Effect of vitamin D supplementation on sexual function in women with type 2 diabetes: Study protocol for a randomized, double-blind, placebo controlled clinical trial

Abstract

Background

Female sexual dysfunction (FSD) is a common and often overlooked complication of type 2 diabetes, adversely affecting quality of life and marital satisfaction. It involves vascular, neurological, hormonal, and psychological mechanisms. Vitamin D deficiency, prevalent among individuals with type 2 diabetes, is associated with metabolic disturbances, endothelial dysfunction, and may contribute to impaired sexual function. Although some studies in healthy women with low vitamin D levels suggest benefit, evidence on its effect in women with type 2 diabetes is limited.

Methods

This randomized, double-blind, placebo-controlled clinical trial investigates whether weekly vitamin D supplementation improves sexual function in reproductive-age women with type 2 diabetes. One hundred eligible participants will be randomly allocated (1:1) to receive either vitamin D (50,000 IU) or placebo weekly for 12 weeks. The primary outcome is change in total Female Sexual Function Index (FSFI) score from baseline to week 13. Secondary analyses will explore relationships with glycemic control (HbA1c and fasting blood sugar), body mass index (BMI), and demographic factors. Women with severe stress, anxiety, or depression, as assessed by the Depression, Anxiety and Stress Scale (DASS-21), will be excluded. Compliance will be monitored via weekly follow-up, and analyses will follow the intention-to-treat principle using appropriate statistical tests at a significance level of 0.05.

Discussion

This trial will provide evidence on the effectiveness of vitamin D supplementation in improving sexual function among women with type 2 diabetes, potentially offering a safe and cost-effective approach to enhance metabolic and sexual health.

Trial registration

Iranian Registry of Clinical Trials, IRCT20150624022896N3 (registered 2024-02-27).

Highlights

• •Assessing weekly 50,000 IU Vitamin D vs. placebo on female T2DM sexual function.
• •Double-blind trial with hidden block randomization and strict screening (N = 100).
• •Exclusion of severe psychological disorders yields a purer assessment of Vitamin D effect.
• •Protocol registered (IRCT) emphasizing robust ethical oversight and patient consent.

