Background/Objectives: Erectile dysfunction (ED) is a common sexual disorder in men, frequently linked to endothelial dysfunction affecting penile vasculature. Accumulating evidence suggests that vitamin D (VD) status may influence endothelial function and, consequently, erectile function. VD deficiency has also been associated with cardiovascular risk factors, which are well-known contributors to ED. Methods: A systematic review following PRISMA guidelines was conducted, analyzing studies from PubMed and Cochrane databases published between 2010 and 2025. Randomized controlled trials, observational studies, and pilot clinical trials examining the relationship between VD levels and ED in the general male population were included. Results: Out of 1335 identified articles, 10 studies met inclusion criteria, encompassing over 13,000 men. Observational studies consistently showed that men with moderate-to-severe or arteriogenic ED had significantly lower serum VD levels and poorer erectile function scores compared to those with mild ED. VD deficiency was independently associated with higher ED prevalence, irrespective of lifestyle, cardiovascular risk, or sex hormone levels. Although several observational studies suggested a potential optimal vitamin D threshold, definitive recommendations cannot be established due to the heterogeneity of available evidence and conflicting findings from randomized controlled trials. The latter demonstrated inconsistent effects of vitamin D supplementation on erectile dysfunction outcomes, with the largest trial reporting no significant reduction in disease prevalence. These findings underscore the critical need for rigorously designed trials targeting populations with severe VD deficiency and arteriogenic ED. Conclusions: This systematic review highlights an association between vitamin D status and erectile dysfunction, particularly in men with moderate-to-severe or arteriogenic ED. However, most of the evidence is derived from low-certainty observational studies. While observational data suggest potential benefits of adequate VD levels for sexual health, well-designed randomized controlled trials are essential to delineate causal relationships and potential for therapeutic efficacy.

Background/Objectives: While it is known that Hashimoto’s thyroiditis (HT), goiter, thyroid nodules, and thyroid dysfunction may affect women’s reproductive health through hormonal and metabolic mechanisms, data are limited regarding the specific impacts on female sexual function. This study evaluated sexual function in women with thyroid disorders and examined its associations with thyroid function, age, menopausal status, and body mass index (BMI). Methods: A population-based survey was conducted in Kaunas, Lithuania, within the WHO MONICA framework. A random sample of 1569 women aged 25–69 years was included in the final analysis after applying the exclusion criteria. Anthropometric measurements were taken using standardized procedures, and the BMI was calculated. Sexual function was assessed using the 19-item Female Sexual Function Index (FSFI). Thyroid structure was evaluated by a team of trained physicians using ultrasound, while thyroid function was assessed via serum analysis (ELISA-based assays for TSH, fT4, and anti-TPO antibodies). Results: Of the 1569 women analyzed, 64.1% had sexual dysfunction (SD) (FSFI ≤ 26.55). Age and BMI showed significant negative correlations with all FSFI domains, with the strongest associations for arousal, lubrication, and total FSFI score (p < 0.01). SD was more prevalent among postmenopausal (43.6%) women than in premenopausal women (22.6%, p < 0.001) and increased with a higher BMI (p < 0.001). HT was found in 28.3% of participants. Compared with the reference group, women with HT were older, had higher BMI, higher TSH levels, and more hypothyroidism (p < 0.001). SD was more common in the HT group (71.7% vs. 64.2%, p < 0.001), with significantly lower lubrication and higher pain scores. In the multivariate analysis, only goiter remained an independent predictor of SD (p = 0.04). Conclusions: In conclusion, women with HT were older; had a higher BMI; and more frequently experienced SD, particularly reduced lubrication and increased pain, compared with the reference group. Although several thyroid conditions were associated with sexual dysfunction, only goiter remained an independent predictor after adjusting for age and BMI.