What are the symptoms of vitamin D deficiency?

Mild deficiency often causes no noticeable symptoms. Severe deficiency can cause muscle weakness, particularly in the large muscles around the hips and thighs, making it harder to rise from a chair or climb stairs, and some people experience diffuse pain in muscles and bones. Such symptoms can have many other causes, however.

How much vitamin D do adults need per day?

Adults under 75 years are recommended 10 micrograms a day, while people over 75 years are recommended 20 micrograms.

Which foods contain the most vitamin D?

Fatty fish are the best sources: herring provides 10–15 micrograms per 100 g, trout 5–15, salmon 5–12 and mackerel 5–10. Cod liver oil gives 10 micrograms per 5 ml, an egg 1–1.5 micrograms, and fortified milk 0.8–2 micrograms per 2 dl. The amounts are approximate and vary between products.

Does vitamin D protect against colds and flu?

Research has investigated whether supplementation can reduce the risk of respiratory infections, but the results vary. There is no basis for claiming that extra vitamin D generally prevents colds or flu in people who already have sufficient levels.

When should you have your vitamin D level tested?

If deficiency is suspected, a doctor may consider a blood test measuring 25-hydroxyvitamin D. Testing is particularly relevant with symptoms, diseases that reduce nutrient absorption, or other risk factors. Routine testing of all healthy people is not recommended.

Too Little Vitamin D? Here's How It Affects Muscles, Bones, and the Immune System | Hardworkout Magazine

Key takeaways

- Adults under 75 are recommended 10 micrograms of vitamin D a day, while those over 75 are recommended 20 micrograms.

- From roughly October to March, the sun in Norway sits too low for the skin to produce meaningful amounts of vitamin D, making diet and supplements the main sources.

- Severe, long-term vitamin D deficiency can cause osteomalacia in adults and rickets in children, because reduced calcium absorption leaves the skeleton poorly mineralised.

- A single 100 g serving of fatty fish, or 5 ml of cod liver oil, can cover an adult's entire daily vitamin D requirement.

- Excessive vitamin D intake over time can raise blood calcium levels and, in severe cases, damage the kidneys.

Vitamin D differs from most other vitamins in that the body can produce it itself when the skin is exposed to sunlight. However, in Norway, this production is very limited for large parts of the year. This makes us dependent on getting enough through our diet, which is not always straightforward.

What actually happens in the body when levels become too low, and how much is needed before deficiency has consequences for health?

Why does the body need vitamin D?

Vitamin D is a fat-soluble vitamin that regulates the absorption of calcium and phosphate from the intestine. Both minerals are necessary for building and maintaining a strong skeleton.

The vitamin also plays a role in muscle function and the immune system.

Vitamin D affects both the innate immune system, which responds quickly to pathogens, and the adaptive immune system, which develops more targeted responses.

Among other things, the vitamin helps regulate the activity of various immune cells and the production of antimicrobial proteins that protect against bacteria and viruses.

It also affects signaling molecules that control inflammatory responses, allowing the immune system to respond to infections without creating unnecessarily strong inflammatory reactions.

What happens with vitamin D deficiency?

The consequences depend on how severe the deficiency is and how long it lasts.

Mild deficiency often shows no noticeable symptoms, while long-term or severe deficiency can lead to several problems.

Weaker skeleton

When the body receives too little vitamin D, the absorption of calcium from the intestines is reduced. With long-term deficiency, this can lead to the skeleton not being mineralized normally.

In adults, severe deficiency can lead to osteomalacia, a condition where the bones become softer and can cause pain and increased risk of fractures. In children, deficiency can lead to rickets, which affects the development of the skeleton.

Muscle Weakness and Pain

Severe vitamin D deficiency can cause muscle weakness, especially in the large muscles around the hips and thighs. It can become more difficult to rise from a chair or climb stairs.

Some also experience diffuse pain in muscles and bones. However, such symptoms can have many other causes and do not necessarily mean that you are lacking in vitamin D.

Impact on the Immune System

Vitamin D deficiency can affect how the immune system responds to pathogens and regulates inflammatory responses.

Research has investigated whether supplementation can reduce the risk of respiratory infections. The results vary, and there is no basis for claiming that extra vitamin D generally prevents colds or flu in individuals who already have sufficient levels.

Why is deficiency more common in winter?

In Norway, the sun is too low for the skin to produce significant amounts of vitamin D for large parts of the winter season.

From about October to March, we are therefore particularly dependent on vitamin D from food and any supplements.

Who is most at risk of vitamin D deficiency?

The risk of deficiency is greater among individuals who consume little vitamin D through their diet, have dark skin, spend little time outdoors, or cover large parts of their skin with clothing.

Older adults may also be more susceptible because the skin's ability to produce vitamin D decreases with age.

![Good sources of vitamin D in the diet](https://hardworkout.no/wp-content/uploads/2026/10/Vitamin-D-rikt-matfat-med-laks-og-fisk.png)

How to get enough vitamin D

Fatty fish such as salmon, trout, mackerel, and herring are among the best sources of vitamin D. Cod liver oil also contains a lot, while eggs and certain fortified dairy products and plant-based drinks contribute smaller amounts.

How much vitamin D is in salmon, eggs and cod liver oil?

Here are some examples of how much vitamin D various foods contain:

- Salmon, 100 g: 5-12 micrograms

- Trout, 100 g: 5-15 micrograms

- Mackerel, 100 g: 5-10 micrograms

- Herring, 100 g: 10-15 micrograms

- Egg, 1 piece: 1-1.5 micrograms

- Cod liver oil, 5 ml: 10 micrograms

- Fortified milk, 2 dl: 0.8-2 micrograms

The amounts are approximate and can vary between different products.

For adults under 75 years, a daily intake of 10 micrograms of vitamin D is recommended, while individuals over 75 years are recommended 20 micrograms.

A serving of fatty fish can thus cover the entire daily requirement, while a teaspoon of cod liver oil usually provides 10 micrograms. You do not need to consume exactly the same amount every day, as the body can store vitamin D.

If you eat little fatty fish or get little vitamin D through your diet, a supplement may be appropriate. Check the content if you combine cod liver oil with other vitamin supplements, so you do not get unnecessarily high doses.

Can you get too much vitamin D?

Excessive amounts of vitamin D over time can lead to elevated calcium levels in the blood and, in severe cases, damage the kidneys.

When should you check your vitamin D levels?

If there is suspicion of deficiency, the doctor may consider a blood test that measures 25-hydroxyvitamin D.

Testing is particularly relevant in the presence of symptoms, diseases that reduce nutrient absorption, or other risk factors. Routine testing of all healthy individuals is not recommended.

An adequate intake of vitamin D is important throughout the year but requires extra attention during the winter. A varied diet with good sources of vitamin D, along with supplements if needed, is usually sufficient to prevent deficiency.

![Vitamin D](https://hardworkout.no/wp-content/uploads/2019/04/AdobeStock145730503-1.jpeg)

Sources:

Vitamin D – [National Institutes of Health](https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/)