If you’ve never considered how important vitamin D is for your fertility and during pregnancy, you might be shocked by how much this “sunshine vitamin” affects far more than just your skin tone. From bone health to blood sugar stabilization, and blood pressure management to mood, vitamin D is crucial for every woman, especially those trying to conceive.
But what levels are optimal for functional fertility? Should every woman take a supplement, regardless of her health status and geographic location? What happens when levels are sub-optimal? Let’s discuss that and more below.
Understanding Vitamin D
Vitamin D got its nickname, “the sunshine vitamin,” because it’s the only nutrient our bodies derive from the sun. Like Vitamins A, E, and K, Vitamin D is characterized as a fat-soluble vitamin, meaning that it “can dissolve in fats and oils,” according to the Национальный институт рака. The most common form of Vitamin D (there are actually six different kinds!) is synthesized from cholesterol [1]. Vitamin D is primarily stored in the liver, with small amounts stored in fatty tissue throughout the body.
You’re perhaps aware that Vitamin D is vital for proper absorption of calcium and phosphorus in the body (this is partly why milk, which is naturally high in calcium, is often fortified with Vitamin D). Additionally, Vitamin D is also a steroid hormone that plays a key role in reproductive health [2].
How the body uses Vitamin D
When your skin is exposed to the sun, the cholesterol in your skin absorbs Vitamin D and converts it into usable forms. From there, Vitamin D:
- Helps your bones absorb calcium and phosphorus through the gastrointestinal tract, and influences bone formation and mineralization (this is Vitamin D’s main role in the body);
- Plays a key role in regulating the creation of inflammatory compounds;
- Has receptor sites on muscle cells that affect muscle formation by influencing the mitochondria;
- Influences insulin, and may in turn influence blood sugar balance [3].
This is just scratching the surface of how Vitamin D works throughout your body. Let’s take a closer look at what it means specifically for fertility and pregnancy.
Vitamin D and female fertility
Vitamin D has receptor sites throughout the body, including on or within the reproductive organs, tissues, and cells in both men and women [4]. Vitamin D receptors communicate with the hypothalamus in the brain, which in turn regulates production of progesterone, estradiol, and estrone. (For reference, estradiol is the primary form of estrogen secreted during the fertile years, whereas estrone is secreted after менопауза.) Vitamin D levels also influence follicle-stimulating hormone (FSH) production and the maturation of individual follicles [5].
During the menstrual cycle, Vitamin D plays a significant role in фолликулярная фаза, as estrogen levels rise and a follicle matures in preparation for ovulation. Then, after ovulation, Vitamin D is needed to sustain a healthy corpus luteum, which is responsible for progesterone production in the luteal phase of the menstrual cycle, plus early on in a pregnancy [6].
During the menstrual cycle, Vitamin D plays a significant role in the follicular phase, as estrogen levels rise and a follicle matures in preparation for ovulation. Then, after ovulation, Vitamin D is needed to sustain a healthy corpus luteum, which is responsible for progesterone production in the luteal phase of the menstrual cycle, plus early on in a pregnancy.
You can see from the above that Vitamin D is clearly integral to female hormone production, and without it, how female fertility might suffer! In fact, low Vitamin D is linked to:
- Oligomenorrhoea (long cycles and infrequent periods)
- Amenorrhea (absent periods)
- Polycystic Ovary Syndrome (PCOS) [4]
- Low Anti-Müllerian hormone (AMH) (low AMH levels may influence rates of conception)
- Эндометриоз
Simply raising Vitamin D levels won’t necessarily correct infertility or other health issues
Despite Vitamin D’s importance to the female reproductive system, исследование yields conflicting results on whether simply supplementing Vitamin D will improve fertility outcomes [4]. When you’re healthy and have no underlying conditions, taking more Vitamin D май improve your fertility. But if you have an underlying health condition like PCOS or endometriosis, supplementing Vitamin D alone may not be enough to overcome infertility.
Vitamin D and male fertility
We also can’t forget that men are necessary for making a baby, and Vitamin D dramatically affects men’s fertility, too. Vitamin D is crucial for spermatogenesis (the process of creating sperm) and is believed to influence sperm motility and function [7]. Additionally, more Vitamin D is associated with higher testosterone levels [8].
However, similar to female fertility, evidence suggests a positive relationship between the Vitamin D levels and testosterone in already-healthy men [4]. In contrast, for men with underlying health conditions, supplementation with Vitamin D alone may not meaningfully impact testosterone levels. This suggests that getting to the root cause of infertility is more complex than simply increasing one’s serum (the amount circulating in the blood) Vitamin D levels.
Vitamin D and pregnancy
Once your baby is conceived, Vitamin D plays a role in “decidualization, implantation, expression of human placental lactogen (hPL), secretion of human chorionic gonadotropin (hCG), progesterone and estrogen levels, calcium-uptake in the placenta and the immune responses of the placenta” [4].
As your baby develops, Vitamin D is also crucial for the growth and development of his or her bones, organs, and tissues. And if your Vitamin D intake isn’t sufficient, your body will actually pull from your Vitamin D stores to supply your baby’s needs.
