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Welleo Editorial · 6 min read · Vitamin D / muscle pain / seasonality
There is a kind of pain that almost never gets a name. Diffuse muscle aches, soreness without having trained, heavy legs, difficulty getting up from a low chair. It gets put down to age, stress, poor sleep or posture. And in many cases there is a simpler explanation, one that can be measured.
A doctoral thesis from the University of Oviedo, led by Dr Carmen Fernández Milia with patients from Hospital de Cabueñes in Gijón, put numbers to that suspicion in 300 adult women.
KEY TAKEAWAYS
- In a study of 300 women aged 30 to 80 in the Gijón area, average vitamin D fell from 28.7 ng/ml in summer to 15.6 ng/ml in winter. That is a 45.6% drop in a matter of months.
- Only 3.6% of the women tested in winter had an optimal level, and almost one in four were below 10 ng/ml, the most severe deficiency range.
- Diffuse muscle pain, weakness getting up from a chair, or fatigue climbing stairs do not always come down to age or overexertion. Low vitamin D affects muscle fibre directly.
- In the clinical phase of the study, women with pain and low vitamin D who corrected their levels over six months under medical supervision improved significantly in both pain and functional capacity.
- This does not make vitamin D a painkiller. It means that before assuming where the pain is coming from, it is worth knowing your number.
Winter is not a detail: it takes almost half your vitamin D
Most of your vitamin D does not come from food. Your own skin makes it when sunlight reaches it, which is why levels rise and fall with the seasons.
In the study, the women tested during the sunnier period averaged 28.7 ng/ml. Those tested during the darker period averaged 15.6 ng/ml. A 45.6% drop.
The most striking figure is not that one, though. It is the summer one: even at the best time of year, only 16% of the women reached the level considered optimal, which starts at 30 ng/ml. In winter that fell to 3.6%. And almost one in four (24.9%) were below 10 ng/ml.
Put another way: in this population, low vitamin D is not the exception. It is the norm. And the month you get tested changes a great deal about what you will see.
Why deficiency shows up in muscle first
Vitamin D is not really a vitamin. It behaves like a hormone, and its receptor is involved in more than a thousand genes across the body, muscle tissue included.
When it stays low for a long time, muscle selectively loses the fibre type responsible for fast, forceful movement. The clinical picture is recognisable: weakness, a sense of wasting, and a diffuse musculoskeletal pain that does not sit in one specific place and does not show up on any scan.
That is why this kind of pain so often goes unexplained. There is nothing broken to see. What there is, is a biochemical deficiency that only a test will find.
The alarm your body sets off when vitamin D drops
The same study measured parathyroid hormone, PTH, which keeps blood calcium stable.
In winter, PTH was 21.1% higher than in summer (71.8 versus 59.3 pg/ml). That rise is not incidental: when vitamin D is not supplying enough calcium, the body takes it from where it is stored, which is bone.
That is what turns a low number on a lab report into something with real consequences over time.
What happened when levels were corrected
The final phase followed 91 women for six months. All of them met two conditions: pain of at least 4 out of 10, and vitamin D below 20 ng/ml. They were randomly assigned to three different medical treatment regimens.
Once vitamin D levels normalised, the improvement was statistically significant on two fronts: less pain on the 0 to 10 scale, and better muscle function, measured by how long it took them to stand up from a chair and by a functional capacity questionnaire.
It is worth reading this with the same honesty the study itself uses. It was run at a single hospital, and the three regimens compared were prescription medicines rather than food supplements. There was no placebo group either. What it shows solidly is an association between correcting the deficiency and feeling better, not that vitamin D is a treatment for pain.
What this study does not say
It does not say that taking vitamin D removes pain. In the European Union no food supplement may claim that at all. What is recognised is that vitamin D contributes to the maintenance of normal bones and to normal muscle function.
And above all, it does not say you should supplement blindly. The regimen that corrects a severe deficiency is not the same as a maintenance one, and the only way to know which one applies to you is to measure.
THE BOTTOM LINE
- If you have diffuse muscle pain with no clear cause, vitamin D is one of the first things worth ruling out, not the last.
- The month matters. A February result and an August result are not comparable, and if you have only ever tested in summer you may never have seen your worst figure.
- Test before you supplement. That is what separates a dose that makes sense from a guess.
- Retest a few months later, to see whether your levels have responded and whether the dose still fits.
- Talk to your doctor or pharmacist if your result comes back low, particularly if you also have pain or weakness.
If you have never tested your vitamin D in winter, you probably do not know your real level. The Welleo test is done at the pharmacy from a finger-prick sample and gives you a concrete starting point.
Find your nearest Welleo pharmacy
REFERENCES
- Fernández Milia C. Niveles de vitamina D en mujeres adultas y su relación con el dolor músculo-esquelético. Doctoral thesis. University of Oviedo, Department of Morphology and Cell Biology / Hospital de Cabueñes, Gijón.
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2011;96(7):1911-1930. DOI: 10.1210/jc.2011-0385
- European Food Safety Authority (EFSA). Dietary reference values for vitamin D. EFSA Journal. 2016;14(10):e04547. DOI: 10.2903/j.efsa.2016.4547
- European Commission. Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union. 2012;L 136:1-40.
