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A brief overview of common vitamin deficiencies
Vitamin B12 deficiency can cause fatigue, numbness, tingling, balance problems and memory difficulties. It may be caused by an inadequate dietary intake, certain medicines or impaired absorption in the stomach or intestines.
Folate deficiency can cause fatigue, pale skin and anaemia. Folate levels should often be assessed together with vitamin B12.
Vitamin D deficiency can contribute to muscle weakness, widespread aches and impaired bone health, particularly in people with limited sun exposure.
Vitamin deficiencies are usually investigated using blood tests. In some cases, additional tests are needed to confirm the deficiency or identify its cause.
Because these symptoms can have several possible causes, vitamin tests are often combined with other analyses, such as a complete blood count, iron status and thyroid tests.
If you have persistent or pronounced symptoms, it is often advisable to test your vitamin levels before starting supplements.
Many people experience fatigue, difficulty concentrating, numbness, muscle pain or recurring mouth ulcers for a long time without knowing what is causing their symptoms. Possible causes include stress, lack of sleep or an underlying medical condition – but sometimes the explanation is a vitamin deficiency. A blood test can help determine whether you have low levels of vitamins such as vitamin B12, folate or vitamin D, and whether your symptoms may be related to your nutritional status.
Vitamin deficiency tests – an overview of common deficiencies
A vitamin deficiency means that the body has insufficient levels of a vitamin needed for normal cell function, nerve function, blood formation, immune function or bone health. Some deficiencies develop quickly, while others emerge gradually over months or years.
It is also important to distinguish between symptoms and their underlying cause. A low vitamin level may be caused by an inadequate dietary intake, but it can also occur when the body is unable to absorb the vitamin properly. Therefore, vitamin deficiency testing is not simply about measuring a single value. The result should be interpreted alongside symptoms, risk factors and, in some cases, other blood test results.
The vitamin deficiencies most commonly investigated in adults include:
Less common deficiencies, such as vitamin C deficiency, can also occur, although they are considerably less common in high-income countries. Some symptoms may also overlap with iron deficiency, thyroid disorders, inflammatory conditions or stress-related health problems. It is therefore often helpful to view vitamin deficiency testing as part of a broader health assessment.
Three common vitamin deficiencies and their causes
Vitamin B12
Vitamin B12 is essential for the nervous system, DNA synthesis and the production of red blood cells. A deficiency can cause fatigue, low energy, shortness of breath, palpitations, tingling or numbness in the hands and feet, balance problems, memory difficulties, low mood and a sore or red tongue. Vitamin B12 deficiency can occur with or without obvious anaemia. Common causes include impaired absorption in the stomach or intestines, autoimmune conditions that affect intrinsic factor, previous stomach or intestinal surgery, coeliac disease, inflammatory bowel disease, older age and long-term treatment with medicines such as metformin or proton pump inhibitors. Following a vegan diet without taking supplements is also a clear risk factor.
Folate
Folate is needed for cell division and blood formation. Folate deficiency can cause fatigue, pale skin, shortness of breath, tongue symptoms and anaemia. It may be caused by a low dietary intake, high alcohol consumption, malabsorption, pregnancy, certain medicines or an increased need for folate. A suspected folate deficiency should not be treated without also assessing vitamin B12 levels. Otherwise, folic acid treatment may mask a simultaneous B12 deficiency while neurological damage continues to develop.
Vitamin D
Vitamin D plays an important role in calcium metabolism, muscle function and bone health. A severe deficiency can contribute to osteomalacia in adults, which means that the bones are not mineralised properly. This can cause widespread bone pain, muscle weakness and an increased risk of falls. The risk is higher among people with limited sun exposure, darker skin, clothing that covers most of the skin, older age, certain intestinal conditions or other causes of malabsorption. Vitamin D deficiency is often considered in people with persistent fatigue and aches, but these symptoms are non-specific and can have many other causes.
Vitamin C deficiency is less common. A prolonged and severely inadequate intake can cause scurvy, with symptoms including fatigue, bleeding gums, small areas of bleeding beneath the skin, joint pain and poor wound healing. Although uncommon, it can occur in people with a very restricted diet, alcohol dependence or severe malnutrition.
How do vitamin deficiency tests work?
Most vitamin deficiencies are investigated using blood tests. The most appropriate test depends on which deficiency is suspected.
