Effect of vitamin E supplementation on uterine cervical neoplasm: A meta-analysis of case-control studies

Risk factors for the development of cervical cancer: analysis of the evidence

Introduction

Cervical cancer (CC) is the fourth most prevalent female cancer globally. Understanding its epidemiology is crucial for devising practical strategies suited to geographic and social contexts to attain the global eradication of CC. Hence, this study examined the latest evidence of risk factors contributing to CC development.

Methods

An independent literature search was conducted on PubMed using MESH terms. The primary sources were meta-analyses published from 2010 to 2023, which detail updated evidence on risk factors associated with CC. Additionally, the quality of the evidence was evaluated using the GRADE system and recommendations were made accordingly.

Results

The main risk factors related to the cause of CC include co-infections with other sexually transmitted infections, genetic markers, cervicovaginal microbiota, nutritional factors, comorbidities that affect the immune response, smoking, and the use of hormonal contraceptives with a quality evidence based on the GRADE scale moderate.

Conclusions

Since the necessary cause for CC is persistent cervicovaginal HPV, all the risk factors implicated in the causality of CC act as non-independent cofactors that increase the risk of CC. Thus, changes in public policies aimed at addressing these risk factors are highly recommended and can substantially decrease the risk of CC.

Vitamins in Gynecologic Malignancies

The combination of vitamin A and D derivatives with classical chemotherapeutic treatments results in more satisfactory outcomes. The use of drug combinations, such as 9cUAB130 with carboplatin and cisplatin with TAC-101, shows enhanced cytotoxic effects and reductions in ovarian tumor volume compared to single-drug treatments. Combining cisplatin with calcitriol and progesterone increases VDR expression, potentially enhancing the effectiveness of anticancer therapy in ovarian cancer. The effectiveness of vitamin derivatives in anticancer treatment may vary depending on the characteristics of the tumor and the cell line from which it originated. An increase in thiamine intake of one unit is associated with an 18% decrease in HPV infection. Higher intake of vitamin C by 50 mg/day is linked to a lower risk of cervical neoplasia. Beta-carotene, vitamin C, and vitamin E are associated with risk reductions of 12%, 15%, and 9% in endometrial cancer, respectively. A balanced daily intake of vitamins is important, as both deficiency and excess can influence cancer development. It has been observed that there is a U-shaped relationship between group B vitamins and metabolic markers and clinical outcomes.

Vitamin D and Its Receptors in Cervical Cancer

Several studies have investigated the relationship between vitamin D (VD) and its receptors (VDR) and the risk of cervical cancer. However, the underlying mechanisms that underpin these associations remain incompletely comprehended. In this review, we analyzed the impacts of VD and VDR on cervical cancer and related mechanisms, and discussed the effects of VD, calcium, and other vitamins on cervical cancer. Our literature research found that VD, VDR and their related signaling pathways played indispensable roles in the occurrence and progression of cervical cancer. Epidemiological studies have established associations between VD, VDR, and cervical cancer susceptibility. Current studies have shown that the inhibitory effect of VD and VDR on cervical cancer may be attributed to a variety of molecules and pathways, such as the EAG potassium channel, HCCR-1, estrogen and its receptor, p53, pRb, TNF-α, the PI3K/Akt pathway, and the Wnt/β-catenin pathway. This review also briefly discussed the association between VDR gene polymorphisms and cervical cancer, albeit a comprehensive elucidation of this relationship remains an ongoing research endeavor. Additionally, the potential ramifications of VD, calcium, and other vitamins on cervical cancer has been elucidated, yet further exploration into the precise mechanistic underpinnings of these potential effects is warranted. Therefore, we suggest that further studies should focus on explorations into the intricate interplay among diverse molecular pathways and entities, elucidation of the mechanistic underpinnings of VDR polymorphic loci changes in the context of HPV infection and VD, inquiries into the mechanisms of VD in conjunction with calcium and other vitamins, as well as investigations of the efficacy of VD supplementation or VDR agonists as part of cervical cancer treatment strategies in the clinical trials.

Vitamin E - a scoping review for Nordic Nutrition Recommendations 2023

Current evidence suggests that dietary vitamin E (as α-tocopherol) intake has a beneficial role in preventing certain chronic diseases. In contrast, there is no clear evidence for the benefit of α-tocopherol supplements in a generally healthy population. Deficiency symptoms are rare and mainly occur due to genetic or other factors affecting α-tocopherol absorption and/or metabolism, rather than a low α-tocopherol intake. No qualified systematic review was identified by the NNR2023 project for updating the dietary reference values (DRV).

