Effect of vitamin E supplementation on cardiometabolic risk factors, inflammatory and oxidative markers and hormonal functions in PCOS (polycystic ovary syndrome): a systematic review and meta‐analysis

Polycystic ovary syndrome (PCOS) is a common endocrinopathy among reproductive-age women. Various therapeutical approaches are currently used to manage or control symptoms associated with PCOS. This systematic review intended to assess the effects of Vit E supplementation on cardiometabolic risk factors, inflammatory and oxidative markers, and hormonal functions in PCOS women based on the clinical trial's results. The databases including PubMed, Scopus, Cochrane, Web of Science, and Embase were used to find all relevant studies. The authors reviewed all relevant clinical trials via systematic evaluation of abstracts and titles. Searches were conducted on August 1, 2020. After the initial search and reading of the article's title and abstract, 353 articles were reviewed; finally, 12 articles met the inclusion criteria. Vitamin E supplementation improves lipid profile, decreases insulin and HOMA-IR levels. Furthermore, while Vitamin E supplementation decreases LH and testosterone concentrations, it increases FSH and progestrone concentrations. The following meta-analysis showed that vitamin E supplementation made statistically significant improvements in triglyceride (TG) and low-density lipoproteins (LDL) levels, meanwhile, pooled mean difference for waist circumference (WC) and HOMA-IR were also statistically significant. Supplementary regimens containing vitamin E can positively affect metabolic and hormonal parameters in women with PCOS.


Inclusion criteria. Types of studies:
All relevant clinical trials (including double and single-blind and data from a parallel and cross-over group designed) evaluating the effects of vitamin E supplementary regimens in PCOS patients were gathered, and single-arm studies were not included in the study. Two authors (MM and GhT) independently screened all ofthe retrieved clinical trials using their titles and abstracts. Full-text of relevant articles were collected to assess their relevance according to the inclusion/exclusion criteria.

Types of participants:
The studies that evaluated the effects of vitamin E supplementation outcomes in the PCO adult population (≥ 18 years) were included in this study. In this regard, the subjects of the study contained patients with the PCOS receiving vitamin E supplementary regimens and control groups of PCOS patients receiving placebo or no treatment; we exclude those studies that have populations restricted to specific diseases or conditions.

Types of Interventions:
This systematic review study included all studies evaluating vitamin E supplementation (alone or as a part of combination therapy) in PCOS patients.

Types of outcomes:
The effects of vitamin E on the following outcomes were evaluated in PCOS patients: 1 Chen 22  Statistical analysis and data synthesis. The effects of vitamin E supplementation on cardiometabolic risk factors, inflammatory and oxidative markers, and hormonal functions in PCOS women were assessed using the standardized mean difference (SMD). The meta-analysis of SMD was performed and the outcome was demonstrated as pooled standardized mean difference with 95% confidence interval. The fixed and random effect models were considered for analysis based on homogeneity of data (I 2 < 50% considered as fix effect and I 2 ≥ 50% considered as a random effect). The publication bias was assessed using Egger test and was presented schematically using the funnel plot. Because of the scarcity of data subgroup analysis was not carried out on the extracted data.
Ethical considerations. In this study, ethical approval is not essential because used data are not subjects, and the results are discussed through peer-reviewed publications.

Results
Description of included studies. The flow chart of the search process and study selection is depicted in Fig. 1. Following a search on PubMed (n = 33), Scopus (n = 174), Web of Science (n = 54), and the Embase (n = 17) databases, 278 relevant articles were identified. After the initial search and reading of the article's title and abstract, 353 articles were reviewed; finally, 12 articles met the inclusion criteria 16 www.nature.com/scientificreports/ studies 2,15,17,22,24,25,28,34 . Three studies 2,22,34 did not report some outcomes after the intervention. One study 23 had a high risk of selective reporting bias as they did not report hormonal changes. The complete risk of bias evaluation is presented in Fig. 2. The GRADE framework 20,21 rated the strength of the evidence for all outcomes as moderate, except for BMI 16,23,24,26,27,[31][32][33] and weight 16,23,24,26,27,32 , which were rated as high; progesterone 24 , LH 24,26,29,31 , FSH 24,26,29,31 , and CRP 32,34 , which were rated as low; and CAT 28 and PRL 29 , which were rated as very low streng th (Table2 supplementary) .

