis was conducted using a random effect model. A total of 583 items were retrieved of which 11 case-control studies were selected. The ratio of maximal/minimal lead exposure yielded a pooled odds ratio (OR) of 1.46 (95% confidence interval (CI) 1.16-1.83) with moderate heterogeneity (I-2 = 51.8%; p = 0.019). Subgroup and sensitivity analyses showed stable results. There was evidence of publication bias, but the recalculated OR after employing the fill and trim method was 1.28 (95% CI 1.02-1.63). These results indicated that environmental/occupational lead exposure was positively proportional to the risk of ALS.