What is the fertility vitamin D connection?
The gray winter months are here! As the days get shorter we see the sun less and less. And this equates to a higher chance of vitamin D deficiency in our fertility clients. So, what is the fertility vitamin D connection, and what can we do to help our clients get enough vitamin D in the darker months?
Vitamin D’s Role in Fertility
Vitamins and minerals have profound effects on our health throughout our lifetime. Vitamins act as gene “activators,” turning on and off switches for various tasks and processes in the body. Minerals are also involved in activating gene expression through their role as cofactors in the function of many enzymes.
Interestingly, the renal enzyme 1a-hydroxylase that activates 25OH-D to the active 1,25- dihydroxyvitamin D3 doesn’t just appear in the kidneys…it can also be found in the ovaries, breasts, and prostate. The receptor for vitamin D, helpfully called “vitamin D receptor,” or VDR for short, is a nuclear hormone receptor. This means that VDR is found in the cytoplasm (the shape-giving “goo” inside a cell in which all the organelles reside) until vitamin D enters the cell. Once vitamin D is bound to VDR, the vitamin D/receptor complex heads straight to the nucleus to interact with specific DNA sequences, described above. VDR is also found in the ovaries, uterus, placenta, and testes, as well as the hypothalamus and pituitary. Our reproductive organs are definitely interacting with vitamin D (1)! But what are the particulars of those interactions?
Some pattern have emerged around the vitamin D fertility connection—a sufficient amount of vitamin D does seem linked to more robust fertility in both men and women. In Northern countries, with less direct sunlight in the winter months, pregnancy rates peak in the vitamin D-rich months of summer and autumn (2). In a group of 132 women, pregnancy rates were higher for women who ingested the Estimated Average Requirement of daily vitamin D (10 μg/d) and were vitamin D sufficient (≥ 50 nmol/L) compared to women who were not (3). Studies of women participating in assisted reproductive treatments also confirm this:
“Compared to women with deficient or insufficient vitamin D status, women with replete vitamin D status had more live births (odds ratio (OR): 1.33; 95% confidence interval (CI): 1.08 to 1.65), more positive pregnancy tests (OR: 1.34; 95% CI: 1.04 to 1.73) and more clinical pregnancies (OR: 1.46; 95% CI: 1.05 to 2.02), whereas there was no association between miscarriage and vitamin D status. (4)”
In men, vitamin D was significantly higher in fertile study participants compared to infertile ones. A connection between vitamin D and sperm motility was also found (5).
However, as stated above, this is a pattern, not a rule. A 2021 systematic review and meta-analysis found no significant associations between vitamin D and markers of ovarian reserve—anti-Mullerian hormone (AMH), antral follicle count (AFC), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and LH/FSH ratio (6). And while observational studies have generally found connections between infertility and vitamin D deficiency, evidence from randomized controlled trials is not so less clear.
The “Why” Behind the Fertility Vitamin D Connection
So, why might vitamin D positively affect fertility? One mechanism is the connection between vitamin D and anti-Mullerian hormone. Sufficient vitamin D may have a positive influence on the production of AMH, thus increasing ovarian reserve. Vitamin D may also play a role in the successful implantation of the embryo and beneficial maternal/fetal immune balance (7, 8).
Practical Vitamin D Solutions
Ultimately, our levels of vitamin D and our response to intake, either through food or supplements, are highly variable due to our diet, lifestyle, use of pharmaceutical drugs, and genetic variations. So, intake and testing are important! I often suggest that my fertility clients check their levels twice per year, using either summer/winter solstice or fall/spring time changes as testing landmarks.
And let’s not forget about good food! The foods below are rich sources of vitamin D:
- Cod liver oil
- Seafood, specifically trout
- Organ meats, particularly liver and kidney, from pasture-raised animals
- Lard from pasture-raised pigs
- Pasture-raised chicken, duck, and goose with the skin
- Dairy fat from pasture-raised animals
- Egg yolks from pasture-raised eggs
Vitamin D3 occurs in animal foods and can be synthesized from sunshine or even UVB sun lamps with the help of the cholesterol in our skin. If your client is committed to a vegan diet, look for vegan supplements that list D as D3 (cholecalciferol) rather than D2.