Outcomes
Effect of vitamin E supplementation on sex hormones. Four studies evaluated testosterone levels pre and post Vitamin E co-supplementation (with magnesium, omega-3 FAs, and CoQ10). Table 2 shows all studies that showeda significant decrease in this regard in between the intervention group andthe control group. regarding the estradiol levels, two studies reported a similar increase in both intervention and control groups following vitamin E supplementation. In contrast, another studyreported no significant differences in estradiol levels following vitamin E + omega3 FAs supplementation. As shown on Table 2,only one study reported a small increase in estradiol levels with Vitamin E + CoQ10 supplemen group (d = -0.33) in comparison with the slight decrease that was observed in their control group (d = 0.21). Three studies evaluated Vitamin E's effect on

Effect of vitamin E supplementation on BMI, weight. Seven studies evaluated BMI changes, but only
two studies have shown significant albeit small decrease in BMI following vitamin E + CoQ10 supplementation. a study conducted in 2019 also reported a small significant decrease in waist circumference (d = 0.3). Changes in weight were not significant in either one of the studies that evaluated this concept.

Effect of vitamin E supplementation on Insulin resistance parameters. It has been hypothesized
that Vitamin E supplementation could affect insulin resistance parameters among patients with PCOS. All three studies have evaluated HOMA score and insulin level changes following dietary supplementation and have shown promising results ( Table 2). one of these studies showed a significant small decrease in HOMA score and insulin level (d = 0.15 and 0.2 respectively) in their vitamin E + magnesium supplemented study group 16   www.nature.com/scientificreports/ studies reported that CoQ10 supplementation with and without vitamin E led to a significant sizeable decrease in HOMA scores and insulin levels (d = 1.27 and 0.64 respectively); however, it was also emphasized that vitamin E supplementation alone did not have a similar impact. Only one study out of these three studies,. reported a significant decrease in FBS levels.

Effect of vitamin E supplementation on lipid profile. Vitamin E may also help PCOS patients by
improving their lipid profile. Three studies that evaluated cholesterol, LDL, and TG levels changes following Vit E supplementation showed promising results. As Table 2 shows, While one of the studies reports a small significant decrease in cholesterol, LDL, and TG levels (d = 0.19 and 0.09 and 0.27 respectively) in thevitamin E + magnesium supplemented study group, anotherstudy reports a significant moderate decrease in cholesterol, LDL, and TG levels following supplementation with vitamin E + CoQ10 (d = 0.4, 0.39, and 0.58 respectively). furthermore, another study claimed a moderate to huge decrease in cholesterol, LDL, and TG levels (d = 0.68 and 0.59 and 0.38) following vitamin E + Omega 3 fatty acid supplementation. Three studies evaluated HDL levels and only one reported beneficial effects for vitamin E + CoQ10 co-supplementation.

Effect of vitamin E supplementation on oxidative stress parameters.
Some studies have suggested vitamin E supplementations may have beneficial effects on oxidation biomarkers . Vitamin E supplementation was reported to lead to a significant increase in TAC in three studies and their respective cohen's d values is as the following: (d = -0.57), (d = -1.59) and (d = -0.8) ( Table 2). One study also reported a significant increase in catalase and glutathione levels and a significant decrease in malondialdehyde levels following supplementation with vitamin E plus omega-e fatty acids (d = -1.44, -0.57, and 1.23 respectively). From the data in Table 2, the two studies suggested a significant decrease in CRP levels (d = 0.33 and 0.2 respectively) and an increase in NO levels (d = -1.3 and -0.45) after supplementation with vitamin E + magnesium and vitamin E + omega-3 fatty acids.. All three studies evaluating MDA levels reported a medium to a large decrease in values following vitamin E supplementation. Considering GSH levels, while one of the studies reported a significant small increase in the vitamin E + magnesium supplemented group (d = -0.19), another failed to show any significant change.

