Figure 1.

PRISMA flow-diagram of search process. The search strategy was initially conducted with three databases, although two studies were retrieved via handsearching and one study was retrieved from Natural Medicines. Following the removal of duplicate records (71), 463 records were screened. In total, 407 records were excluded based on title and abstract, and 56 full records were sought for retrieval. In total, 55 records were retrieved, of which 25 were excluded for various reasons. Briefly, 30 studies were ultimately included in the review, 13 studies assessing oral supplementation and 17 studies assessing topical application.