Tired. But not the kind of tired that a free weekend fixes. Add muscles that feel heavier than they used to, one infection too many over winter, and a mood that flattens noticeably from January onwards. Vitamin D rarely comes up first, because not one of those signs is specific on its own. That is exactly what makes vitamin D deficiency in women so common and so easy to miss.
In short: how do you recognise vitamin D deficiency?
- The typical pattern is persistent fatigue, muscle weakness and muscle aches, more frequent infections, low mood and dull bone pain
- All of it is non-specific. Only the blood test 25-hydroxyvitamin D gives you clarity
- Below 12 ng/mL (30 nmol/L) is deficiency. Above that, guidelines disagree on where sufficiency starts
- Around six in ten adults in Germany fall below 50 nmol/L, considerably more through the winter half of the year
- Once a deficiency is corrected, a maintenance dose of 1,000 to 2,000 IU daily is commonly described for adults
A low level can be raised reliably. It takes weeks to months, not days.
Topics in this article
Vitamin D is not really a vitamin. It is a hormone precursor, and the body makes most of it itself, in the skin, under UV-B light. Food contributes only a small share. That single peculiarity explains almost all of the confusion that has built up around the topic.
Because in Central Europe a low level is not an exception and not a personal failing. It is the norm, at least for a good part of the year. For where vitamin D sits in the bigger picture, see my overview of the blood tests women over 40 should consider.
Why vitamin D is so often low in women
From October to March the sun sits too low in Central Europe. The UV-B radiation needed for synthesis in the skin barely reaches the ground during those months. You can walk for two hours in February and still make no vitamin D at all. Through winter the body lives off what it stored over summer.
What that looks like in numbers comes from the largest German health survey to date. In the DEGS1 survey by the Robert Koch Institute, covering nearly 7,000 adults, 61.6 percent were below 50 nmol/L and 30.2 percent below 30 nmol/L. There was no meaningful difference between women and men. The seasonal difference was pronounced: in summer roughly half reached the target level, while through the winter half of the year a quarter of participants dropped below the deficiency threshold.
On top of that come factors that push the level down further, and they cluster remarkably often in the everyday life of women over 35:
- Working indoors The middle of the day, when synthesis would be most effective, is spent at a desk for most people. Window glass filters out UV-B completely. Office light is enough for your mood. It is not enough for vitamin D.
- Consistent sun protection Sensible for your skin, but sunscreen also reduces vitamin D synthesis substantially. That is not an argument against sun protection. It is an argument for keeping an eye on the level.
- Higher body weight Vitamin D is fat-soluble and is stored in fat tissue. With more body fat the same amount is distributed across a larger volume, so less of it shows up in the blood. Deficiency is measurably more common in this group.
- Age and skin tone The skin's capacity to produce vitamin D declines over the years. Darker skin also needs considerably longer sun exposure to produce the same amount.
None of these is a failure. They are simply the conditions many women live under today.
Vitamin D deficiency in women: the typical symptoms
Deficiency announces itself quietly. There is no single leading symptom that identifies it, only a pattern that builds over months and that many women recognise as a connection only in hindsight.
- Exhaustion that sleep does not improve The most common description. Not acute tiredness, but a flat baseline energy that persists for weeks. Strikingly often women report that late winter is the worst of it.
- Muscle weakness and muscle aches Vitamin D is directly involved in muscle function. Stairs feel harder, getting up from a squat feels heavier, and soreness after training lingers longer than it used to.
- More frequent infections Vitamin D takes part in regulating the immune system. One winter with three colds instead of one proves nothing on its own, but combined with the other points it is a signal worth following.
- Low mood through the dark months The evidence here is less clear-cut than it is often presented. The association exists, but the direction of cause is not settled. A low level does not explain a depressed mood on its own.
- Dull bone and joint pain Typically a deep, pressing ache, often in the lower back, the pelvis or the legs. It is hard to localise and frequently gets dismissed as tension.
And here lies the real difficulty. That list fits a low ferritin level just as well, and an underactive thyroid, and perimenopause. Test vitamin D alone and you may find a low value while missing the actual cause. Test nothing and you are guessing.