1. Introduction

Sexual activity is one of the most important aspects of human life, which can be influenced by individual characteristics, interpersonal relationships, family and socio-cultural conditions, the environment and context of sexual activity of the individual and their partner, physical and mental health, and hormonal status [1]. Sexual health is a key factor in marital stability and a major determinant of couples' happiness and overall quality of life [2]. Neglecting sexual desire can have irreparable effects on individuals. Physical and psychological stress resulting from low sexual satisfaction may lead to sexual dysfunction and health problems [3]. Female sexual dysfunction (FSD) is a distressing condition affecting many women worldwide [4]. This disorder is not a single issue but a combination of various adverse conditions, including low sexual desire, arousal disorders, orgasmic disorders, and sexual satisfaction and pain during intercourse [5]. FSD affects 41% of women of reproductive age globally, making it a highly prevalent medical problem [6]. Although FSD is a common health issue, discussing it remains taboo, particularly in Eastern societies [7]. Women are often reluctant to talk about sexual issues or seek help due to social and cultural constraints [8]. The hemodynamic characteristics of the external genitalia and vagina play an important role in providing adequate blood flow, which primarily influences peripheral arousal and lubrication [9]. Any vascular impairment of the clitoris and vagina can lead to FSD due to reduced lubrication, decreased vaginal stimulation and arousal, and increased dyspareunia, potentially affecting orgasm and sexual satisfaction as well [10,11]. Recent studies have shown that peripheral sexual response in women is a vascular-dependent event and that vascular function of the genitalia can be affected by metabolic changes [12]. Hormonal, neurological, vascular, psychological factors, certain diseases, some surgical procedures, or medications may contribute to decreased sexual desire [13]. Medical conditions such as diabetes, hypothyroidism, Addison's disease, Cushing's disease, temporal lobe lesions, menopause, coronary artery disease, heart failure, renal failure, stroke, and HIV may reduce sexual desire [14]. Sexual dysfunction is a common chronic complication of diabetes, which may arise from vascular complications or autonomic neuropathy [[15], [16], [17]]. Cardiovascular risk factors, including hypertension, metabolic syndrome, dyslipidemia, obesity, and insulin resistance, may be associated with FSD [9,11,18]. Available data indicate a relationship between FSD and dysmetabolic conditions such as diabetes mellitus [18]. Due to its complexity and socio-cultural factors, FSD has been less studied compared to male sexual dysfunction [11]. Studies have shown that the prevalence of sexual dysfunction is higher in diabetic patients than in the general population [[19], [20], [21], [22]]. Sexual dysfunction in women with diabetes includes inadequate lubrication, decreased sexual desire, painful intercourse (dyspareunia, vulvodynia), orgasmic disorders, and vaginismus [23,24]. In women with type 2 diabetes, the prevalence of sexual dysfunction by domain is reported as follows: desire disorder 70%-82%, arousal problems 54%-68%, inadequate vaginal lubrication 33%-66%, orgasmic disorders 33%-84%, and pain 33%-46% [25]. Low vitamin D levels are also associated with an increased risk of both central and peripheral neuropathy. Since genital blood flow is regulated through the hormonal and nervous systems, vitamin D may improve related dysfunctions via its effects on these systems [26]. Studies have demonstrated that vitamin D supplementation in women with severe vitamin D deficiency (levels <10 ng/ml) significantly improves sexual desire, orgasm, and sexual satisfaction, as well as overall FSFI scores. In contrast, in women with insufficient vitamin D levels (10–30 ng/ml), only sexual desire shows improvement [27]. regimens providing at least 600,000 international units of ergocalciferol have been identified as the most effective strategy for achieving vitamin D sufficiency [28]. Various therapeutic regimens exist; in this study, a weekly dose of 50,000 IU of vitamin D for 12 weeks is used [29,30]. Given the high prevalence of FSD in women with type 2 diabetes and the potential role of vitamin D in sexual function, this study aims to investigate the effect of weekly vitamin D supplementation on sexual function in this population.

2. Material and methods

2.1. Research setting and design

This randomized, double-blind (participants and researchers), controlled clinical trial will involve 100 women with type 2 diabetes. Participants will be recruited from the Endocrinology and Metabolism Research Center and a designated laboratory in Isfahan, Iran. The study population will comprise women of reproductive age diagnosed with type 2 diabetes mellitus who attend the Endocrinology and Metabolism Research Center and its affiliated laboratory for diagnostic tests and therapeutic interventions. Eligible women meeting the inclusion criteria will be enrolled as the study sample.

2.2. Intervention and control

The intervention group will receive twelve 50,000 IU vitamin D pearls manufactured by Tehran Daru Pharmaceutical Company, administered as one pearl per week. The control group will receive twelve placebo pearls, identical in appearance and coating to the vitamin D pearls, also produced by Tehran Daru Pharmaceutical Company, administered as one pearl per week.

2.3. Inclusion and exclusion criteria

2.3.1. Inclusion criteria

Married women aged 18 to 49 years who do not have any conditions that may result in sexual dysfunction will be included in the study. Participants must be free from multiple sclerosis and other central nervous system disorders, psychiatric conditions, intellectual disabilities, vasculitis, uncontrolled hypo- or hyperthyroidism, anatomical genital tract abnormalities, tumors, masses, or cancer, according to their medical records [31]. Additionally, women taking medications known to affect sexual function (e.g., H2 receptor blockers, hypnotics, cardiovascular drugs, anticonvulsants, narcotics, chemotherapeutic agents, corticosteroids, antihistamines, opioids, alcohol, psychotropic substances, or barbiturates) will be exclude [31]. Women's health status must also include absence of endometriosis [32], no erectile dysfunction in their spouses [33], basic literacy, and no self-reported history of alcohol or cigarette addiction [34].

