*2.1. Search Strategy*

Bibliographical databases, including Medline (PubMed), CINAHL, and Google Scholar were quickly searched in January/February 2020. Pharmacological synonyms of vitamin E were used as related terms to locate potential evidence to be included in this review. Articles related to cognitive impairment were also sought using the Boolean operator "AND" to narrow down search results to include articles containing the specified terms. A detailed list of key words is shown in Table 1.


**Table 1.** List of keywords used for literature search.
