**3. Results**

Following keyword search, 53 articles in Medline/PubMed/Google Scholar and 5 in CINAHL database were found. Out of those, 48 studies met the inclusion criteria. Abstracts of all 48 studies were screened. Twenty-six studies were excluded for variety of reasons of being editorials, commentaries/letters, abstract-only study, combined vitamin E with other vitamins, focused on other form of dementia rather than MCI, reviews, narratives and opinion-based papers. Finally, 22 papers [19–41] were included in this review for the data summarization (Figure 1). Characteristics of finally included studies are provided in Table A1 in Appendix A. *Healthcare* **2021**, *9*, x FOR PEER REVIEW 4 of 12

**Figure 1.** Flow diagram of the literature search and selection process. **Figure 1.** Flow diagram of the literature search and selection process.

Of 22 finally included studies, seven were conducted with animals. Out of seven, six studies conducted on rats, mice, and other animals exhibited some level of the neuroprotective effect of vitamin E by lowering the rate or delaying cognitive impairment progression. Similarly, out of 15 studies conducted on humans, eight studies reported Vitamin Of 22 finally included studies, seven were conducted with animals. Out of seven, six studies conducted on rats, mice, and other animals exhibited some level of the neuroprotective effect of vitamin E by lowering the rate or delaying cognitive impairment progression. Similarly, out of 15 studies conducted on humans, eight studies reported

fect in improving learning and memory functions. Two studies of each experimental and double-blind randomized placebo-controlled did not find any effect of Vitamin E on cognitive impairment while a clinical study14 suggested a potentially favorable effect (Table

> **May be Effective**

**Suggest Further** 

**Exploration No Effect** 

**Improved Learning and Memory Functions** 

(*n* = 4) 2 2

**Table 2.** Summary results of all studies in the review (*n* = 22).

Mice (*n* = 2) 1 1

2 1

Clinical (*n* = 2) 2 1

2 & Table A1).

Rats (*n* = 3) 3

(*n* = 2) <sup>2</sup>

(*n* = 1) <sup>1</sup>

(*n* = 1) <sup>1</sup>

**Delay or A Lower Rate of Cognitive Decline or Neuroprotective Effect** 

**Categories** 

Other animals

Cross-sectional

Case-control

Cohort (prospective) (*n* = 3)

Experimental

Animals

Human

Vitamin E's role in lowering the risk or delaying cognitive impairment. Two studies, one cohort and a double-blind randomized placebo-controlled study, demonstrated Vitamin E's effect in improving learning and memory functions. Two studies of each experimental and double-blind randomized placebo-controlled did not find any effect of Vitamin E on cognitive impairment while a clinical study14 suggested a potentially favorable effect (Tables 2 and A1).


**Table 2.** Summary results of all studies in the review (*n* = 22).