Researchers ensure that participants are oriented to time and place, obtain their full consent and willingness to participate in the study. Participants’ diagnosis of type 2 diabetes mellitus for at least one year will be confirmed through medical records or physician referral. Women must not have taken vitamin D supplementation for at least three months prior to enrollment. Only those with normal serum calcium, phosphorus, and albumin levels [35], a body mass index (BMI) below 30 [36], and no history of malabsorption disorders will be eligible [37].

2.3.2. Exclusion criteria

Women will be excluded if they are.

• 1.Pregnant or within the first three months postpartum [38];
• 2.Have a history of oophorectomy, hysterectomy, or mastectomy [39];
• 3.Experience premature menopause (age <40 years) [40].

The withdrawal criteria include separation of the couples during the study period, unwillingness to continue participation, death of either partner, or the onset of a severe illness during the study.

2.4. Informed consent process

Following a preliminary introduction in alignment with the research objectives, the researcher obtains written informed consent from participants before the intervention, either through telephone or in-person contact. Participation in the study is entirely voluntary, and participants can withdraw from the study at any time if they are no longer willing to continue.

2.5. Sampling method

Convenience sampling will be employed based on inclusion criteria. Specifically, the names of women diagnosed with diabetes who either had an active medical record at the Isfahan Endocrinology and Metabolism Research Center or presented to its laboratory are extracted from the archive system, resulting in a list that contains their names and contact numbers. Subsequently, potential participants are contacted by telephone, receiving information such as an introduction of the researcher and the study objectives. Women who meet the inclusion criteria and express their willingness to participate in the study are enrolled accordingly.

2.6. Sample size estimation

Based on a Type I error rate of 0.05, statistical power of 0.80, and reference data from a prior study [41], the minimum required sample size will be 50 participants per group. Thus, 100 women are selected as the total sample size, accounting for an anticipated 30% dropout rate.

$$n=\frac{2{\left(Z_{1-\alpha /2}+Z_{1-\beta }\right)}^2{\sigma }^2}{{ϵ}^2}$$

2.7. Randomization and blinding

Randomization is done using the permuted block randomization method with a block size of four, and the sequence is generated using the online tool Sealed Envelope [42]. To establish the sequence for participants’ allocation to groups, a randomized block design with permuted blocks of size four and an allocation ratio of 1:1 will be employed, through which an independent individual not involved in the study will generate the randomization sequence using the online tool Sealedenvelope.com. The intervention type for each participant will be recorded on cards following a predetermined sequence and placed in opaque, coded envelopes to ensure allocation concealment. The intervention and placebo medications are identical in appearance and distributed to participants by the center secretary, who remains blinded to the intervention content and follows the assigned allocation codes. Using a double-blind design throughout the study ensures that neither the participants nor the researchers are aware of the intervention assignments. A collaborator blinded to group allocations will collect the required data, which will undergo analysis using only group codes and without knowledge of the intervention types.

2.8. Administration of intervention

Eligible female participants listed in the qualified candidate roster will be contacted by the research team following referral to the Isfahan Endocrinology and Metabolism Research Center and the designated laboratory. Appointments will be scheduled for participants to visit the center. Upon arrival, participants will receive a detailed briefing on the study objectives. Written informed consent will be obtained either in-person or via telephone prior to any study procedures.

Interviews are conducted in private and appropriate settings to collect demographic and clinical data, including age, educational level, employment status, duration of diabetes diagnosis, type of diabetes treatment, current medication use, height, weight, and body mass index (BMI), as well as reproductive history (number of pregnancies, deliveries, abortions, living children, intrauterine deaths, and deceased children). Fasting blood glucose (FBS) and glycated hemoglobin (HbA1c) are also recorded as relevant metabolic parameters.

