When you are preparing your body for the baby you hope to welcome, AMH is often one of the first numbers you are given — and one of the least explained. It’s commonly described as a measure of egg reserve, yet AMH is more accurately a signal produced by developing follicles, reflecting how the ovary is regulating early follicle growth. Long before ovulation or implantation are in view, follicles are maturing quietly in the background, guided by a complex signalling environment that depends on adequate nutritional supply. Vitamin D plays a role within this early phase of fertility physiology, supporting the conditions in which follicles communicate, respond, and progress appropriately. In this way, Vitamin D is relevant early in your fertility cycle, linking nourishment today with the follicle development that will shape fertility months from now.
What Is Vitamin D?
Vitamin D is a fat-soluble nutrient that influences how cells signal, respond, and coordinate activity across many tissues, including the ovary, uterus, testes, and placenta. It is considered essential, as the body cannot reliably make enough without regular exposure to sunlight or dietary sources. Vitamin D plays a role in how minerals are used in the body, how immune responses are regulated, and how tissues grow and renew. Because it is fat-soluble, it is absorbed with dietary fat and stored in body tissues, where it can be drawn on to support ongoing physiological needs.
How Much Vitamin D Does the Body Require?
The European Food Safety Authority (EFSA) provides dietary reference values for Vitamin D for the general population.
For adults, EFSA sets an Adequate Intake (AI) of 15 µg (600 IU) per day to support normal physiological function and help prevent deficiency.
These EFSA values are conventional public-health reference intakes. In functional medicine, Vitamin D requirements are often considered closer to the tolerable upper intake level (TUL), reflecting a focus on functional sufficiency rather than minimum adequacy.
The Role of Vitamin D in Fertility and Pregnancy
Vitamin D is active early in fertility physiology, long before ovulation or implantation occur. During the earliest stages of follicle development, it supports the signalling environment within the ovary, influencing how developing follicles communicate and respond to hormonal cues. This includes a role in AMH regulation, helping guide how follicles progress through early growth rather than accelerating or stalling development. In this way, Vitamin D contributes to the conditions that shape egg development months before a cycle begins.
Vitamin D and AMH become more relevant in IVF because stimulation places greater demand on early follicle signalling, which directly affects how many follicles grow in sync, how many eggs reach full maturity, and how many mature eggs are ultimately collected at retrieval.
As fertility moves closer to conception, Vitamin D continues to play a role in preparing the body for implantation. It supports endometrial receptivity, helping the uterine lining respond appropriately to embryonic signals, and contributes to immune balance at the implantation site. This balanced immune response allows implantation to occur while maintaining appropriate tissue remodelling and tolerance.
Vitamin D remains relevant as pregnancy establishes and progresses. It supports placental development, vascular function, and immune coordination within the maternal–placental interface. Adequate Vitamin D availability during pregnancy has been associated with a reduced risk of pre-eclampsia, reflecting its role in supporting healthy placental signalling and blood vessel regulation.
Across fertility and pregnancy, Vitamin D functions as a signalling nutrient, supporting coordination between ovarian activity, uterine readiness, and placental development from early follicle growth through to later stages of gestation.
Vitamin D and Male Fertility
Vitamin D also plays a role in male fertility, supporting sperm development and function through cellular signalling within reproductive tissues. During spermatogenesis, sperm cells undergo continuous division, maturation, and structural change, processes that depend on a stable internal environment rather than short-term interventions.
Vitamin D supports how sperm cells develop and respond to hormonal and local signals within the testes. Adequate availability is associated with healthier sperm characteristics, including motility and structural integrity, reflecting its role in supporting normal sperm maturation rather than stimulating production.
Vitamin D is involved in signalling related to testosterone production and testosterone responsiveness, both of which influence sperm production, maturation, and motility. By supporting this hormonal environment, Vitamin D contributes to the conditions needed for consistent sperm development over time.
In this way, Vitamin D contributes to male fertility during the months when sperm are being formed and matured, shaping the quality of sperm available at the time of conception.
Vitamin D and Sperm–Egg Interaction
For fertilisation to occur, sperm must do more than reach the egg. They must undergo a final set of changes that allow them to bind to and penetrate the egg’s outer layers.
Vitamin D supports this stage by contributing to calcium signalling within sperm cells. This signalling is required for sperm activation and hyperactivated movement, for the acrosome reaction—the controlled release of enzymes that allow sperm to penetrate the egg—and for the final interaction between sperm and egg at fertilisation.
When this signalling environment is supported, sperm are better able to complete the final steps required for fertilisation, rather than stopping at movement alone.
Food Sources of Vitamin D
Vitamin D is present in a relatively small number of foods, making consistent dietary intake more dependent on food quality and selection than on volume alone. Natural food sources of Vitamin D are primarily found in animal-based foods, where it appears in forms the body can readily use.