Photo: PNW Production / Pexels
Target levels: where deficiency actually begins
What gets measured is not vitamin D itself but its storage form, 25-hydroxyvitamin D. It reflects your supply over the preceding weeks, which makes it the most informative single value. On the lower threshold there is broad agreement. Above it, less so than most articles admit.
- Below 12 ng/mL (30 nmol/L) Deficiency. In this range the risk of consequences for bone health rises measurably. Guidelines agree on this cut-off, and it is the one that genuinely calls for action.
- 12 to 20 ng/mL (30 to 50 nmol/L) Insufficient supply. No acute deficiency, but no reserve either. This is the range a great many women sit in over winter.
- Above 20 ng/mL (50 nmol/L) Sufficient for bone health according to most public health bodies. The Endocrine Society, however, places sufficiency above 30 ng/mL (75 nmol/L), which is a real and unresolved difference.
The StatPearls chapter on vitamin D deficiency states the point plainly: the optimal blood concentration remains a matter of debate, and different organisations work with different cut-offs. To convert between units: ng/mL multiplied by 2.5 gives nmol/L.
This matters more than it sounds. The same result of 24 ng/mL is a normal finding under one guideline and an insufficiency under another. If a home-test provider uses the higher range, you receive a report flagging a problem that a doctor working to the lower threshold would not treat. That is not fraud. But it explains why so many women end up holding an alarming result that is, medically speaking, unremarkable.
Vitamin D, bone and perimenopause
Most articles on this subject treat vitamin D as a general wellness topic. For women between 35 and 55 there is a much more specific reason to pay attention right now.
Oestrogen protects bone. It restrains the cells that break bone down and supports the ones that build it up. When oestrogen starts fluctuating in perimenopause and then falls, that balance shifts. According to the StatPearls chapter on osteoporosis in females, bone mineral density drops by roughly 5 percent in the first year after menopause and by 1 to 1.5 percent per year in the years that follow.
Vitamin D plays one very specific role in this. It controls how much calcium the gut is able to absorb in the first place. Without enough vitamin D, even a calcium-rich diet achieves little, because the calcium never arrives. The two only work together. That is precisely why this stage of life is the moment the level becomes relevant, rather than at seventy.
The second component is mechanical. Bone responds to load. Pull and compression from working muscle are the strongest stimulus for bone formation there is. Vitamin D and structured strength training pull in the same direction here, and neither replaces the other.
Nina, 44, describes the blind spot that shows up so often with this topic: "Things started gradually: worse sleep, more restlessness, less energy. And everywhere I heard: that's just your age." Vitamin D is not the explanation for everything that changes in this phase. But it is one of the few factors that is simple to measure and simple to correct. That alone makes it worth checking, rather than filing it under "my age".
Photo: Ivan S / Pexels
How to raise a low vitamin D level
Sunlight, in the right window
From April to September, roughly ten to twenty minutes with face, arms and hands uncovered is enough in Central Europe, depending on skin tone, ideally around midday. Burning brings no advantage. Past a certain point the body stops production by itself, while the skin still takes the damage. Through the winter half of the year this route simply does not work here, no matter how much time you spend outdoors.
Food, with realistic expectations
Meaningful amounts come from oily fish such as salmon, herring and mackerel, plus egg yolk, liver and some mushrooms. It is a short list, and it is not enough. Most people take in only a few micrograms a day from food, a fraction of what the body needs once its own production drops away. Food is a supplement here, not a solution.
Supplements, when the sun is missing
Once a deficiency has been corrected, a daily maintenance dose in the range of 1,000 to 2,000 IU is commonly described for adults, with higher amounts for people at elevated risk. Treating a documented deficiency uses considerably higher doses over a defined period, typically around eight weeks, followed by a repeat test. That part belongs with a doctor, with a measured baseline and a follow-up value, not with a guess.
Two practical notes. Vitamin D is fat-soluble, so it is absorbed better alongside a meal containing some fat. And a daily dose is generally preferable to a high-dose weekly or monthly one, because it keeps the level steadier.
The FemBalance view: what vitamin D can and cannot do
This is the uncomfortable part, which is exactly why it belongs in this article. Over the past decade vitamin D has acquired a reputation the evidence does not fully support.