Association between Dietary Vitamin E Intake and Human Papillomavirus Infection among US Adults: A Cross-Sectional Study from National Health and Nutrition Examination Survey

Persistent high-risk human papillomavirus (HPV) infection is responsible for most genital, anal, and oropharyngeal cancers, in which men contribute significantly to infection and subsequent tumorigenesis in women. Vitamin E has been shown to be associated with vaginal HPV infection and cervical cancer. However, the association of vitamin E consumption with HPV infection among the overall population remains unclear. We investigate the association between vitamin E consumption and genital and oral HPV infection in both men and women. We used cross-sectional data from the National Health and Nutrition Examination Survey between 2013 and 2016 to collect details on their dietary vitamin E intake, genital and oral HPV infection status, and other essential variables. In total, 5809 participants aged 18-59 years were identified, with overall prevalence of high-risk and low-risk HPV infection of 23.7% and 21.1%, respectively. Compared with the lowest vitamin E group Q1 (<5.18 mg/day), the adjusted OR for vitamin E consumption and overall high-risk HPV infection in Q2 (5.18-7.54 mg/day), Q3 (7.55-10.82 mg/day), and Q4 (>10.82 mg/day) were 0.91 (95% CI: 0.81-1.03, p = 0.134), 0.77 (95% CI: 0.69-0.87, p < 0.001), and 0.72 (95% CI: 0.65-0.80, p < 0.001), respectively. Restricted cubic spline regression showed a linear relationship between vitamin E consumption and overall high-risk HPV infection. This linear relationship also existed for vitamin E consumption and overall low-risk HPV infection. After being stratified by gender and site, vitamin E consumption was inversely related to vaginal low- and high-risk HPV infection, penile high-risk HPV infection, and male oral low-risk HPV infection. In conclusion, we identified inverse linear relationships between dietary vitamin E intake and overall high- and low-risk HPV infection. Future well-designed longitudinal studies are still required to validate the impact of vitamin E on HPV carcinogenesis.

Risk factors for human papillomavirus infection, cervical intraepithelial neoplasia and cervical cancer: an umbrella review and follow-up Mendelian randomisation studies

BACKGROUND

Persistent infection by oncogenic human papillomavirus (HPV) is necessary although not sufficient for development of cervical cancer. Behavioural, environmental, or comorbid exposures may promote or protect against malignant transformation. Randomised evidence is limited and the validity of observational studies describing these associations remains unclear.

METHODS

In this umbrella review, we searched electronic databases to identify meta-analyses of observational studies that evaluated risk or protective factors and the incidence of HPV infection, cervical intra-epithelial neoplasia (CIN), cervical cancer incidence and mortality. Following re-analysis, evidence was classified and graded based on a pre-defined set of statistical criteria. Quality was assessed with AMSTAR-2. For all associations graded as weak evidence or above, with available genetic instruments, we also performed Mendelian randomisation to examine the potential causal effect of modifiable exposures with risk of cervical cancer. The protocol for this study was registered on PROSPERO (CRD42020189995).

RESULTS

We included 171 meta-analyses of different exposure contrasts from 50 studies. Systemic immunosuppression including HIV infection (RR = 2.20 (95% CI = 1.89-2.54)) and immunosuppressive medications for inflammatory bowel disease (RR = 1.33 (95% CI = 1.27-1.39)), as well as an altered vaginal microbiome (RR = 1.59 (95% CI = 1.40-1.81)), were supported by strong and highly suggestive evidence for an association with HPV persistence, CIN or cervical cancer. Smoking, number of sexual partners and young age at first pregnancy were supported by highly suggestive evidence and confirmed by Mendelian randomisation.

CONCLUSIONS

Our main analysis supported the association of systemic (HIV infection, immunosuppressive medications) and local immunosuppression (altered vaginal microbiota) with increased risk for worse HPV and cervical disease outcomes. Mendelian randomisation confirmed the link for genetically predicted lifetime smoking index, and young age at first pregnancy with cervical cancer, highlighting also that observational evidence can hide different inherent biases. This evidence strengthens the need for more frequent HPV screening in people with immunosuppression, further investigation of the vaginal microbiome and access to sexual health services.