Participants will complete the DASS-21 questionnaire to assess levels of depression, anxiety, and stress. Women scoring above the thresholds for severe symptoms—depression >20, anxiety >14, and stress >25—will be excluded from the study and referred to a psychiatrist for further evaluation and management. Those within the acceptable ranges will proceed with enrollment.

Serum vitamin D levels will be measured at the Isfahan Endocrinology Center laboratory. Participants with serum vitamin D levels <10 ng/mL or >100 ng/mL will be referred to an endocrinologist for further evaluation and management. Women with insufficient serum vitamin D levels (10–30 ng/mL) will be enrolled in the study. Additionally, serum calcium, phosphorus, and albumin will be measured using the remaining serum samples, which will be stored at the research center's freezer until analysis. Reference ranges are as follows:

Calcium, 8.6–10.2 mg/dL (2.2–2.6 mmol/L);

Albumin, 3.5–5.5 g/dL (35–55 g/L, SI units);

Phosphorus, 3–4.5 mg/dL (0.97–1.45 mmol/L, SI units).

Only participants with normal levels of these markers will complete the Female Sexual Function Index (FSFI) questionnaire. Measurement of calcium and phosphorus ensures that participants have normal mineral metabolism, as vitamin D status directly influences calcium absorption and serum mineral balance [43]. while assessment of albumin allows for correct interpretation of calcium levels because a substantial portion of circulating calcium is protein-bound [44].

Participants in both the intervention and control groups will be advised to expose their face, hands, feet, and lower back to sunlight without sunscreen for 5–30 min at least twice a week, between 10:00 a.m. and 4:00 p.m., as a general guideline for maintaining adequate vitamin D levels [45]. Follow-up assessments will occur at week 13 after study initiation. Participants will undergo serum vitamin D measurement and complete the FSFI questionnaire in a designated private area within the research facility to ensure confidentiality and standardized data collection.

2.9. Intervention description

2.9.1. Intervention and control groups

The intervention group will receive 12 pearls of vitamin D supplement (50,000 IU each), manufactured by Tehran Daru Pharmaceutical Company and distributed by the research center coordinator. Participants will be instructed to take one vitamin D pearl weekly after lunch.

The control group will receive 12 placebo pearls, also produced by Tehran Daru Pharmaceutical Company, identical in appearance and coating to the vitamin D supplements. These are similarly distributed by the research center coordinator, with instructions for participants to take one placebo pearl weekly after lunch.

2.9.2. Intervention fidelity

The researcher conducts weekly telephone follow-ups with participants to ensure participants’ compliance with the supplementation and placebo regimen.

2.10. Measurement of the primary and additional outcomes

2.10.1. Sexual function scores at baseline and week 13 post-intervention

The present study uses FSFI questionnaire to measure and compare FSFI (Female Sexual Function Index) scores at baseline and week 13 following the initiation of the study in the intervention and control groups.

2.11. Methods and data collection instruments

Demographic and clinical data, including age, educational level, employment status, duration of diabetes, type of diabetes treatment, current medication use, height, weight, and body mass index (BMI), as well as reproductive history variables such as number of pregnancies, deliveries, miscarriages, living children, stillbirths, and deceased children, are recorded through structured interviews using a standardized questionnaire. Fasting blood glucose (FBS) and glycated hemoglobin (HbA1c) are also recorded as metabolic parameters.

The Female Sexual Function Index (FSFI) questionnaire is utilized to assess female sexual function. The FSFI comprises subscales, including desire (question 1-2 of the original questionnaire, with a cut-off score of 3.3), psychological arousal and excitement (question 3-6, cut-off 3.4), lubrication (question 7-10, cut-off 3.4), orgasm (question 11-13, cut-off 3.4), satisfaction (question 14-16, cut-off 3.8), and sexual pain (question 17-19, cut-off 3.8). The overall cut-off score for the total FSFI scale is 26.5, with scores exceeding this threshold indicating good sexual function [46]. The Persian version of the FSFI questionnaire used in this study is known as FSFI-IV and has been translated, validated, and confirmed for reliability [47].

