Vitamin D Deficiency in Women: Symptoms & What Helps

This article is part of: Micronutrients and Hormones: The Female Guide

Brief definition

A vitamin D deficiency in women is defined as a 25-OH vitamin D level in the blood that is too low – according to the German Nutrition Society (DGE), below 30 nmol/l (12 ng/ml). Vitamin D acts more like a hormone than a classic vitamin and is involved in bone, muscle, and immune system health. Since we mainly produce it in our skin through sunlight, a deficiency is widespread, especially in the winter months.

The most important facts at a glance

Vitamin D deficiency is very common in women in Germany, especially during the winter half-year.
Typical symptoms can include fatigue, muscle weakness, bone pain, and increased susceptibility to infection.
Risk groups include pregnant women, women with PCOS or Hashimoto's, those in perimenopause, as well as those with darker skin types or limited sun exposure.
The evidence is particularly strong for bones, muscles, and the immune system – provided there is an actual deficiency.
A deficiency is defined as a level below 30 nmol/l (12 ng/ml); levels above 50 nmol/l (20 ng/ml) are considered sufficient.
The principle is: first test, then dose – and do not permanently exceed the safe upper limit (EFSA: 4000 IU/day).

In my consultations, I hear one sentence particularly often: "I'm constantly tired, something isn't right." And yes, sometimes a vitamin D deficiency is indeed behind it. Vitamin D is a valuable building block that many women in Germany carry around with insufficient levels for large parts of the year.

In this article, I want to show you how to recognize a deficiency, what the studies truly reveal (and what they don't), and how you can approach it pragmatically in your daily life. Without scaremongering, without promises of miracles, but honestly and structured, just as I would explain it to a friend.

How do I recognize a vitamin D deficiency as a woman?

The honest answer: often not reliably from the symptoms alone. A vitamin D deficiency can manifest as persistent fatigue, muscle weakness, muscle or bone pain, and increased susceptibility to infection. The problem: These symptoms are very non-specific and can have many other causes, from iron deficiency to thyroid issues to sleep deprivation. Therefore, a deficiency can ultimately only be truly determined through a blood test (25-OH vitamin D). The following overview shows where the research is clearest.

Area	What studies show
Bones & Muscles	In case of a deficiency, the risk of muscle weakness, falls, and bone problems increases; correcting the deficiency can help here.
Immune System	A large meta-analysis (Martineau 2017) suggests that supplementation can reduce respiratory infections – especially with previously low levels.
Mood	The data is mixed; a clear, reliable effect on mood cannot be consistently proven.
Risk Groups	Pregnant women, women with PCOS or Hashimoto's, darker skin types, and people with little sun exposure are more frequently undersupplied.
Reference Value	According to the DGE, a deficiency exists below 30 nmol/l (12 ng/ml); levels from 50 nmol/l (20 ng/ml) are considered sufficient.

Did you know?

According to data from the nationwide DEGS1 study by the Robert Koch Institute (RKI), a large proportion of adults in Germany do not reach the recommended vitamin D level – around 30% are in the deficiency range, and over half do not achieve optimal supply, with significant fluctuations between summer and winter.

What a vitamin D deficiency means for women

A vitamin D deficiency rarely manifests with a single, clear symptom. More often, it is a diffuse overall picture: persistent fatigue and exhaustion, muscle weakness or a heavy feeling in the legs, muscle and bone pain, and increased susceptibility to infections. Some women also report a depressed mood. It remains important: these symptoms are non-specific and do not, in themselves, prove a deficiency – they are more of a reason to take a closer look.

Some women are at a higher risk. These include pregnant women (the need increases and the child's supply is also dependent on it), women with PCOS, where a deficiency occurs more frequently, and women with Hashimoto's or other autoimmune conditions. Perimenopause also deserves attention, as hormone levels are already in flux and bone health becomes more important. In addition, there are physical and lifestyle factors: darker skin types produce less vitamin D with the same sun exposure, and those who spend a lot of time indoors, consistently apply sunscreen, or – like almost everyone in Germany and Austria – experience a long winter with low-lying sun, will hardly get sufficient amounts through their skin.

What the studies really show

The most robust evidence concerns bones and muscles. Studies have shown that a pronounced deficiency is associated with muscle weakness, a higher risk of falls, and bone problems – and that it makes sense to compensate for such a deficiency. There is also good evidence for the immune system: a large meta-analysis of individual patient data (Martineau 2017) suggests that supplementation can reduce acute respiratory infections, with the benefit primarily occurring in women with previously low levels.

The picture is more mixed for mood and metabolism. For mood, the data do not show a clear, reliable effect – some studies suggest a small benefit, others find none. For PCOS and insulin resistance, a meta-analysis (Łagowska 2018) suggested possible beneficial effects, but the studies are heterogeneous and do not yet allow for a strong recommendation.

And then there is the honest flip side, which is often overlooked: those who are already very well supplied (which, objectively speaking, is not common) hardly benefit from additional vitamin D. Large studies such as VITAL (LeBoff 2022) showed that supplementation did not reduce the number of bone fractures in people without a deficiency.

Hormonic Base: Vitamin D3 plus 15 Micronutrients

Hormonic Base provides vitamin D3 along with 15 other micronutrients for your daily basic supply. Vitamin D contributes to the normal function of the immune system and the maintenance of normal bones.