Without sufficient Vitamin D, your and your baby’s health are at risk
Ongoing research is likewise exploring the possibility of a link between Vitamin D and miscarriage rates [2][9]. Low Vitamin D is also connected to pregnancy complications for the mother and baby. For the mother, low Vitamin D levels are specifically associated with higher incidence of high blood pressure (gestational hypertension), gestational diabetes, preeclampsia, preterm birth, and postpartum mood disorders [4]. For the baby, low Vitamin D levels are associated with low birth weight, low calcium levels, poor post-birth growth, fragile bones, and an increased risk of developing autoimmune disorders in the future [10].
Normal levels of Vitamin D and RDA during pregnancy
But what is a normal level of Vitamin D, anyway? In the United States, the standard Vitamin D level is 20 ng/mL to 60 ng/mL, with optimal levels ranging from 40 ng/mL to 70 ng/mL. And the standard recommended daily allowance (RDA) per person is 600 IU/day. I differentiate standard vs. optimal because there is lack of clarity in the research literature on what is optimal for fertile and pregnant women vs. what is acceptable for the general population.
Lily Nichols, RDN, writes, “The Institute of Medicine sets the RDA for vitamin D at 600 IU/day; however, several studies have found this level of intake to be insufficient to maintain normal vitamin D levels throughout pregnancy.“ (See Real Food For Pregnancy, Ch 6).
As with any lab value, your physiology will determine how much vitamin D you need for thriving fertility and potential pregnancy. Therefore, consider the specific lab values with caution and investigate further for your particular situation.
Signs of Vitamin D deficiency
Strikingly, it’s believed that nearly 40% of the population is Vitamin D deficient. If you don’t get enough exposure to sunlight, don’t eat foods high in Vitamin D, have kidney problems, or have trouble with digestive tract absorption (as is the case with celiac disease, bariatric surgery, or inflammatory bowel disease), your Vitamin D levels may be low. Though it’s difficult to pin down an “ideal” Vitamin D level because we all have different needs, there are still recognizable signs of deficiency.
Common signs of vitamin D deficiency include:
- Ановуляция
- Oligomenorrhea
- Amenorrhea
- Усталость
- Muscle weakness
- Bone pain
- Mood changes, like depression or anxiety
Of course, these symptoms could be caused and/or exacerbated by a variety of health conditions. That’s why low Vitamin D is rarely a stand-alone issue. As mentioned above, simply supplementing with Vitamin D без improving overall health may increase serum Vitamin D levels, but may not affect fertility rates.
Sources of Vitamin D
Start with the sun
The sun is a free and simple source to meet most of your Vitamin D RDA. In fact, 90% of our Vitamin D levels come from the sun [11]. Aim for getting out in the sun midday, between 10 am and 4 pm. Although the time required will vary depending on each person, 5-30 minutes should be sufficient. Then, if you feel the need to put on sunscreen or protective clothing, you can rest assured that you’ve gotten your Vitamin D for the day.
Of course, the season of the year, region, cloud cover, fog, length of day, amount of melanin in your skin, and sunscreen can all affect just how much Vitamin D you get from the sun. If you’re unable to soak up some rays for 5-30 minutes per day at least a few times per week, it may be wise to focus next on food and supplements.
Eat foods high in Vitamin D
The best food sources of Vitamin D are found in oily fish; think cod liver oil, trout, and salmon. But you can also find a decent amount in mushrooms, fortified milks, and egg yolks. As with all food, it’s important to source the best food you can afford. Although processed foods may contain higher levels of fortified Vitamin D, there are several other concerns with processed foods that you may want to consider for your overall health.
Consider supplements
If the sun is hard to come by and you can’t get your hands on fresh fish, supplements may be your next best bet. When sourced well, добавки can help fill the gaps in your Vitamin D intake. Vitamin D2 supplements are derived from mushrooms or yeast, whereas Vitamin D3 supplements are derived from animal products. Although both are metabolized and function similarly, there is some доказательства suggesting that Vitamin D3 increases serum levels to a greater extent and maintains them more effectively than D2.
Lily Nichols, RDN, recommends consulting with your healthcare team to determine your specific Vitamin D level before starting a supplement. That way, you can periodically check your numbers to see if the supplements are right for your specific needs.
As mentioned previously, Nichols believes that current RDA limits are too low for pregnant and nursing mothers and recommends starting with 4000 IU per day, which is more than six times the RDA. (See Real Food for Pregnancy, Chapter 6) This is the case for most prenatal vitamins, they may have vitamin D included but the IU is not optimal.
Finally, to optimize vitamin D supplement (or food source) absorption, consider taking it with magnesium, followed by a healthy fat source such as avocado or nuts.
Can you take too much vitamin D?
It’s important to note that though toxicity is rare, it можно occur with high doses of Vitamin D. Vitamin D is a fat-soluble vitamin, which means it isn’t excreted in the urine like water-soluble vitamins. Excess Vitamin D is stored in your fat cells, where it then increases calcium absorption (this is called hypercalcemia).
The National Institutes of Health states, “Hypercalcemia, in turn, can lead to nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones.” For this reason, it’s important to have your Vitamin D levels checked before supplementing beyond whatever is in your multivitamin or prenatal vitamin.
The bottom line for vitamin D for fertility and pregnancy
As you can see, Vitamin D is an essential vitamin for both men and women. Without this “sunshine vitamin,” many physiological processes suffer, including menstrual health and pregnancy outcomes. If you suspect you have a Vitamin D deficiency, work with your healthcare team to identify the root cause of your deficiency, giving yourself the best chance at improving your overall health and achieving your health goals.