A meta-analysis in the EXCLI Journal pooled twelve randomised controlled trials with 7,765 participants in total and asked whether vitamin D supplementation improves muscle function in postmenopausal women. Handgrip strength, back strength and walking speed were measured. The result: no significant effect, in none of the three.
That is not an argument against vitamin D. It is an argument against a particular expectation. Correcting a deficiency is worthwhile and well evidenced, especially for bone. Topping up beyond the sufficient range does not make you stronger, sharper or more resilient. Most of these trials were run in women who were already adequately supplied, and that distinction is the one that almost always gets lost in the discussion.
My position on it is unspectacular and, I think, a relief: test the level when there is a reason to. Correct it if it is low. Then stop turning that particular dial. The energy that would otherwise go into the next stack of supplements is far better invested in sleep, strength training and protein intake. The tools that actually carry weight are the ones I have collected in my digital guides.
The key takeaways at a glance:
The symptoms are non-specific. Fatigue, muscle weakness, infections and bone pain also fit iron deficiency, thyroid problems and perimenopause.
What gets measured is 25-hydroxyvitamin D. Below 12 ng/mL is deficiency. Guidelines disagree on where sufficiency begins, at 20 or at 30 ng/mL.
From October to March UV-B is insufficient in Central Europe. Six in ten adults fall below the target level.
Around perimenopause the level becomes relevant, because oestrogen's protection of bone falls away and vitamin D governs calcium absorption.
After correction, 1,000 to 2,000 IU daily is the commonly described maintenance range. More than sufficient adds no further benefit.
Last updated: 15 September 2026
Frequently asked questions
What are the symptoms of vitamin D deficiency in women?
The typical pattern is persistent fatigue that sleep does not fix, muscle weakness and muscle aches, more frequent infections, low mood especially through the darker months, and dull, hard-to-localise bone or joint pain. Every one of these is non-specific and fits iron deficiency, an underactive thyroid or perimenopause just as well. Only a 25-hydroxyvitamin D blood test gives you certainty, not the symptom list.
What vitamin D level counts as deficient?
Below 12 ng/mL (30 nmol/L) is classed as deficiency, and guidelines agree on that threshold. Above it they diverge. Most public health bodies treat 20 ng/mL (50 nmol/L) as sufficient for bone health, while the Endocrine Society sets sufficiency above 30 ng/mL (75 nmol/L). This is why the same result can be labelled normal in one report and deficient in another. To convert: ng/mL multiplied by 2.5 gives nmol/L.
How long does it take to correct vitamin D deficiency?
Weeks to months, not days. Treatment protocols for genuine deficiency typically run over about eight weeks, after which the level is rechecked before moving to a maintenance dose. For milder insufficiency, retesting after roughly three months is the usual approach. The more depleted the starting point, the longer the refill takes.
How much vitamin D should a woman take daily?
Once a deficiency has been corrected, a daily maintenance dose in the range of 1,000 to 2,000 IU is commonly described for adults, with higher amounts for people at elevated risk. Higher loading doses used to treat a documented deficiency belong under medical supervision, with a measured baseline and a follow-up test. Without knowing your starting level, any number is guesswork.
Can you take too much vitamin D?
Not from sunlight, because the body limits its own production. From supplements, yes. A sustained excess can raise blood calcium, which puts strain on the kidneys and the heart. That is the reason high doses without a measured baseline and without follow-up testing are not a good idea. More is not better here, it is just more.
Should I get my vitamin D level tested?
Testing makes sense with persistent exhaustion, muscle symptoms, frequent infections, after a long stretch with little sun, or if osteoporosis runs in your family. As an annual routine with no symptoms it adds little. If you do test, late winter is the most informative timing, because that is when the level sits at its lowest point of the year.
This article is for general information and does not replace medical diagnosis or treatment. The ranges given are orientation values and do not apply to pregnancy, childhood, or existing conditions of the kidneys, parathyroid or calcium metabolism. Do not start high-dose vitamin D without a measured baseline level. If your results are abnormal or your symptoms persist, please speak to a doctor.
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