Meta-analyses. Vitamin E and anthropometric indices. Fixed effect meta-analysis of eight included stud-
ies reported the effect of vitamin E on BMI. A pooled mean difference wasn't statistically significant (SMD: -0.17, CI: 95%:-0.95, 0.61) without heterogeneity (I 2 = 0%), which means vitamin E didn't improve BMI. Three articles investigated the effect of vitamin E on WC. A pooled mean difference was found to be significant (SMD: 3.38, 95% CI: 0.05-6.71) without heterogeneity (I 2 = 0%). Six studies demonstrated the effects of Vitamin E on weight, and the pooled mean difference compared with the placebo group was -0.86 (95%CI:-3.32,1.60) without heterogeneity (I 2 = 0%) (Fig. 3).

Discussion
The purpose of the current systematic review was to investigate the effects of vitamin E on cardiometabolic risk factors, inflammatory and oxidative markers, and hormonal function in PCOS patients. To our knowledge, this study is the first systematic review to assess the supplementary regimen role in PCOS treatment.
Vitamin E supplementation decreases testosterone and LH levels whereas it increases progesterone and FSH levels.  34 . and as the detrimental effects of high blood glucose levels on pancreatic islet cells have been linked to oxidative stress. Antioxidant supplementation could manage oxidative stress.
In regards to insulin resistance and dyslipidemia, Diamanti-Kandarakis suggested that insulin resistance can increase TG and LDL levels and decrease HDL levels in PCOS patients. Moreover, they proposed that   32 . A review and meta-analysis on the effects of omega-3 and vitamin E co-supplementation in patients with metabolic syndrome showed that this supplementary regimen could reduce both LDL and TG levels in these patients 34 .
There is a proposed mechanism for vitamin E's beneficial effects on lipid profile improvement, lipid peroxidation 36 and protection of LDL from oxidation. Niki E et al. have stated that Vitamin E's anti-oxidative feature is due to its beneficial effects on oxidative stress parameters [40].
The RCTs reviewed in this study showed a significant increase in TAC, NO, catalase, glutathione, GSH levels. they have also reported a substantial decrease in malondialdehyde, CRP, and MDA levels following supplementary regimen administration in PCOS patients. A study by Sepidarkish et al. showed vitamin E, and omega-3 fatty acid co-supplementation to have increased NO levels and TAC while decreasing MDA levels 32 .

Strengths and limitations.
This study is the first systematic review assessing the role of vitamin E supplementation in PCOS. In this systematic review, eligible studies couldn't control confusing residual variables. All of the Studies were adjusted for age and PCOS, but some of the reviews didn't consider well-defined risk factors for changing hormone levels.
This systematic review was unable to show inherent differences in vitamin E supplementation effects on PCOS between different populations and races. More studies evaluating the impact of supplementary regimens in various races and societies are needed. Moreover, due to the limited number of available studies ,we could not compare supplemental regimens' effects between different age groups. The reviewed studies have not pointed out www.nature.com/scientificreports/ as to whether their study populations had vitamin E deficiencies or not. Some studies have proposed that some of the beneficial effects of vitamin E supplementation might be limited to vitamin-E deficient people. Another limitation is that due to the focus of PROSPERO (International prospective register of systematic reviews) on COVID-19 registrations during the 2020 pandemic, The PROSPERO team has not checked the eligibility of our review.
Conclusions and implications for future research. We found that supplementary regimens containing vitamin E can positively affect the patients who are diagnosed with PCOS in regards to metabolic and hormonal parameters. It can improve their hormonal profile by decreasing testosterone and LH levels and by increasing progesterone and FSH levels. It can also reduce insulin resistance, cholesterol, LDL, and TG levels among these patients, it can also improve their cardio-metabolic profile. We also found that vitamin E supplementation can decrease oxidative stress in PCOS.
More studies are needed in order to evaluate the effects of vitamin E supplementation in different ethnicities and age groups. Other studies thatassess the effects of vitamin E supplementation in both vitamin E sufficient and deficient populations will add to current knowledge about the role of vitamin E supplementary regimens in PCOS.  www.nature.com/scientificreports/ Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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