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Vitamin D Deficiency and its Link to Fertility: What You Need to Know

drtanyawilliams - January 19, 2023 - 21 comments

It’s winter, which means our beloved sunshine, and therefore vitamin D, are hard to come by these days. Between fewer hours of sunlight and more time spent inside, most Canadians are in the same boat when it comes to vitamin D – it’s hard to get enough. That’s why, we’ve decided to talk about the link between vitamin D deficiency and fertility.

Back profile of a person with a dark winter coat and hat, sunlight peaking through the trees, in a wintery forest

Vitamin D and where we get it 

Vitamin D is a nutrient that helps us absorb and use calcium and phosphorous, which are both critical to bone health. 

Where do you get vitamin D? It’s only in a few foods, like fatty fish and egg yolks, and is fortified into some others. A major source is the sun, but how much vitamin D your body synthesizes is affected by several factors. These include season, time of day, clouds, smog, sunscreen, and your skin’s pigmentation.

Who is at risk of deficiency

The groups most likely to be deficient in vitamin D are older adults and those who have limited sun exposure, dark skin, conditions that limit fat absorption, obesity, or have undergone gastric bypass surgery.

Because Canada is at a higher latitude, it’s difficult for many Canadians to get enough vitamin D through sun exposure. According to Statistic Canada, in 2013, 68% of Canadians had more than a “sufficient” level of vitamin D (50 nmol/L), while 32% had less. In winter, 40% of Canadians were not getting sufficient amounts of the vitamin.

The problem with Vitamin D deficiency

Several recent studies have linked vitamin D deficiency to significantly higher morbidity and mortality. 

Being deficient in this vitamin creates problems with bone metabolism. This can cause rickets (skeleton deformations) in children, and osteomalacia (undermineralized bones) or osteoporosis (porous bones) in adults. 

On the other hand, having too much vitamin D creates hypercalcemia (too much calcium in the blood). This can calcify your kidneys and other soft tissues from heart, to lungs, to blood vessels.

Vitamin D and fertility

Vitamin D is known to be critical to musculoskeletal health. However, more research is suggesting its importance for fertility, pregnancy outcomes, and lactation. Some evidence suggests vitamin D not only modulates sex steroid hormones (typical regulators of human reproduction), but also female and male reproductive processes.

Observational studies found that being vitamin D-deficient increased the risk of lower fertility and unfavorable pregnancy outcomes, and was linked to low vitamin D in breast milk. 

A short-haired brunette woman with sunglasses holds her pregnant belly in a sunny field


If a woman is deficient in vitamin D, it could cause several problems in the reproductive system. One study found that vitamin D-deficient women had a much higher occurrence of uterine myomas. Amongst women with PCOS, low vitamin D links to obesity, as well as metabolic and endocrine disturbances. If you do have PCOS, supplementing vitamin D may improve the frequency of your periods and improve metabolic disturbances.

Getting enough of this vitamin may also have a number of positive effects on fertility. Because Vitamin D directly affects AMH production, women with a higher concentration of the vitamin are shown have been shown to maintain their ovarian reserve for longer. Getting enough vitamin D is also important for women undergoing IVF because of its benefits for the endometrium. Several observational studies found that women with sufficient vitamin D levels (≥30 ng/ml) had better IVF outcomes.

The research on this relationship is not yet robust enough to be conclusive, but taking the vitamin is still a common recommendation and appears to be safe. Supplementing vitamin D during pregnancy has been found to be safe and to improve vitamin D and calcium levels, which protects skeletal health. And because deficiency is so common, many pregnant women have to supplement to get a sufficient amount as per nutritional vitamin D guidelines. 


Researchers do not agreen on the relationship between vitamin D deficiency and male fertility. But most studies agree that vitamin D may positively affect men’s fertility potential by improving sperm motility. A 2013 review concluded that both low (<50 nmol/L) and high (>250 nmol/L) vitamin D levels negatively affect sperm count, movement, and morphology. When men have a normal vitamin D level, it also appears to link to better pregnancies.

Treating vitamin D deficiency

Male doctor in lab coat holds white pills in hands, indicating supplementation option to combat vitamin d deficiency and infertility that can be associated with it.

It’s a good idea to ask your doctor for a blood test to check your vitamin D levels. If you’re deficient, your doctor will probably suggest taking a D3 supplement. 

Public Health suggests that for people not getting enough sun, and who do not have contra-indications, supplementing 2000IU/day of D3 would likely get 93% of them to normal levels without risking toxicity.

As always, talk to your doctor to determine whether you should be supplementing, and how much.

Discover more related blogs from Dr. Tanya Williams Fertility Centre:

Fertility Supplements: Which Ones Actually Work?

7 Health Tips to Support Fertility

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