Quick version
Vitamin D is important for bones, muscles and physical function, but deficiency often causes diffuse symptoms such as fatigue, muscle weakness and aches. The risk of low levels increases with limited sun exposure, old age, dark skin or conditions that affect the body's absorption of nutrients. Fatty fish and fortified foods are the main dietary sources, but some people may need supplements. Since the symptoms of vitamin D deficiency are non-specific and can have many different causes, it is often better to rely on testing and a comprehensive assessment of health and lifestyle than to guess.
Fatigue that doesn't quite go away, diffuse body aches or recurring muscle weakness make many people wonder if it could be a vitamin D deficiency. The question often comes up during the winter months, but the answer is rarely as simple as just "eating a little better". Vitamin D is affected by diet, sunlight, skin type, age and how the body absorbs nutrients.
Signs of vitamin D deficiency - which food contains the most vitamin D?
What signs of vitamin D deficiency are noticeable in the body?
Mild vitamin D deficiency often does not cause any noticeable symptoms. This is one reason why many people remain unaware of their vitamin D status for a long time. However, when the deficiency becomes more severe, it can affect both bone and muscle health.
In adults, symptoms of vitamin D deficiency may include muscle weakness, bone tenderness, diffuse pain in the back, pelvis, or legs, and increased sensitivity to stress. Severe and prolonged deficiency can lead to osteomalacia, a condition in which the bones become inadequately mineralized and softer than normal. This can result in pain, reduced physical function, and, in some cases, an increased risk of fractures.
Many people first seek treatment because they have become unusually tired. Fatigue is common in many conditions and is not specific to Vitamin D deficiency,, but together with muscle weakness, low sun exposure or a one-sided diet, it can be a reasonable part of the overall picture. Therefore, the symptoms always need to be interpreted in context, not in isolation.
Vitamin D deficiency can be linked to muscle weakness, impaired physical function, increased fatigue and poorer recovery after physical activity, among other things. Older people may also experience increased unsteadiness and pain. These symptoms can be affected by vitamin D status, but often have several different underlying causes.
Why does vitamin D deficiency occur?
Vitamin D is produced in the skin when it is exposed to UVB radiation from sunlight. However, the amount produced varies considerably depending on the season, the extent of skin exposure, age, and the amount of time spent outdoors. Diet also contributes to vitamin D levels, but relatively few foods naturally contain significant amounts of the vitamin. As a result, it is difficult to assess your vitamin D status based solely on dietary intake.
The risk of deficiency increases in individuals who have limited sun exposure, cover most of their skin when outdoors, or have darker skin, as higher levels of pigmentation reduce the skin’s ability to produce vitamin D. Older adults are also at greater risk because the skin becomes less efficient at synthesizing vitamin D with age. In addition, people who are underweight, malnourished, or have conditions that impair intestinal absorption may be more likely to develop a deficiency.
Certain medications and medical conditions can also affect vitamin D levels. Examples include inflammatory bowel disease, bariatric surgery, chronic kidney disease, and long-term corticosteroid therapy. In such cases, vitamin D status may need to be monitored more closely by healthcare professionals. This also helps explain why two individuals with similar diets can have markedly different vitamin D levels.
For employers, this is relevant from a preventive health perspective. Nonspecific symptoms such as fatigue, low energy levels, and musculoskeletal pain can affect both well-being and work performance, but they should be assessed systematically. A health assessment can help distinguish between lifestyle-related factors, nutritional deficiencies, and other underlying medical conditions.
Which food contains the most vitamin D?
When asked which foods contain the most vitamin D, the answer is clear: fatty fish are among the richest natural sources. Salmon, trout, mackerel, and sardines contain significantly higher amounts of vitamin D than most other commonly consumed foods. Cod liver oil is also exceptionally rich in vitamin D, although it is less commonly consumed as part of the regular diet.
Other animal-based foods, such as egg yolks and liver, contain vitamin D as well, but in considerably smaller amounts. Cheese provides only limited amounts. Mushrooms can contribute to vitamin D intake, particularly if they have been exposed to UV light, although their vitamin D content varies substantially between products.
In Sweden, fortified foods play an important role in maintaining adequate vitamin D intake. Certain milk products, fermented dairy products, plant-based alternatives, and edible fats are fortified with vitamin D, making them valuable dietary sources even though they contain less vitamin D per serving than fatty fish. For many people, it is the combination of occasional fish consumption and the daily intake of fortified staple foods that determines whether vitamin D intake is sufficient.
Examples of foods that can contribute vitamin D are:
Fatty fish such as salmon, trout, mackerel and sardines
Enriched milk, filbert and yoghurt
Enriched plant drinks
Enriched fats and margarines
Eggs
UV-treated mushrooms
Is food enough, or are supplements and testing needed?
For many healthy adults under the age of 75, routine supplementation with doses above the recommended daily intake is generally not advised. International guidelines also recommend against routine screening for vitamin D deficiency in healthy individuals without specific risk factors. However, supplementation may be more appropriate for certain groups, including older adults, people with very limited sun exposure, and those at increased risk of low vitamin D levels.
Most adults and children require approximately 10 micrograms of vitamin D per day, while adults over the age of 75 are generally recommended to consume around 20 micrograms daily. For individuals who do not eat fish or fortified foods, or who rarely spend time outdoors in sunlight, vitamin D supplementation may be beneficial. The same applies to people who cover most of their skin throughout the year for medical, cultural, or religious reasons.
The blood test used to assess vitamin D status is 25-OH-vitamin D, also called 25-hydroxyvitamin D. It is the best marker of the body's total vitamin D level from both sunlight, diet and supplements. Reference frames increase the risk of deficiency at levels below 30 nmol/L, while 75 nmol/L or more is considered sufficient for most people.
If you have verified deficiency and symptoms, treatment should often be followed up after about three months. This is because the body needs time to reach a new stable level. Starting with high doses on your own without knowing the starting point is less wise, since excessively high levels can also be harmful.
When should you suspect vitamin D deficiency and get it checked?
There are special situations where it is reasonable to consider testing. This applies especially if you have symptoms such as muscle weakness or bone pain and at the same time belong to a risk group, or if you already have a condition where bone health is central, such as osteoporosis. In those cases, testing makes more sense than guessing.
It is also wise to think more broadly than just vitamin D. Fatigue, aches and decreased energy can be due to iron deficiency, B12 deficiency, thyroid disorder, lack of sleep, stress or low energy availability. Therefore, a more complete checkup often provides greater value than a single test, especially if the symptoms have several possible causes.
For those who exercise a lot, work shifts, eat vegan or rarely spend time outside in daylight, a test can be a way to get a clear starting point. Vitamin D is not just about a single vitamin, but about how the skeleton, muscles, lifestyle and daily routines interact over time. This is why it is often more helpful to measure than to assume, especially when the symptoms are vague but recurring.