If vitamin B12 deficiency is suspected, serum B12 is often used as the initial test. If the result is borderline or the symptoms strongly suggest a deficiency, additional testing may include methylmalonic acid (MMA) or, in some cases, homocysteine. These markers can help confirm functional B12 deficiency.
If B12 deficiency is confirmed or strongly suspected, further tests may sometimes be used to identify the cause. For example, antibodies against intrinsic factor may be measured when an underlying autoimmune condition is suspected. Identifying the cause can be important because it may affect both treatment and the need for ongoing follow-up.
If folate deficiency is suspected, folate is usually measured in a blood sample, often as serum folate. A complete blood count is also often assessed, particularly haemoglobin and the size of the red blood cells, as folate deficiency can cause macrocytic anaemia. However, folate levels should be interpreted alongside symptoms and other test results rather than in isolation.
If vitamin D deficiency is suspected, the standard test is 25-hydroxyvitamin D, often written as 25(OH)D. This is the best available marker of the body's vitamin D status.
Vitamin deficiency tests are often combined with other analyses to provide a more meaningful overall picture, such as:
complete blood count
folate and vitamin B12 together
in some cases, calcium and kidney function tests
This may be particularly relevant when symptoms are non-specific. Fatigue, for example, can be caused by vitamin B12 deficiency, folate deficiency, iron deficiency, hypothyroidism, lack of sleep or depression. The more complete the assessment, the more useful the test results are likely to be.
When may it be appropriate to test for a vitamin deficiency?
If you have symptoms that could be caused by a vitamin deficiency or another nutritional deficiency, testing may help provide more information about your nutritional status. It may be appropriate to consider a vitamin deficiency test if you:
have felt unusually tired or low in energy for a prolonged period
experience tingling, numbness or balance problems
have muscle weakness, widespread aches or bone pain
have recurring tongue soreness, mouth ulcers or pale skin
follow a vegan or highly restricted diet
have undergone stomach surgery or bariatric surgery
have coeliac disease, inflammatory bowel disease or another condition that causes malabsorption
have used metformin or acid-suppressing medicines for a long time
are older and have a poor appetite or low food intake
are pregnant or planning a pregnancy, particularly in relation to folate and, depending on your risk profile, vitamin B12 or vitamin D
What happens if a vitamin deficiency test shows low levels?
If a test identifies a deficiency, the next step is to determine how severe it is, whether it may explain the symptoms and why it has developed. Treatment depends on both the vitamin involved and the underlying cause:
Vitamin B12 deficiency may be treated with tablets or injections, depending on the cause, the severity of the deficiency and whether neurological symptoms are present.
Folate deficiency is usually treated with folic acid, but vitamin B12 deficiency should be assessed first.
Vitamin D deficiency is usually treated with supplements, sometimes at a higher dose for a limited period followed by a maintenance dose.
If the deficiency is related to diet, a dietary review and, in some cases, long-term supplementation may be needed.
If the deficiency is caused by malabsorption or an autoimmune condition, further medical investigation and follow-up may be required.
When vitamin B12 deficiency causes neurological symptoms, timely treatment is particularly important. Otherwise, nerve damage may become long-lasting and, in some cases, may not fully resolve.
Frequently asked questions about vitamin deficiencies
Can I test for several vitamin deficiencies at the same time?
Yes. Combining tests is often helpful, particularly when symptoms are non-specific. For example, measuring vitamin B12, folate and vitamin D together with a complete blood count can provide a clearer picture than a single test.
Can I simply start taking supplements?
Not always. If you have clear symptoms or long-lasting health problems, it is often better to test first. Otherwise, you may miss the underlying cause or temporarily normalise a value without understanding the broader picture.
Can I have a healthy diet and still develop a vitamin deficiency?
Yes. Vitamin B12 deficiency, in particular, may be caused by absorption problems rather than an inadequate intake. This can occur with conditions such as autoimmune gastritis or coeliac disease, or after gastric bypass surgery.
When should I seek medical care rather than only taking a test?
Seek medical care if you experience severe shortness of breath, chest pain, rapid deterioration, clear neurological symptoms such as difficulty walking or loss of sensation, blood in your stools, unexplained weight loss or a marked decline in your general condition.
Would you like a better understanding of what may be causing your symptoms?
At Testmottagningen, you can test individual vitamins, choose a package that includes common vitamins and minerals or undergo a more comprehensive health check. A comprehensive health check may also include analyses such as a complete blood count, iron status, thyroid function and kidney function. This can provide a broader basis for assessment when symptoms are vague and may have several possible causes.
