Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting women of reproductive age and is characterized by a heterogeneous combination of reproductive, metabolic, and endocrine abnormalities. Menstrual dysfunction, hyperandrogenism, polycystic ovarian morphology, and metabolic disturbances are among its major clinical manifestations (1,2). Current international guidance emphasizes that PCOS is a complex condition with important reproductive, metabolic, psychological, and long-term health implications (3).

Infertility is a frequent reproductive consequence of PCOS and is predominantly related to ovulatory dysfunction. Abnormal follicular development, hyperandrogenism, insulin resistance, and altered gonadotropin signaling may contribute to impaired ovulation and reduced reproductive potential in affected women (4,5). The metabolic component of PCOS is also clinically important because insulin resistance and compensatory hyperinsulinemia may promote ovarian androgen production and further interfere with normal follicular maturation (6).

Vitamin D deficiency has been frequently reported among women with PCOS. Vitamin D receptors and vitamin-D-metabolizing enzymes are present in reproductive tissues, suggesting that vitamin D may have biological roles beyond calcium and bone metabolism (7,8). Vitamin D has been investigated in relation to ovarian steroidogenesis, follicular development, insulin sensitivity, inflammation, and reproductive function (9).

Several observational studies have reported lower serum 25-hydroxyvitamin D [25(OH)D] concentrations among women with PCOS, particularly among those with obesity and metabolic abnormalities (10). A potential relationship between vitamin D status and insulin resistance has also been proposed, although the strength and independence of this association remain uncertain because obesity and other metabolic factors may act as important confounders (11).

The possible relationship between vitamin D status and reproductive dysfunction has generated considerable interest. Some studies have reported associations between vitamin D deficiency and menstrual abnormalities, hyperandrogenism, impaired follicular development, and infertility, whereas other investigations have produced inconsistent findings (8,9,12). Differences in study populations, diagnostic criteria, vitamin D thresholds, obesity prevalence, and study design may partly explain these variations.

The issue is particularly relevant in South Asian populations, where PCOS, obesity, insulin resistance, and vitamin D deficiency may coexist frequently. Identifying clinical characteristics associated with vitamin D deficiency may therefore provide useful information during the assessment of women with PCOS and reproductive difficulties.

Therefore, the present study was conducted to determine the association between vitamin D deficiency and infertility among women with PCOS. The study also evaluated age, BMI, testosterone concentration, HOMA-IR, AMH concentration, and menstrual irregularity in relation to vitamin D status.

This observational study included 200 women with PCOS in the Department of Gynaecology and Obstetrics, Ayub Teaching Hospital Abbottabad, Khyber Pakhtunkhwa from December 2025 to May 2026. Demographic, anthropometric, biochemical, hormonal, and menstrual characteristics were recorded, including age, BMI, serum 25-hydroxyvitamin D concentration, vitamin D status, infertility status, testosterone, HOMA-IR, AMH, and menstrual irregularity. Vitamin D status was categorized according to the supplied dataset as deficient, insufficient, or sufficient. Infertility status was coded as 1 (infertile) or 0 (non-infertile), and menstrual irregularity as 1 (present) or 0 (absent). Continuous variables were summarized as mean ± standard deviation, while categorical variables were presented as frequencies and percentages. Differences across the three vitamin D categories were assessed using one-way analysis of variance for continuous variables and chi-square testing for categorical variables. For the principal analysis, participants with vitamin D deficiency were compared with those without deficiency; independent-samples tests were used for continuous variables and chi-square testing for categorical variables. The strength of association between vitamin D deficiency and infertility was expressed as an odds ratio with a 95% confidence interval. A p-value <0.05 was considered statistically significant.

A total of 200 women with PCOS were included. The overall mean age was 29.13 ± 3.22 years and mean BMI was 28.54 ± 4.45 kg/m². Overall, 106 (53.0%) women were vitamin-D deficient, 46 (23.0%) were insufficient, and 48 (24.0%) had sufficient vitamin D, as shown in Table 1.

Table 1. Distribution of participants according to vitamin D status.

Infertility was present in 112 (56.0%) participants. As shown in Table 2, 102/106 (96.2%) women with vitamin D deficiency were infertile, compared with 10/94 (10.6%) women without deficiency. The association was statistically significant (χ²=144.7, p<0.001). The crude odds ratio for infertility associated with vitamin D deficiency was 214.2 (95% CI 64.8–707.6).

Table 2. Association between vitamin D deficiency and infertility.