Oily fish such as salmon, sardines, mackerel, and trout are among the richest dietary sources of Vitamin D and feature regularly in fertility-supportive meal patterns. Egg yolks also provide Vitamin D, linking this nutrient directly to egg quality and early developmental nourishment. Liver and liver-based foods contain Vitamin D alongside other fat-soluble nutrients involved in reproductive signalling.
Some foods, including dairy products and plant-based alternatives, may contain added Vitamin D through fortification. While these can contribute to overall intake, naturally occurring sources provide Vitamin D within a broader nutritional context that supports absorption and utilisation.
Because Vitamin D is fat-soluble, it is best absorbed when consumed as part of a meal that contains dietary fat. This reinforces the role of whole foods and balanced meals in supporting Vitamin D availability through everyday nourishment.
Synergists and Antagonists
Vitamin D does not act in isolation. Its role in fertility physiology depends on the presence and balance of other nutrients that support absorption, signalling, and downstream function.
Synergists
Calcium
Vitamin D supports how calcium is absorbed and directed within the body. Calcium appears alongside Vitamin D in early developmental and pregnancy-related physiology, reflecting their shared role in cellular attachment, structural signalling, and placental function.
Magnesium
Magnesium supports the body’s ability to utilise Vitamin D effectively. Where magnesium supply is limited, Vitamin D activity may be reduced, even when intake appears adequate.
Vitamin K
Vitamin K works alongside Vitamin D in calcium handling, helping ensure that calcium is directed into appropriate tissues. This supports Vitamin D’s signalling role rather than acting as a standalone nutrient.
Zinc
Zinc supports cell division, hormone signalling, and early embryonic processes. It appears repeatedly in fertility physiology alongside Vitamin D, particularly in relation to implantation and early development.
Antagonists
Excess Vitamin A (retinol)
High intakes of retinol can interfere with the balance of fat-soluble nutrients, reducing the effectiveness of Vitamin D signalling within reproductive tissues.
Imbalance among fat-soluble nutrients
Vitamin D functions as part of a wider fat-soluble nutrient system. When intake is consistently skewed toward one nutrient over others, coordinated signalling may be disrupted.
Bringing Vitamin D Into Everyday Nourishment
Because Vitamin D is present in relatively few foods, everyday nourishment works best when intake is consistent rather than occasional. Meals that include oily fish or eggs naturally bring Vitamin D into the diet while also supplying fat, which supports absorption.
A simple example is a meal built around eggs, where the yolk provides Vitamin D alongside other nutrients involved in early fertility signalling. Pairing eggs with vegetables cooked in olive oil or butter supports both nutrient intake and utilisation, reinforcing how Vitamin D fits into ordinary meals rather than standing apart from them.
Sunlight Is the Primary Source
Unlike most nutrients involved in fertility, Vitamin D is produced primarily in the skin through sunlight exposure.. The main source of Vitamin D is sunlight, produced in the skin in response to ultraviolet B (UVB) exposure.
Dietary sources of Vitamin D are relatively limited and tend to provide smaller, more variable amounts. For this reason, food alone often plays a supporting role rather than acting as the primary foundation of Vitamin D availability.
Season, latitude, time spent outdoors, and skin exposure all influence how much Vitamin D the body can produce. Where sunlight exposure is reduced or inconsistent, additional sources of Vitamin D may be needed to support ongoing physiological demand.
Why Nutrients Are Considered Together
Even though sunlight is the main source of Vitamin D, its role in the body depends on the presence of other nutrients. Vitamin D functions within a wider network that includes calcium, magnesium, vitamin K, and zinc, which support how it is directed and used within the body.
For this reason, Vitamin D is best understood as part of a coordinated nutrient system rather than as a standalone input. Consistent availability of these supporting nutrients helps maintain effective signalling across fertility, implantation, and pregnancy physiology.
Because Vitamin D is not primarily food-derived, diet alone often does not provide a complete supply. Natural food sources of Vitamin D are limited, and intake can vary widely depending on dietary pattern, seasonal availability, and individual absorption.
Many multivitamins include small amounts of Vitamin D, which may contribute to overall intake but are not always sufficient to support ongoing physiological demand. For this reason, Vitamin D is often considered separately from broad multinutrient formulas.
At Now Baby, we prefer a Vitamin D spray supplement that is paired with Vitamin K. This format supports absorption and reflects how Vitamin D functions alongside other fat-soluble nutrients rather than in isolation. Used in this way, supplementation acts as a scaffold alongside nourishment, supporting consistent availability without replacing it.
At Now Baby, we support fertility through physiology-led nourishment, translating complex biology into everyday food.
You can read about other essential nutrients for fertility here;