Vitamin E and Multiple Health Outcomes: An Umbrella Review of Meta-Analyses

The relationship between vitamin E intake or circulating α-tocopherol and various health outcomes is still debatable and uncertain. We conducted an umbrella review to identify the relationships between vitamin E intake or circulating tocopherol and health outcomes by merging and recalculating earlier meta-analyses. The connections that were found to be statistically significant were then classified into different evidence levels based on p values, between-study heterogeneity, prediction intervals, and small study effects. We finally included 32 eligible meta-analyses with four vitamin E sources and 64 unique health outcomes. Only the association between circulating α-tocopherol and wheeze or asthma in children was substantiated by consistent evidence. Suggestive evidence was suggested for seven results on endothelial function (supplemental vitamin E): serum C-reactive protein (CRP) concentrations (supplemental vitamin E), cervical cancer (dietary vitamin E), esophageal cancer (dietary vitamin E), cervical intraepithelial neoplasia (CIN, dietary vitamin E), pancreatic cancer (total vitamin E intake), and colorectal cancer (circulating α-tocopherol levels); all of these showed a protective effect consistent with the vitamin E source. In conclusion, our work has indicated that vitamin E is protective for several particular health outcomes. Further prospective studies are required when other factors that may contribute to bias are considered.

Vitamin E intake and multiple health outcomes: an umbrella review

Background

The benefits of vitamin E (VE) for multiple health outcomes have been well evaluated in many recent studies.

Objective

The purpose of this umbrella review was to conduct a systematic evaluation of the possible associations between VE intake and various health outcomes.

Methods

We systematically searched various databases, such as PubMed, Embase, and the Web of Science, to identify related meta-analyses of observational studies and randomized trials. We estimated the effect size of each association by using the random or fixed effects models and the 95% confidence intervals. We used standard approaches to evaluate the quality of the articles (AMSTAR) and classified the evidence into different levels of quality (GRADE).

Results

A total of 1,974 review articles were searched, and 27 articles with 28 health outcomes were yielded according to our exclusion criteria. The intake of VE was inversely associated with the risk of breast cancer, lung cancer, esophageal cancer, gastric cancer, pancreatic cancer, kidney cancer, bladder cancer, cervical neoplasms, cardiovascular disease, Parkinson's disease, depression, age-related cataracts, metabolic syndrome, and fracture. Overall, most of the quality of the evidence was low or very low. Three outcomes (stroke, age-related cataracts, obesity) were identified as having a "moderate" level of quality. The AMSTAR scores for all health outcomes ranged from 5 to 10.

Conclusion

Our study revealed that VE intake is beneficially related to multiple health outcomes. However, future studies on recommended doses and recommended populations of VE are also needed.

Systematic review registration

http://www.crd.york.ac.uk/PROSPERO/, identifier: CRD42022339571.

Non-Genetic Factors and Risk of Cervical Cancer: An Umbrella Review of Systematic Reviews and Meta-Analyses of Observational Studies

Objectives: The association between non-genetic risk factors and cervical cancer (CC) remains controversial and unclear. This umbrella review was conducted to evaluate and synthesize previously published systematic reviews and meta-analyses related to non-genetic factors and CC risk.

Methods: We searched PubMed, Web of Science, and EMBASE to identify studies investigating the association between extragenetic factors and CC risk. For each article, we calculated the summary effect size and the 95% confidence interval. Specific criteria were used to classify the association into four levels: strong, highly suggestive, suggestive, or weak.

Results: A total of 18 meta-analyses of different risk factors for CC were examined; these studies covered risk factors related to diet, lifestyle, reproduction, disease, viral infection, microorganisms, and parasites. Oral contraceptive use and Chlamydia trachomatis infection were shown to increase CC risk, and this was supported by strong evidence. Additionally, there were four risk factors supported by highly suggestive evidence and six risk factors supported by suggestive evidence.

Conclusion: In conclusion, there is a strong association between oral contraceptive use, Chlamydia trachomatis infection, and increased CC risk.

Antioxidants Associated With Oncogenic Human Papillomavirus Infection in Women

BACKGROUND

Human papillomavirus (HPV) infection is a major cause of cervical cancer. Studies showed the onset of HPV carcinogenesis may be induced by oxidative stress affecting the host immune system. The association between antioxidants and oncogenic HPV remains unclear. In this study, we aim to identify antioxidants associated with vaginal HPV infection in women.

