When you are planning or trying to get pregnant, a vitamin D level check should be part of your preparations. Although available research doesn’t allow us to conclude with certainty that vitamin D boosts fertility and conception rates, there is a growing interest in the potential role of vitamin D in human reproductive processes, both in women and men.
Vitamin D deficiency is also associated with a wide range of pregnancy complications. You have nothing to lose and possibly much to gain by optimizing your vitamin D levels as part of your preparations for a healthy pregnancy.
Research on vitamin D and fertility
While there is substantial evidence that vitamin D deficiency has negative effects on reproduction in animals, there is still relatively little research available that specifically look at the effects of vitamin D on human fertility.
A widely cited systematic review (an exhaustive summary of available research) by an Austrian research team, published in the European Journal of Endocrinology, made the following observations:
- The vitamin D receptor has been found in several human reproductive organs, including testes and sperm in men, and in the ovaries and placenta in women.
- Studies of the correlation between vitamin D levels and IVF outcomes had contradictory results, some showing better conception rates when vitamin D levels were higher and other studies failing to establish a similar relationship.
- Studies of the association between vitamin D levels and sperm motility also reported mixed results.
- Several studies found a correlation between low vitamin D and some, but not all of the symptoms of polycystic ovary syndrome (PCOS).
The researchers conclude:
We want to emphasize the fact that in infertility cases drastic improvements in reproductive failure may not be achieved by vitamin D treatment alone; however, vitamin D supplementation is a safe and cheap treatment, which might have some beneficial effects on human reproduction.
In a parallel systematic review, published in Reproductive Biology and Endocrinology, a German research team also reported contradictory results of human studies on the role of vitamin D in fertility and reproductive physiology. They conclude:
Human and animal data suggest that low vitamin D status is associated with impaired fertility, endometriosis and polycystic ovary syndrome. … However, confirmation of experimental observations establishing an association of vitamin D deficiency with adverse reproductive outcomes by high quality observational and large-scale randomized clinical trials is still lacking.
To summarize, it has not been clearly demonstrated that vitamin D has any significant effect on human fertility, but the evidence from animal studies and the hypothesis that a relationship may exist are still good reasons to optimize your vitamin D levels.
Other benefits of healthy vitamin D levels
It is well known that adequate levels of vitamin D support the absorption of calcium, which in turn ensures bone health and prevents osteoporosis. But an increasing number of medical studies also suggest a number of other health benefits, including the prevention of chronic diseases like diabetes, autoimmune diseases, cardiovascular disease and cancer.
Women with sufficient vitamin D levels are less likely to develop uterine fibroids (non-cancerous tumors in the uterus) than women who suffer from vitamin D deficiency.
Insufficient levels of vitamin D are also associated with a number of pregnancy complications, including gestational diabetes, pre-eclampsia, bacterial vaginosis and increased odds of primary cesarean section.
How much vitamin D do you need, and how do you get it?
Taking a blood test is the only way to find out if your vitamin D levels are sufficient. In the United States the test result will be given in ng/ml (nanograms per millilitre). In other countries, the result will often be expressed in nmol/l (nanomoles per litre).
Vitamin D levels above 30 ng/ml (75 nmol/l) are considered normal. Levels between 20 and 30 ng/ml (50-75 nmol/l) are considered an insufficiency, while 20 ng/ml (50 nmol/l) or less indicates a vitamin D deficiency.
As a minimum, therefore, you need to make sure that your vitamin D levels stay above 30 ng/ml (75 nmol/l). However, these official recommendations are based on the minimum amounts of nutrients needed to prevent deficiency diseases, not to ensure optimal health. The Vitamin D Council suggests that 50 ng/ml (125 nmol/l) is the ideal level to aim for.
So what can you do to achieve and maintain this ideal vitamin D level?
The most natural source of vitamin D is sunshine. The human body naturally generates vitamin D when the skin is exposed to the sun, and large amounts of vitamin D can be produced very rapidly this way.
It is not necessary to get burnt or even tanned to produce the amount of vitamin D you need; as little as 15 minutes per day may be enough for a very fair-skinned person. The more skin you expose, the more vitamin D your body will produce.
Because the amount of vitamin D you can get from sunshine depends on where you live, which time of the day you go outside, and on the color of your skin, it can be difficult to figure out how much time you need to spend in the sun.
As a rule of thumb, the Vitamin D Council recommends to expose your skin for half the time it takes for your skin to turn pink, and to expose as much skin as possible.
Getting enough vitamin D through your diet alone is almost impossible, and if you don’t get sufficient exposure to sunshine, you need to take a supplement. The best food sources of vitamin D include fat fish, egg yolks, beef liver, and fortified milk and cereals.
In many areas, there is simply not enough sunshine in the winter months to allow your body to produce sufficient vitamin D naturally. In addition, many of us spend most of our time indoors.
When sufficient sun exposure is not possible, taking a supplement is a simple and effective way to make sure you maintain a healthy vitamin D level. But how much supplement should you take?
In the last few years, there has been much controversy about vitamin D supplement recommendations. On one hand, a growing number of health professionals are complaining that official guidelines for vitamin D intake are much too low, as new medical research keeps demonstrating the potential health benefits of higher vitamin D levels.
On the other, skeptics are cautioning against the “vitamin D hype” in the absence of long-term clinical trials that reliably establish a relationship between cause and effect.
Here’s how the Vitamin D Council summarizes the recommendations from different organizations:
|Vitamin D Council||Endocrine Society||U.S. Food and
|Infants||1,000 IU/day||400-1,000 IU/day||400 IU/day|
per 25lbs of body weight
|600-1,000 IU/day||600 IU/day|
|Adults||5,000 IU/day||1,500-2,000 IU/day||600 IU/day,
800 IU/day for seniors
In another comprehensive review of Vitamin D recommendations, Dr Mark Hyman concludes that the average adult should take 2,000 IU of supplemental vitamin D a day. This can be a good baseline to start with, but some people may need significantly more to maintain vitamin D at healthy levels. Your best option is to talk to your doctor, and to regularly monitor your vitamin D levels to find the amount of supplement that works best for you.