Vitamin D is really a hormone that the skin makes when UVB radiation hits it, and that the liver and kidneys then activate. It governs calcium uptake in the gut and thereby the skeleton, but vitamin D receptors are found in almost all cells: muscles (strength, recovery), immune cells (defence against respiratory infections, regulation of inflammation), the brain (mood), the pancreas and the heart. Severe deficiency gives rickets in children and osteomalacia in adults: the skeleton doesn't mineralise, becomes soft and aches, the muscles weaken (difficulty standing up from a chair, climbing stairs, a waddling gait), and fractures come easily. Moderate deficiency, which is the common kind, is quieter: tiredness, diffuse muscle aches and weakness, bone pain (often shins, lower back, pelvis, ribs; tender when you press on the bone), low mood in winter, more infections, poorer healing and over time osteoporosis. In the Nordics no vitamin D is made in the skin from October to March, whatever the weather, because the sun is too low; in summer 15–30 minutes with arms and legs in the midday sun a few times a week is enough for fair-skinned people, but sunscreen, shade, clothing and darker skin reduce production greatly, and the body stores vitamin D for only a few months. The diet normally gives 5–7 micrograms a day (oily fish, eggs, fortified dairy and plant drinks, spreads), while the recommendation is 10 micrograms (400 IU) for adults and 20 micrograms (800 IU) for everyone over 75 and for risk groups. That is why a third of Swedish adults have low levels in winter, and considerably more in the risk groups.
The symptoms of vitamin D deficiency, and what resembles them
| Symptom | With vitamin D deficiency | Also resembles |
|---|---|---|
| Tiredness | Diffuse, worst in winter, better in summer | Iron deficiency, thyroid, sleep deprivation, depression, B12 deficiency |
| Muscle aches and weakness | Symmetrical, in thighs, upper arms, back; difficulty standing up, climbing stairs; no swelling | Fibromyalgia, myalgia, statin side effect, polymyalgia rheumatica (over 60, with high ESR), hypothyroidism |
| Bone pain | Deep, dull ache in shins, lower back, pelvis, ribs; tender when you press on the bone | Osteoarthritis, osteoporosis with vertebral compression, muscle soreness, rheumatism |
| Low mood | Seasonal, November–March | Seasonal affective disorder (lack of light itself), depression, burnout |
| Infections | More and longer respiratory infections | Sleep deprivation, stress, smoking, exposure |
| Fractures, bone that gives way | Osteoporosis, osteomalacia | Osteoporosis from other causes |
| Hair loss, wounds that heal slowly, cramps and tingling (with very low calcium) | Severe deficiency | Many other causes |
None of the symptoms is specific, and most tired people don't have vitamin D deficiency. So: a test for those in a risk group or with symptoms, and not supplements blindly in high doses. See also fatigue: causes and what helps and muscle aches.
Who gets deficient in the Nordics?
- Dark skin: melanin blocks UVB; dark-skinned people need three to six times longer in the sun for the same production, and in the Nordics that isn't enough. The largest risk group.
- Covering clothing for religious, cultural or occupational reasons, and those who always use sunscreen or stay in the shade.
- Rarely outdoors: indoor work, older people in care homes, the long-term ill, night shift work.
- Over 70: the skin makes a quarter as much vitamin D as in a 20-year-old, and the kidneys activate it less well.
- Overweight: vitamin D is stored in fat tissue and doesn't reach the blood; the need is often double.
- Gut disease: coeliac disease, Crohn's, ulcerative colitis, after bariatric surgery, gallbladder disease, chronic pancreatitis: fat-soluble vitamins are poorly absorbed.
- Medicines: antiepileptics, cortisone, some HIV and antifungal drugs, orlistat, colestyramine.
- Pregnant and breastfeeding women with little sun or dark skin; infants (vitamin D drops for all children under two).
- Kidney disease, liver disease, hyperparathyroidism and conditions such as osteoporosis where the level should be optimal.
- A vegan diet without fortified products, and those who don't eat fish.
When to get tested, and what the numbers mean
The test is called 25-hydroxyvitamin D (25-OH-D) and is taken at your doctor's for symptoms in someone in a risk group, for osteoporosis, for unexplained muscle aches or bone pain, for gut disease, before treatment with osteoporosis medicines, and sometimes in a fatigue work-up. Screening of healthy people without risk factors isn't recommended. Below 25 nmol/l is severe deficiency and is treated with high doses under medical supervision (often 50–100 micrograms a day for three months, or weekly doses, then maintenance). 25–50 nmol/l is deficiency or an insufficient level and is treated with 20–50 micrograms a day. 50–75 nmol/l is sufficient for the skeleton; some guidelines aim for over 75 with osteoporosis and other diseases. Over 125 nmol/l gives no extra benefit and over 250 is a risk of toxicity. Take the test in winter if you want to know your lowest value, and repeat it after three to four months of treatment. Calcium and PTH are often taken at the same time.
How much vitamin D is enough, and how much is too much?
- Healthy adults with normal sun in summer: 10 micrograms (400 IU) a day from diet and if needed supplements, especially October to March. Many get it from fortified milk, spreads and fish twice a week; those who don't take a tablet.
- Risk groups and everyone over 75: 20 micrograms (800 IU) a day all year round, according to the Swedish Food Agency. Dark skin, covering clothing, little sun, overweight: the same.