METHODS

The associations between the 15 antioxidants and vaginal HPV infection status (no, low-risk [LR], and high-risk [HR] HPV) were evaluated using 11 070 women who participated in the 2003-2016 National Health and Nutrition Examination Survey (NHANES).

RESULTS

We identified serum albumin and 4 dietary antioxidants (vitamin A, B2, E, and folate) inversely associated with HR-HPV infection. Women with a low level of albumin (≤39 g/L) have a significantly higher risk of HR-HPV (odds ratio [OR] = 1.4, P = .009 vs >44 g/L). A Nutritional Antioxidant Score (NAS) was developed based on these 4 dietary antioxidants. The women with the lowest quartile NAS had a higher chance of HR-HPV (OR = 1.3, P = .030) and LR-HPV (OR = 1.4, P = .002) compared with the women with the highest quartile NAS.

CONCLUSIONS

We identified 5 antioxidants negatively associated with vaginal HR-HPV infection in women. Our findings provide valuable insights into understanding antioxidants' impact on HPV carcinogenesis.

Role of Vitamin E in Selected Malignant Neoplasms in Women

Vitamin E, which is actually a mixture of eight isoforms (four tocopherols and four tocotrienols), is a powerful antioxidant that protects polyunsaturated fatty acids against oxidation and has the ability to break the chain lipid peroxidation, which is used in the treatment of heart disease, atherosclerosis, muscle disorders or infertility among men. Studies in-vitro show that one of the effects of tocopherol is the reduction of cancer stem cell activity which is connected to poor clinical course. In the scientific literature, reports on the participation of vitamin E not only in protection against the mutagenic effects of reactive oxygen species, but also in its anti-angiogenic activity and the ability to inhibit the invasion and metastasis of neoplastic cells are increasingly common. In this context, the role of vitamin E in preventing the neoplastic process and selected malignant neoplasms among women seems to be of particular interest. In this article, we present the results of research on the potential anticancer effects of vitamin E in the fight against breast, cervical, endometrial and ovarian cancer.

Nutrition in Gynecological Diseases: Current Perspectives

Diet and nutrition are fundamental in maintaining the general health of populations, including women's health. Health status can be affected by nutrient deficiency and vice versa. Gene-nutrient interactions are important contributors to health management and disease prevention. Nutrition can alter gene expression, as well as the susceptibility to diseases, including cancer, through several mechanisms. Gynecological diseases in general are diseases involving the female reproductive system and include benign and malignant tumors, infections, and endocrine diseases. Benign diseases such as uterine fibroids and endometriosis are common, with a negative impact on women's quality of life, while malignant tumors are among the most common cause of death in the recent years. In this comprehensive review article, a bibliographic search was performed for retrieving information about nutrients and how their deficiencies can be associated with gynecological diseases, namely polycystic ovary syndrome, infertility, uterine fibroids, endometriosis, dysmenorrhea, and infections, as well as cervical, endometrial, and ovarian cancers. Moreover, we discussed the potential beneficial impact of promising natural compounds and dietary supplements on alleviating these significant diseases.

The Role of Vitamin E in Breast Cancer Treatment and Prevention: Current Perspectives

Background:

Regarding the multifactorial etiology of breast cancer, food choices, as well as dietary intake, are the main modified factors in cancer prevention. In this sense, understanding molecular pathways involved in breast cancer proliferation can help determine the mechanisms of action of organic compounds such as antioxidant vitamins that are known to protect against cancer.

Objective:

Assess the mechanism of action of vitamin E in breast cancer modulation, with emphasis on important markers of tumor development.

Methods:

It is a systematic review carried out in PubMed and Web of Science databases, from the last 5 years, in Portuguese, English and Spanish. The following terms were selected according to The Medical Subject Headings (MeSH): “breast cancer” OR “breast neoplasms”, “tocopherol” OR “tocotrienols” OR “vitamin E”, as equated terms.

Results:

A total of 595 articles were found and 25 were selected according to inclusion criteria. Vitamin E has been related to suppression/overexpression of important tumorigenic pathways, mainly associated with proliferation, energy metabolism, chemosensitivity and invasion/metastasis. Clinical studies of vitamin E supplementation are needed to assess the dose/response effect on breast cancer patients.