The standardized Depression Anxiety Stress Scales (DASS-21) questionnaire will be employed to assess stress, anxiety, and depression [48]. This instrument comprises three subscales measuring stress, anxiety, and depression. Participants are required to report the extent to which they experienced each symptom over the past week, rating each item on a 4-point Likert scale from 0 ("Did not apply to me at all") to 3 ("Applied to me very much or most of the time"). Severity scores on the DASS-21 range from 0 to 28 for depression, 0 to 20 for anxiety, and 0 to 33 for stress. Specifically, each of the three subscales includes seven items – depression, anxiety and stress. Higher scores on each subscale highlight greater severity of stress, anxiety, or depression, and the overall score is derived by summing the individual subscale scores. The validity and reliability of the Persian version of this instrument are confirmed in the present study [49].

2.12. Data collection and storage

Participants who meet the study inclusion criteria will be randomly assigned to either the intervention group (vitamin D supplement) or the control group (placebo), with 50 participants in each group, according to a predetermined random sequence. The intervention group will receive one vitamin D pearl (50,000 IU) weekly for 12 weeks, while the control group will receive one identical placebo pearl weekly for the same duration. The Female Sexual Function Index (FSFI) questionnaire will be completed at two time points: baseline (prior to the intervention) and at week 13. Questionnaires will be self-administered by participants under the supervision of a trained researcher to ensure completeness, accuracy, and adherence to the study protocol. All data will be collected in a coded format, with no identifiable information linked to participant responses. Paper forms will be initially used for data collection and will subsequently be entered into a secure electronic database. Only authorized members of the research team will have access to the data, and all stages of data storage and management will comply with confidentiality principles and research ethics guidelines. The Ethics Committee will monitor the data collection process to ensure protocol adherence and participant safety.

2.13. Data analysis

All outcomes in this study are quantitative and continuous, measured using score-based scales. Data will be entered and analyzed using SPSS version 27. Quantitative variables will be reported as mean ± standard deviation (SD) or median and interquartile range (IQR), depending on data distribution, while categorical variables will be presented as frequency and percentage. The normality of continuous variables will be assessed using the Shapiro–Wilk test. Between-group comparisons will be conducted using independent t-tests or Mann–Whitney U tests, as appropriate. Within-group comparisons from baseline to week 13 will be performed using paired t-tests or Wilcoxon signed-rank tests. Categorical variables will be compared using chi-square tests. Analysis of covariance (ANCOVA) will be employed to control for baseline differences, including initial FSFI scores and other relevant covariates. A significance level of 0.05 will be applied for all statistical tests.

2.14. Adverse event reporting

Any unexpected or unintended adverse events occurring during the intervention period, such as symptoms of vitamin D toxicity, will be carefully documented by the research team. Participants experiencing adverse events will receive appropriate medical evaluation and management, and the events will be reported promptly to the Ethics Committee. All procedures related to adverse event monitoring, reporting, and management will be conducted in accordance with institutional guidelines and ethical standards.

2.15. Patient and public involvement

Patients and public representatives were involved in the development of this study protocol. Previously published research on patient priorities, experiences, and preferences guided the formulation of the research question and outcome measures. Participants will have access to study findings through publications in peer-reviewed journals and presentations at relevant research conferences. Additionally, feedback from participants during the pilot phase was used to refine study procedures, improve questionnaire clarity, and ensure feasibility of intervention administration.