- With proven deficiency: the dose the doctor prescribes, usually 20–50 micrograms a day (800–2,000 IU) or a high-dose course, followed by maintenance. Take it with a fat-rich meal: absorption more than doubles.
- Upper safe limit: 100 micrograms (4,000 IU) a day for adults without medical supervision. Higher doses for months cause hypercalcaemia: nausea, thirst, constipation, kidney stones, heart rhythm disturbances and confusion. Vitamin D toxicity never comes from sun (the skin regulates) but only from supplements, and "megadoses" such as 10,000 IU daily sold online aren't safer for being popular.
- D3 (cholecalciferol) raises the level better than D2 and is standard; drops, tablets and spray work equally well; K2 doesn't need to be added despite the marketing. Calcium supplements only with low calcium intake from the diet.
- Sun: April to September, 15–30 minutes at midday with arms and legs bare, a few times a week, without burning, gives fair-skinned people a store for autumn; dark-skinned people need much more and should count on supplements. Sunbeds aren't recommended for vitamin D (skin cancer risk).
- Diet: oily fish (salmon, mackerel, herring, 100 g gives 10–20 micrograms), eggs (1 microgram), fortified milk, yoghurt, plant drinks and spreads (1–2 micrograms per portion), chanterelles and sun-exposed mushrooms. It is hard to reach 10 micrograms from the diet without fish and fortified products.
Vitamin D, muscles, bones and recovery
Muscle cells have vitamin D receptors that govern protein synthesis, calcium handling and the function of the fast muscle fibres. With deficiency the muscles become weaker and more tired, recovery after training slower, and the fall risk in older people increases; studies on older people with deficiency show better strength, balance and fewer falls after supplements, and studies on athletes with low levels show better muscle function and fewer stress fractures after correction. In those with normal levels, extra vitamin D gives no extra strength or performance: the effect exists only with deficiency. For the skeleton, vitamin D together with calcium and loading is what keeps the bone mineralised, and with osteoporosis the level should be kept above 50–75 nmol/l; see osteoporosis. For the immune system, supplements reduce respiratory infections in those with deficiency, not in those with normal levels; see strengthen the immune system. And for the muscle aches that are one of the most common symptoms: cupping, massage and heat relieve the ache in the moment through increased blood flow and relaxation, and light cupping of thighs, upper arms and back two to three times a week is a reasonable way to keep moving during the months it takes to refill the stores, but the ache only disappears once the deficiency is corrected, so get the test. With osteomalacia and tender bones: light suction, not over tender bones, and no hard massage until the level is normal. More in muscle aches and cupping at home.
Read more
Fatigue: causes and what helps, muscle aches, osteoporosis, strengthen the immune system, fibromyalgia, restless legs, numbness in the feet and sleep deprivation.
Frequently asked questions
What are the symptoms of vitamin D deficiency?
Tiredness that is worst in winter, diffuse muscle aches and weakness in thighs, upper arms and back (difficulty standing up and climbing stairs), a dull ache in the bones (shins, lower back, pelvis, ribs, tender when you press), low mood November to March, more and longer respiratory infections, and over time osteoporosis and fractures. No symptom is specific, so get tested if you belong to a risk group or have the symptoms; iron deficiency, thyroid and sleep deprivation give a similar picture.
How much vitamin D should you take?
10 micrograms (400 IU) a day for healthy adults, from diet and if needed supplements, especially October to March; 20 micrograms (800 IU) all year round for everyone over 75 and for risk groups (dark skin, covering clothing, little sun, overweight, gut disease). With proven deficiency the dose the doctor prescribes, often 20–50 micrograms. The upper safe limit without medical supervision is 100 micrograms (4,000 IU) a day; more for months can cause toxicity. Take it with a fat-rich meal.
Who should get a vitamin D test?
Those with symptoms who belong to a risk group (dark skin, covering clothing, rarely outdoors, over 70, overweight, gut disease, certain medicines), those with osteoporosis, unexplained muscle aches or bone pain, and sometimes in a fatigue work-up. The test is called 25-OH-D: below 25 nmol/l is severe deficiency, 25–50 deficiency, over 50 sufficient. Screening of healthy people without risk factors isn't recommended. Repeat the test after three to four months of treatment.
Do you get vitamin D from the sun in winter in the Nordics?
No. From October to March the sun is so low that UVB doesn't reach the skin in sufficient amounts, whatever the weather and however much you are outdoors. In summer 15–30 minutes at midday with arms and legs bare a few times a week is enough for fair-skinned people, but the store lasts only a few months. Dark-skinned people need three to six times longer and should count on supplements all year. Sunbeds aren't recommended.
Does vitamin D help muscle aches and tiredness?
Yes, if you are deficient: muscle strength, tiredness, aches and fall risk improve within a few months once the level is normalised, and older people with deficiency get better balance and fewer falls. If the level is already normal, extra vitamin D gives nothing. While the stores are being refilled, cupping, massage, heat and light movement relieve the muscle aches in the moment, but the ache only disappears once the deficiency is corrected; get the test instead of guessing.
Related guides
- Iron deficiency – symptoms, ferritin and what helps
- B12 deficiency – symptoms, who gets it and treatment
Written by Curam. Last updated 17 October 2026. This is general self-care information and does not replace medical care. For sudden, severe or unusual symptoms, contact your doctor. Talk to your doctor before cupping if you are pregnant, take blood thinners or have a condition affecting skin, blood vessels or blood.
