When we discuss fertility, we consider several factors. Still, one essential factor that often goes overlooked is Vitamin D. Many people focus on well-known factors like age, diet, and lifestyle. Still, there’s another crucial player in reproductive health that often flies under the radar: vitamin D. This is an essential nutrient that is often referred to as the sunshine vitamin, which plays a significant role in various bodily functions, including bone health, immune function, and most importantly, fertility.
It has been studied in several studies have shown that a deficiency in Vitamin D affects the fertility of both men and women. Therefore, it is crucial to comprehend the role of vitamin D in reproductive health and the steps that can be taken to enhance vitamin D levels. In this blog, we will delve into an understanding of Vitamin D deficiency and its link to Unexplained infertility.
Vitamin D plays a significant role in regulating hormones in both men and women. Its deficiency could affect a significant portion of reproductive age in women and is correlated with proper fertility outcomes. This includes cases associated with unexplained infertility where no proper cause of infertility is found after standard evaluations. Vitamin D helps in supporting immune function and mood regulation.
Studies show deficient women exhibit roughly 50% lower vitamin D biomarkers compared to fertile controls, with the lowest levels in unexplained infertility and PCOS patients. Correcting deficiencies through supplementation may enhance IVF success and sperm quality, offering a modifiable factor in fertility care.
When we talk about unexplained infertility, it accounts for about 30% of female infertility cases, which are diagnosed after ruling out tubal issues, ovulation defects, endometriosis, and uterine abnormalities via full investigations like laparoscopy. Normal ovulation is often seen in women and semen parameters, yet they fail to conceive after one year of regular unprotected intercourse. The biomarkers of Vitamin D, particularly calcitriol (the active form), distinguish the best in the patients who are away from fertile controls, with AUC values up to 0.909 for prediction.
Vitamin D plays a crucial role in reproductive health by supporting hormone balance, egg and sperm quality, and IVF outcomes in both men and women. Deficiency is common and linked to fertility issues like irregular ovulation, low sperm motility, and reduced pregnancy rates. Supplementation often improves these parameters, particularly in deficient individuals.
Vitamin D enhances follicular growth, AMH production, and egg quality, while deficiency correlates with PCOS severity and poor IVF success. Women with sufficient levels (>30 ng/mL) achieve higher clinical pregnancy rates post-IVF, with studies showing doubled conception chances. Supplementation boosts ovulation and pregnancy rates in PCOS patients, reducing androgen levels and miscarriage risk.
Vitamin D receptors on sperm improve motility, capacitation, and acrosome reaction, countering low count and poor morphology from deficiency. In oligoasthenozoospermic men, 6 months of supplementation significantly raises sperm concentration (from 19.7 to 33.6 million/mL) and progressive motility (from 22.9% to 35.2%). Fertile men typically have higher vitamin D levels than infertile men.
Unexplained infertility is diagnosed when standard testing (ovulation, tubal patency, semen analysis, and ovarian reserve) is normal. Because implantation problems and subtle oocyte/sperm quality issues aren’t always detected by routine tests, a deficiency that impairs endometrial receptivity or subtle gamete function could plausibly show up as “unexplained” infertility.
Several clinic studies specifically examining unexplained infertility have found lower 25(OH)D concentrations in affected women versus controls, and some small trials suggest targeted repletion improves intermediate outcomes (like endometrial markers or biochemical pregnancy). But evidence is not yet definitive for routine use purely to treat unexplained infertility — it’s a promising, plausible avenue that still needs stronger trial confirmation.
There is a strong biological rationale and growing clinical evidence linking vitamin D status with reproductive processes that matter for conception and implantation. Observational data and some intervention studies suggest deficiency is more common in subfertile populations—including those labelled “unexplained infertility” and correcting deficiency is reasonable and low risk. However, the evidence is not uniformly conclusive that routine high-dose vitamin D supplementation will improve live-birth rates for every infertile couple. For now, the most pragmatic approach is to test and correct vitamin D deficiency in people planning pregnancy or undergoing fertility treatment, while continuing to follow broader fertility-optimization strategies