Conclusion:

The safety of vitamin E supplementation is still controversial due to current studies design available. However, when vitamin E is supplemented, the dose and therapeutic regimen must be carefully decided, including the route of administration and breast cancer subtypes to enhance desired effects and minimize unwanted side effects.

Plasma, Prostate and Urine Levels of Tocopherols and Metabolites in Men after Supplementation with a γ-Tocopherol-Rich Vitamin E Mixture

The vitamin E forms γ- and δ-tocopherols (T) inhibit carcinogenesis in animal models; nevertheless, their cancer preventive activities in humans are uncertain. As an initial step to address this issue, we conducted a pilot phase 0 trial to determine the levels of tocopherols and their metabolites in prostate cancer patients undergoing radical prostatectomy. The patients were randomized to no supplementation or two capsules of a γ-T-rich vitamin E mixture daily for 7 or 14 day prior to prostatectomy. Blood and urine samples were collected before supplementation and on the day of surgery, along with prostate tissue, for analysis of tocopherols and their metabolites. Estimated blood loss during surgery was not significantly different across treatment arms and there were no reported adverse events. Prostate tissue levels of γ-T and δ-T were increased after 14 day of supplementation. Their side-chain degradation metabolites (CEHCs and CMBHCs) were significantly elevated in plasma, prostate and urine samples after supplementation for 7 or 14 day. In conclusion, supplementation with γ-T-rich vitamin E increased the prostate levels of γ-T and δ-T. The use of pure γ-T, δ-T or tocopherol mixtures with higher ratio of γ-T or δ-T to α-T is recommended for future studies.

Association of vitamin E on the risk of ovarian cancer: a meta-analysis

Many researches were conducted to assess the association of vitamin E intake on the risk of ovarian cancer, with conflict results. The current meta-analysis of published observational studies aimed to investigate the effect of vitamin E intake on ovarian cancer risk. The summary relative risks (RRs) with corresponding 95% confidence intervals (CIs) were calculated to measure the effectiveness of vitamin E intake on ovarian cancer risk using a random-effects model. As a result, 14 studies including 4597 patients were identified. Eleven studies reported about total vitamin E intake, eight studies about vitamin E intake from food only and five studies about vitamin E intake from supplement only on the risk of ovarian cancer. Overall, the summary RRs on ovarian cancer risk was 0.95 (95%CIs = 0.78–1.16) in total vitamin E intake, 0.99 (95%CIs = 0.77–1.27) in vitamin E intake from food only and 0.82 (95%CIs = 0.54–1.25) in vitamin E intake from supplement only. Results in subgroup analyses by study design and geographic location were consistent with overall result. In conclusions, the findings of this meta-analysis suggested that high intake of vitamin E from food or vitamin E supplement had no significant effect on the risk of ovarian cancer.

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols

α-Tocopherol (α-T) is the major form of vitamin E (VE) in animals and has the highest activity in carrying out the essential antioxidant functions of VE. Because of the involvement of oxidative stress in carcinogenesis, the cancer prevention activity of α-T has been studied extensively. Lower VE intake or nutritional status has been shown to be associated with increased cancer risk, and supplementation of α-T to populations with VE insufficiency has shown beneficial effects in lowering the cancer risk in some intervention studies. However, several large intervention studies with α-T conducted in North America have not demonstrated a cancer prevention effect. More recent studies have centered on the γ- and δ-forms of tocopherols and tocotrienols (T3). In comparison with α-T, these forms have much lower systemic bioavailability but have shown stronger cancer-preventive activities in many studies in animal models and cell lines. γ-T3 and δ-T3 generally have even higher activities than γ-T and δ-T. In this article, we review recent results from human and laboratory studies on the cancer-preventive activities of different forms of tocopherols and tocotrienols, at nutritional and pharmacological levels. We aim to elucidate the possible mechanisms of the preventive actions and discuss the possible application of the available information for human cancer prevention by different VE forms.

