Vitamin D and fertility

Vitamin D is a nutrient that acts as a hormone in our bodies. Therefore, vitamin D has multiple functions, from bone health and mineralization to modulation of reproductive processes in women and men (1, 2). This is very important, given the fact that about 50% of the population worldwide has Vitamin D deficiency, which is defined as serum concentrations of 25-hydroxyvitamin D levels of less than 20 ng/ml (1). Vitamin D deficiency is a risk factor for diabetes, obesity, osteomalacia, autoimmune diseases, cardiovascular diseases, dementia, and cancer (3).

Vitamin D can be consumed from foods rich in this vitamin, such as cod liver oil, egg yolk or fatty fish, vitamin D supplements, or fortified food. Our bodies can also produce vitamin D from ultraviolet-B (UV-B) in the skin (4), meaning that we can make vitamin D after exposure to sunlight. However, it is also well known that too much exposure to the sun can lead to skin cancer, so a lot of people are preferring to get vitamin D from other sources like foods or supplements.

The role of Vitamin D in fertility has been widely investigated. Actually, it has been found that in northern countries the pregnancy rates are higher during summer and autumn, and the lowest during winter and spring. There could be several explanations for this, and one of them is the lower levels of vitamin D metabolites in serum during winter and spring, which can affect several pathways like endometrial and oocyte development (2, 5). Vitamin D's active form, the 1,25(OH)2D3, stimulates the production of progesterone, estradiol, and estrone in human ovarian tissue (2).

Infertility is a multifactorial disorder that affects about 15% of couples, and it has big medical, psychosocial, and economic consequences (2). Polycystic ovary syndrome (PCOS) and endometriosis, major causes of female infertility, have been associated with vitamin D deficiency in some observational studies (1). The relation between vitamin D deficiency and PCOS might be related to the insulin resistance that characterizes some cases of PCOS since Vitamin D improves the action and response of insulin in the tissues (2). In the case of endometriosis, the association between this condition and vitamin D deficiency could be related to the immunomodulatory effect that vitamin D has. During endometriosis, there is a higher immune response and inflammation occurs, enabling the survival of endometrial implants (1). Vitamin D is also important for male fertility. Low levels of vitamin D are associated with low testosterone and poor semen quality, however, supplementation with vitamin D does not seem to improve these values (2), meaning that more studies are needed in this area to really identify what is the mechanism of action. Also, many authors found a positive relationship between vitamin D levels and sperm motility, total sperm count, and normal sperm morphology (3).

Regarding the supplementation with vitamin D in women or men with hormonal disturbances, there are still no specific guidelines. The Recommended Daily Allowance (RDA) of vitamin D should be 600 IU per day in individuals up to 70 years (2). Due to the frequency of vitamin D deficiency, it is advisable to talk to your doctor about this issue and have your doctor send the appropriate laboratory tests.

References

1.Voulgaris, N.; Papanastasiou, L.; Piaditis, G.; Angelousi, A.; Kaltsas, G.; Mastorakos, G. Kassi, E. Vitamin D and aspects of female fertility. Hormones 2017, 16(1):5-21. 2.Lerchbaum E, Obermayer-Pietsch B. Vitamin D and fertility: a systematic review. Eur J Endocrinol. 2012 May;166(5):765-78. doi: 10.1530/EJE-11-0984. Epub 2012 Jan 24. PMID: 22275473. 3.Cito G, Cocci A, Micelli E, Gabutti A, Russo GI, Coccia ME, Franco G, Serni S, Carini M, Natali A. Vitamin D and Male Fertility: An Updated Review. World J Mens Health. 2020 Apr;38(2):164-177. doi: 10.5534/wjmh.190057. Epub 2019 May 17. PMID: 31190482; PMCID: PMC7076312. 4.Pilz S, Zittermann A, Obeid R, Hahn A, Pludowski P, Trummer C, Lerchbaum E, Pérez-López FR, Karras SN, März W. The Role of Vitamin D in Fertility and during Pregnancy and Lactation: A Review of Clinical Data. Int J Environ Res Public Health. 2018 Oct 12;15(10):2241. doi: 10.3390/ijerph15102241. PMID: 30322097; PMCID: PMC6210343. 5. Muscogiuri G., Altieri B., de Angelis C., Palomba S., Pivonello R., Colao A., Orio F. Shedding new light on female fertility: The role of vitamin D. Rev. Endocr. Metab. Disord. 2017;18:273–283. doi: 10.1007/s11154-017-9407-2