3. Discussion

Sexual function is a critical component of marital satisfaction and overall quality of life. Diabetes itself adversely affects sexual function through vascular alterations and neuropathic damage, which can disrupt clitoral engorgement, vaginal lubrication, and overall genital arousal, resulting in dyspareunia and reduced sexual satisfaction [50,51]. Moreover, diabetes can disturb the balance of sex hormones, including estrogen and testosterone, further diminishing sexual desire and overall satisfaction. Female sexual function is influenced by multiple hormones. Estrogens are essential for maintaining mucosal integrity, sensory perception, and genital blood flow, which are critical for sexual desire and arousal. Androgens, particularly testosterone, regulate sexual desire, arousal, orgasm, and overall sexual pleasure. Testosterone deficiency can lead to decreased vaginal lubrication, impaired genital blood flow, reduced responsiveness to sexual stimuli, dyspareunia, lower sexual motivation, persistent fatigue, depressed mood, diminished sexual pleasure, and, in some cases, sexual aversion [52,53]. In women with type 2 diabetes, sexual dysfunction is a prevalent concern due to metabolic, vascular, and hormonal disturbances associated with the disease. Vitamin D plays a vital role in the regulation of insulin secretion by binding to vitamin D receptors (VDRs) expressed in pancreatic beta cells. Extracellular calcium, which is modulated by vitamin D, is essential for proper insulin release. Furthermore, vitamin D enhances insulin sensitivity in multiple tissues by upregulating insulin receptor expression and increasing the translocation of glucose transporter type 4 (GLUT-4), thereby facilitating glucose uptake by cells [54]. These metabolic effects are particularly relevant in women with diabetes, as improved glycemic control can indirectly influence sexual function by enhancing vascular and nerve health. In addition to its metabolic effects, vitamin D exerts anti-inflammatory actions by downregulating pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), which contributes to the reduction of chronic low-grade inflammation commonly observed in diabetes. Vitamin D also promotes the secretion of adiponectin, an adipokine that enhances insulin sensitivity. By mitigating inflammation and modulating lipid metabolism and adipogenesis, vitamin D may improve vascular function and reduce insulin resistance. Moreover, research indicates that vitamin D may enhance endothelial nitric oxide production, further supporting vascular health and tissue perfusion [55]. Low vitamin D status is associated with an increased risk of atherosclerosis, coronary artery disease, reduced serum testosterone concentrations, lower free androgen index, and a higher likelihood of both autonomic and peripheral neuropathies. Given the involvement of vitamin D in hormonal regulation and neural function, deficiency may impair genital blood flow, potentially leading to sexual dysfunction [26]. Previous studies support the beneficial effects of vitamin D on sexual function and mood. Krysiak et al. (2018) demonstrated that vitamin D supplementation improved sexual functioning and mood in young women with low vitamin D levels. Their findings revealed a positive correlation between serum vitamin D levels and both sexual health and reduced depressive symptoms, emphasizing the integral role of vitamin D in overall well-being, particularly in women with deficiency. The current study is grounded in evidence suggesting that vitamin D supplementation can improve sexual function, particularly in women with insufficient or deficient vitamin D levels [27]. Because baseline vitamin D status is an important consideration in the design and interpretation of vitamin D randomized controlled trials, the present study specifically enrolled women with insufficient baseline serum 25(OH)D concentrations (10–30 ng/mL) [56] This study aims to investigate the effect of vitamin D supplementation on sexual function in women with type 2 diabetes. By targeting this population, the study aims to elucidate the potential therapeutic role of vitamin D in mitigating diabetes-related sexual dysfunction and improving overall quality of life.

Several limitations should be considered when interpreting the findings of this trial. Although diabetes duration was recorded, diabetic complications were not systematically assessed; therefore, the potential influence of diabetes-related complications, particularly vascular and neuropathic complications, on sexual function could not be fully evaluated. Although serum calcium, phosphorus, and albumin were assessed, serum magnesium and parathyroid hormone (PTH) were not measured because of financial constraints. Therefore, the study could not comprehensively assess all factors related to mineral metabolism and vitamin D physiology. In addition, although blood pressure and heart rate were routinely assessed as part of the clinical evaluation at the study site, these parameters were not prespecified study variables and were not systematically recorded in the study dataset. Consequently, their potential contribution as cardiovascular confounding factors could not be formally evaluated. In addition, although current medication use was recorded as part of the demographic assessment, dietary habits, nutritional intake, and the use of supplements other than vitamin D were not systematically assessed. Therefore, the potential influence of dietary and other nutritional factors on vitamin D status and sexual function could not be fully evaluated. This limitation is relevant to nutrient-based clinical trials because co-nutrient status may influence the response to a nutrient intervention [57].