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Reference Values, Testing, and Correct Dosage

A deficiency is indicated by the 25-OH-Vitamin D level in the blood. As a general guideline according to the DGE:

Deficiency: below 30 nmol/l (below 12 ng/ml)
Suboptimal: 30 to below 50 nmol/l (12 to below 20 ng/ml)
Sufficient: 50 nmol/l and above (20 ng/ml and above)
DGE reference value without endogenous production through sun exposure: 800 IU (20 µg) per day
Safe upper limit for continuous intake (EFSA): 4000 IU (100 µg) per day

My most important advice as a doctor: first test, then dose. A blood test involves little effort and saves you from guessing. I advise against high-dose courses based on suspicion – not out of overcautiousness, but because too much vitamin D over a long period can be harmful. Chronically high overdosing can lead to hypercalcemia, a dangerously elevated calcium level. A genuine high-dose therapy for a confirmed severe deficiency should therefore always be under medical supervision.

How Hormonic can help

For daily basic supply, we have developed Hormonic Base– a combination of 16 micronutrients, which also includes Vitamin D3. According to approved EFSA statements: Vitamin D contributes to the normal function of the immune system and the maintenance of normal bones. The base is supplemented by magnesium, zinc, and selenium, among others, which together form a solid foundation for daily life.

The principle remains important: test first. Via our Hormone Diagnostics Kityou can have your status determined before supplementing specifically. And if you are unsure how to interpret your values, you can speak to one of our doctors in a free 15-minute consultation.

Honestly: Hormonic Base is a daily basic supply – and not a substitute for targeted medical high-dose therapy if a severe deficiency is confirmed. That's exactly what the path of testing and medical supervision is for.

Not sure if you have a deficiency?

Test it together with the important hormone and blood markers conveniently from home with the Hormonic Diagnostic Kit. Medically supervised, for more clarity instead of puzzles.

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Conclusion

Vitamin D deficiency is common among women in Germany, especially in winter, and it can manifest itself in non-specific symptoms such as fatigue, muscle weakness or increased susceptibility to infection. The evidence is strongest for bones, muscles and the immune system – but especially when there is actually a deficiency. Those who are already well supplied gain little from more vitamin D. The most sensible approach is therefore neither to ignore it nor to blindly take high doses, but to test, evaluate the level and, if necessary, supplement moderately – always under medical supervision in the case of severe deficiency. Our doctors at Hormonic are always there to support you. Hereyou can book a free consultation to get all your questions answered via video call.

Common Questions About Vitamin D Deficiency in Women

What are the symptoms of vitamin D deficiency in women?

Typical signs can include persistent fatigue, muscle weakness, muscle and bone pain, and increased susceptibility to infection; some women also report low mood. However, these symptoms are non-specific and can have many causes – only a blood test (25-OH-Vitamin D) can provide certainty.

How much vitamin D per day for women?

The DGE recommends 800 IU (20 µg) per day as a reference value if the body does not produce enough vitamin D through sunlight. According to EFSA, the safe upper limit for long-term intake is 4000 IU per day. The most sensible approach is to base the dosage on measured blood levels: first test, then dose.

Ab wann spricht man von einem Vitamin-D-Mangel?

Von einem Vitamin-D-Mangel spricht man nach Definition der DGE, wenn der 25-OH-Vitamin-D-Spiegel im Blut unter 30 nmol/l (unter 12 ng/ml) liegt. Werte zwischen 30 und 50 nmol/l (12 bis 20 ng/ml) gelten als suboptimal, ab 50 nmol/l (20 ng/ml) gilt die Versorgung als ausreichend.

Kann man Vitamin D überdosieren?

Ja. Vitamin D wird im Körper gespeichert, deshalb kann eine dauerhaft zu hohe Zufuhr schaden. Bei starker Überdosierung über lange Zeit kann eine Hyperkalzämie entstehen, also ein gefährlich erhöhter Kalziumspiegel. Die EFSA nennt 4000 IE pro Tag als sichere Obergrenze; hochdosierte Kuren gehören in ärztliche Hand.

Scientific Sources

Rabenberg, M. et al. (2015). Vitamin D status among adults in Germany (DEGS1). BMC Public Health, 15, 641. doi:10.1186/s12889-015-2016-7
Martineau, A. R. et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: individual participant data meta-analysis. BMJ, 356, i6583. doi:10.1136/bmj.i6583
LeBoff, M. S. et al. (2022). Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults (VITAL). New England Journal of Medicine, 387, 299-309. doi:10.1056/NEJMoa2202106
Łagowska, K. et al. (2018). The Role of Vitamin D Oral Supplementation in Insulin Resistance in Women with PCOS: a meta-analysis of RCTs. Nutrients, 10(11), 1637. doi:10.3390/nu10111637
Mikola, T. et al. (2023). The effect of vitamin D supplementation on depression: dose-response meta-analysis of RCTs. Psychological Medicine, 53(16), 7509-7520. doi:10.1017/S0033291723002333
Palacios, C. et al. (2024). Vitamin D supplementation for women during pregnancy. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.CD008873.pub5

About the Author

Lisa Maria Emmer

Founder · Physician · Hormonic

Lisa Maria Emmer is a doctor and co-founder of Hormonic. She translates current studies and guidelines into understandable, honest recommendations for women – without promising miraculous cures, but with the aim of making health practical and scientifically sound for everyday life.

Note: This article is based on current guidelines and scientific work (as of 2026). It is for informational purposes only and does not replace professional medical advice, diagnosis, or treatment.