Clinical and biochemical characteristics differed across vitamin D categories for several measured variables. Table 3 presents the complete group-wise descriptive statistics and corresponding overall comparisons.

Table 3. Clinical, hormonal, metabolic, and reproductive characteristics according to vitamin D status. Values are mean ± SD unless otherwise indicated.

When women with vitamin D deficiency were compared with those without deficiency, substantial differences were observed in reproductive and metabolic characteristics. These comparisons are summarized in Table 4.

Table 4. Comparison of clinical, biochemical, and reproductive characteristics between women with and without vitamin D deficiency.

The present study demonstrated a marked association between vitamin D deficiency and infertility among women with PCOS. More than half of the study population had vitamin D deficiency, while infertility was present in 56.0% of participants. Notably, 96.2% of women classified as vitamin-D deficient were infertile compared with 10.6% of women without vitamin D deficiency. The crude odds ratio was 214.2 (95% CI 64.8–707.6; p<0.001). Vitamin D deficiency has been frequently described among women with PCOS, although prevalence varies according to population characteristics, season, body composition, laboratory methods, and the threshold used to define deficiency (13,14). The high prevalence observed in the present population is therefore consistent with the broader literature. A potential biological explanation involves interactions between vitamin D and ovarian as well as metabolic pathways. Vitamin D receptors are present in ovarian tissue, and experimental evidence suggests that vitamin D signaling may influence granulosa-cell function, follicular development, and steroidogenesis (15,16). Vitamin D may also interact with insulin signaling, providing a potential link between vitamin D status and the metabolic abnormalities frequently observed in PCOS (17). Insulin resistance is particularly relevant because it contributes to the metabolic phenotype of PCOS and may promote ovarian androgen production. Hyperinsulinemia can enhance androgen synthesis and interfere with normal follicular development, contributing to anovulation and infertility (18). Systematic reviews and meta-analyses have reported associations between vitamin D status and several PCOS characteristics, including insulin resistance, androgen concentrations, and menstrual dysfunction, although findings have not been entirely consistent (19,20). Some interventional studies have suggested possible improvements in selected metabolic or reproductive parameters following vitamin D supplementation, whereas other studies have reported heterogeneous or limited effects (21,22). The relationship between vitamin D and fertility should therefore be interpreted cautiously. Vitamin D deficiency may be a marker of an adverse metabolic phenotype rather than an independent cause of infertility. Obesity, physical inactivity, dietary factors, insulin resistance, and other PCOS characteristics may influence both vitamin D concentration and reproductive function (23). The very large association observed in the present dataset also requires careful interpretation. The exposure and outcome were highly concentrated in specific groups, resulting in a wide confidence interval around the odds ratio. Accordingly, the estimate should be regarded as a study-specific association rather than a universally applicable causal effect. Current international PCOS guidance emphasizes individualized assessment of reproductive and metabolic health rather than management of a single laboratory abnormality in isolation (24). Vitamin D status may therefore be assessed alongside BMI, glucose metabolism, menstrual function, androgen status, and fertility-related factors when clinically appropriate. Evidence that vitamin D supplementation improves fertility outcomes remains less definitive than evidence demonstrating frequent deficiency. Randomized trials and systematic reviews have reported variable effects on insulin resistance, androgen concentrations, menstrual characteristics, and reproductive outcomes (21,22,25). Correction of documented deficiency may be clinically appropriate, but the present observational study cannot establish that supplementation restores fertility. Menstrual irregularity is a common manifestation of PCOS and usually reflects ovulatory dysfunction. Previous investigations of the relationship between vitamin D status and menstrual cyclicity have produced heterogeneous results (20,26). The menstrual findings in the present study should therefore be interpreted as associations rather than evidence of a causal pathway. Strengths of this study include the sample of 200 women with PCOS and the availability of multiple reproductive, hormonal, metabolic, and anthropometric variables. Limitations include the observational nature of the dataset, absence of information on sunlight exposure, dietary vitamin D intake, physical activity, supplementation, socioeconomic factors, duration and etiology of infertility, and the limited ability to generalize findings beyond the study population. Overall, the findings demonstrate a strong association between vitamin D deficiency and infertility among women with PCOS in this study population. Prospective and interventional studies are required to determine whether correction of vitamin D deficiency independently improves reproductive outcomes.

Vitamin D deficiency was common among women with PCOS and showed a strong association with infertility in the present study. Women with vitamin D deficiency also demonstrated differences in several reproductive and metabolic characteristics. Because the study design does not establish causality, the findings should be interpreted as an association and should be confirmed in larger prospective and interventional studies.