4. Trial status

The study protocol (Version 1) was approved by the Research Ethics Committee of the School of Medicine, Isfahan University of Medical Sciences on 27 December 2023. Participant recruitment took place from 30 September 2025 to 1 February 2026. The intervention for all participants started on 2 February 2026 and is expected to be completed by 27 April 2026. The trial is registered in the Iranian Registry of Clinical Trials (IRCT) with registration number IRCT20150624022896N3, registered on 27 February 2024.

CRediT authorship contribution statement

Fatemeh Shakouri Joubani: Writing – original draft, Conceptualization, Methodology. Maryam Kianpour: Writing – review & editing, Supervision, Project administration, Methodology, Conceptualization. Mansour Siavash: Writing – review & editing, Methodology, Conceptualization.

Ethics declaration

Written informed consent to take part in the study and to publish the article has been obtained from all participants or their legal representatives. The privacy rights of participants have been observed.

This study was performed in compliance with relevant laws, regulatory frameworks and guidelines where the research took place. This study was approved by the Isfahan University of Medical Sciences. (Approval No. IR.MUI.MED.REC.1402.361)

The results of this clinical trial and any associated work have been posted in a registry. This clinical trial was registered with number 20150624022896N3 (Iranian Registry of Clinical Trials).

Ethics approval

The present study has been approved by the Ethics Committee of Biomedical Research at Isfahan University of Medical Sciences (Approval Code: IR.MUI.MED.REC.1402.361). The study is also registered in the Iranian Registry of Clinical Trials (IRCT) with the registration number IRCT20150624022896N3. In addition, the necessary introduction letters have been obtained from the University's Vice Chancellor for Research and the Faculty of Nursing and Midwifery, and subsequently submitted to the Endocrinology and Metabolism Research Center. All participants are required to complete written informed consent. Participation in the study is entirely voluntary, and participants may withdraw at any time without any consequences.

All participants are assured that their information will remain confidential. Accordingly, in the absence of consent, questionnaires are completed anonymously, identified only by a code number rather than by name. Throughout the study, all necessary laboratory tests are performed free of charge for the participants. Women with serum vitamin D levels >100 ng/ml or <10 ng/ml are excluded from the study and referred to a specialist for appropriate treatment. At the end of the study, to ensure equity between groups, vitamin D supplements will be provided to participants in the control group who have low vitamin D levels. The results of this study will be submitted to the Vice Chancellor for Research at Isfahan University of Medical Sciences and other relevant authorities. No professional writer or commercial editor will be involved in the preparation of the manuscript. All authors contributed to the conception, design, drafting, and final approval of the manuscript. Any substantial amendments to the study protocol including changes to eligibility criteria, primary or secondary outcomes, or analysis methods will be communicated to all investigators, the Ethics Committee, the clinical trial registry, and participants when necessary, after obtaining Ethics Committee approval. The authors wish to express their gratitude to all participants for their involvement in the study. Finally, all participants will attend a free group counseling session at the end of the study.

Trial registration

Iranian Registry of Clinical Trials, IRCT 20150624022896N3.

Registered 2023-12-27, https://irct.behdasht.gov.ir/user/trial/74645/view.

Confirmed in IRCT: 2024-02-27.

Consent for publication

As no identifiable information from the participants has been reported in the article, obtaining consent for publication is neither required nor applicable.

Funding

Funding has been obtained from Research Council of Isfahan University of Medical Sciences , Iran approved 21 January 2024 with Grant no. 3402560. This protocol in peer review process has undergone full external peer review by Isfahan University of Medical Sciences (funding body).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Access to the final study data will be restricted to the principal investigator, research team members, and the supervisor of the Ethics Committee. There are no contractual or administrative restrictions on access for these authorized individuals.