Dietary Inflammatory Index and Its Relationship with Cervical Carcinogenesis Risk in Korean Women: A Case-Control Study

Several studies have reported that diet’s inflammatory potential is related to chronic diseases such as cancer, but its relationship with cervical cancer risk has not been studied yet. The aim of this study was to investigate the association between Dietary Inflammatory Index (DII^®) and cervical cancer risk among Korean women. This study consisted of 764 cases with cervical intraepithelial neoplasia (CIN)1, 2, 3, or cervical cancer, and 729 controls from six gynecologic oncology clinics in South Korea. The DII was computed using a validated semiquantitative Food Frequency Questionnaire (FFQ). Odds ratios and 95% CI were calculated using multinomial logistic regression. Higher DII scores were associated with higher cervical carcinogenesis risk. A significant association was observed between the DII and risk among CIN2/3 [Odds Ratio (OR) = 3.14; 95% Confidence Intervals (CI) = 1.57–6.29] and cervical cancer patients (OR = 1.98; 95% CI = 1.01–3.88). Among Human Papilloma Virus (HPV)-positive women, a significant association was found between DII and cervical carcinoma risk with CIN2/3 (OR = 5.65; 95% CI = 1.38–23.2). Moreover, women with CIN2/3 and cervical cancer showed a significant association with proinflammatory diet in people without of physical activity (OR = 3.79; 95% CI = 1.81–7.93). These findings suggest that high intake of proinflammatory diets is associated with increased risk of cervical carcinogenesis among women with CIN2/3. Further evaluation in future studies to confirm this association is warranted.

The Relationship between the Serum Level of Selenium and Cervical Intraepithelial Neoplasia: A Comparative Study in a Population of Nigerian Women

Objective: To determine the relationship between the serum level of selenium and cervical intraepithelial neoplasia (CIN). Methods: A case controlled study that compared the serum level of selenium in 45 women with CIN (cases) to 45 women (age matched controls) with normal cervical cytology. Socio-demographic data and information on known risk factors for cervical cancer among the sample was compared between both groups using inferential statistics. Results: There was no significant difference in the mean selenium values between the cases and controls [p- 0.076, 95% CI (-15.08 – 0.76)]. However, subgroup analysis showed a statistically significant difference between patients with normal cervical cytology, CIN I, II and III (p= 0.021). In addition, there was also significant difference in the selenium level between women with normal cervical cytology and CIN III (p value = 0.016) with a significant inverse linear trend (p= 0.025). Conclusion: With increasing severity of CIN, a significant reduction in the level of selenium in serum was observed. This reducing value of serum selenium, a surrogate marker for increased oxidative stress, may be important factor for the development of persistent HPV infection and in particular high grade CIN III lesions. This observation requires further research.

Oxidative stress: therapeutic approaches for cervical cancer treatment

Oxidative stress results from an imbalance between the generation and elimination of oxidant species. This condition may result in DNA, RNA and protein damage, leading to the accumulation of genetic alterations that can favor malignant transformation. Persistent infection with high-risk human papillomavirus types is associated with inflammatory responses and reactive oxygen species production. In this context, oxidative stress, chronic inflammation and high-risk human papillomavirus can act in a synergistic manner. To counteract the harmful effects of oxidant species, protective molecules, known as antioxidant defenses, are produced by cells to maintain redox homeostasis. In recent years, the use of natural antioxidants as therapeutic strategies for cancer treatment has attracted the attention of the scientific community. This review discusses specific molecules and mechanisms that can act against or together with oxidative stress, presenting alternatives for cervical cancer prevention and treatment.

Higher serum zinc levels may reduce the risk of cervical cancer in Asian women: A meta-analysis

Objective

This meta-analysis was conducted to examine the possible association between serum zinc concentration and cervical cancer risk.

Methods

PubMed, WanFang, China National Knowledge Infrastructure, and SinoMed databases were searched for relevant articles published between January 1980 and September 2017. Results were combined using a random-effects model, and pooled standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated to compare serum zinc levels in patients with cervical cancer versus controls. Publication bias was evaluated using Begg’s funnel plot and Egger’s regression asymmetry test.

Results

Twelve articles regarding serum zinc levels and cervical cancer were included in this meta-analysis. Combined results showed that serum zinc levels in cervical cancer cases were significantly lower than in controls without cervical cancer (summary SMD –1.379, 95% CI –1.527, –1.231), with high heterogeneity (I² = 98.8%). Analysis of data stratified by geographic location showed a significant association between serum zinc levels and cervical cancer risk in Asian populations (summary SMD –1.391, 95% CI –1.543, –1.239).

Conclusions

Higher serum zinc levels may be a protective factor for cervical cancer in Asian women.