Vitamin D deficiency: symptoms, levels and what the Swedish winter does

What does vitamin D do in the body?

Vitamin D helps the gut absorb calcium and plays a central role for bones and muscles. The body gets it in two ways: it forms in the skin when sunlight reaches it, and it comes from food, mainly oily fish and fortified dairy products.

What makes vitamin D special in Sweden is that the sun route only works part of the year. The rest of the time, your level depends on diet, supplements and the store your body built up over the summer.

What are the symptoms of vitamin D deficiency?

Mild deficiency often causes no symptoms at all. When deficiency does cause problems, they tend to be vague: tiredness, muscle weakness, muscle aches and low mood. None of this is unique to vitamin D deficiency, which is exactly why the question is hard to settle without a test.

With long-standing, pronounced deficiency the skeleton can be affected. In adults this is called osteomalacia (softening of the bones), a condition investigated and treated within healthcare.

If the symptoms sound familiar, it makes sense to measure your level rather than guess. And since tiredness can just as easily come from iron or B12 deficiency, there is a point in looking at several values at once.

Which levels count as vitamin D deficiency?

Vitamin D status is measured as 25-OH-D (the storage form of vitamin D in blood). Swedish clinical references use the following classification:

| 25-OH-D level | Interpretation | | --- | --- | | Below 25 nmol per litre | Deficiency | | 25 to 50 nmol per litre | Insufficient level | | Above 50 nmol per litre | Sufficient for most people |

The cut-offs come from Swedish clinical guidance, and laboratories may use slightly different reference intervals. A value in the insufficient range does not automatically mean you need treatment; it is weighed together with symptoms and other results, and that assessment is a doctor's to make.

What does the Swedish winter do to vitamin D?

Skin makes vitamin D from UVB radiation, and north of roughly the 35th parallel that radiation is too weak during the winter months for any production to happen. All of Sweden lies far north of that line. During the Swedish winter, the skin therefore produces no vitamin D at all.

The body stores vitamin D, so what was made over the summer can cover part of the need through the winter half of the year. The rest has to come from food or supplements. This is why the Swedish Food Agency notes that supplements matter most during the winter half-year for the groups who need them, and that people who get plenty of sun can pause them from May to August.

Who is most at risk of vitamin D deficiency?

According to the Swedish Food Agency, some groups run a higher risk of getting too little vitamin D:

- People who are rarely out in the sun during summer, or who wear clothing covering the face, arms and legs - People with darker skin, since more pigment means it takes longer to produce the same amount of vitamin D - People who do not eat fish or vitamin D fortified foods - Everyone aged 75 and older

If you belong to one of these groups, the Swedish Food Agency recommends supplements, in most cases 10 or 20 micrograms per day depending on how many risk factors apply.

How do you get enough vitamin D?

The Swedish Food Agency recommends 10 micrograms of vitamin D per day for adults aged 18 to 74, and 20 micrograms per day for people 75 and older. Anyone with little or no sun exposure is advised to take a supplement year round: 10 micrograms per day if you eat fish and fortified foods, otherwise 20. Supplement labels sometimes state the amount in international units: 10 micrograms equals 400 IU.\n\nThe best food sources are oily fish such as salmon, herring and mackerel, along with fortified foods. In Sweden most milk products, plant drinks and cooking fats are fortified with vitamin D.\n\nThe Swedish Food Agency's upper limit for adults is 100 micrograms per day; staying below it is considered safe over time, and very high doses have no demonstrated benefit for otherwise healthy people.

How do you test your vitamin D?

Vitamin D status is measured with an ordinary blood test analysing 25-OH-D. No referral is needed; you order the test, walk in to a sampling location when it suits you, and receive the result digitally with an explanation of what the level means.

Since tiredness and low mood can just as well relate to B12 or folate, there is often value in measuring them in the same draw. If you then change your intake, a new test after a few months can show whether the level is moving the right way.

When should you see a doctor?

A blood test gives you a value, but not a diagnosis. See your doctor if you have long-lasting tiredness or aches affecting daily life, if your result shows pronounced deficiency, or if you have bone pain or muscle weakness that does not pass. The doctor can investigate the cause and decide whether and how a deficiency should be treated. When in doubt, you can always call 1177 for advice.

Vitamin Test Base measures vitamin D, B12 and folate in a single blood draw, no referral needed.

This article is general health information, not medical advice and not an assessment of your values. If you have symptoms or concerns, contact your healthcare provider.