Quick version
A vegetarian diet is healthy, but some nutrients are less well absorbed from plant foods. To avoid deficiencies, you should primarily check vitamin B12 (nerve function and blood formation) and ferritin (the body's iron stores). Vitamin D, thyroid tests (in case of low iodine intake) and zinc are also important to monitor. Checking is especially relevant in the case of a long-term vegetarian diet, pregnancy or symptoms such as fatigue and numbness.
Many people who eat vegetarian food feel great and get most of what they need through their food. At the same time, it is common to wonder whether certain nutrients are really enough in the long run. The question of which markers are important to check if I am a vegetarian is therefore very relevant. A well-planned vegetarian diet can be nutritionally complete, but certain vitamins and minerals require extra attention because they are found in smaller quantities in vegetarian food or are absorbed less well from the plant kingdom.
Which markers are important to check if I am a vegetarian?
If you are a vegetarian, it is above all wise to follow markers that reflect blood formation, nerve function, thyroid conditions and skeletal health. The most important thing is not to “take all the tests”, but to choose markers that actually say something about the risk of deficiency. For most vegetarians, vitamin B12, iron status, vitamin D and sometimes iodine, zinc and folate are most relevant. How often you should test depends on how you eat, whether you use supplements, whether you have symptoms and whether you belong to a group at increased risk, such as fertile women, pregnant women, the elderly or people with gastrointestinal disease.
Vitamin B12 – the most important marker for many vegetarians
Vitamin B12 is often the most central marker to check in a vegetarian diet. B12 is needed for the nervous system, blood formation and cell metabolism. The risk of low levels is greatest in vegans, but lacto-ovo vegetarians can also get too little over time, especially if their intake of dairy products and eggs is low. Official dietary guidelines for vegetarians therefore emphasize the need for a safe source of B12, either through animal foods, fortified products or supplements.
Common symptoms of B12 deficiency can be:
fatigue and decreased energy
tingling or numbness in the hands and feet
memory problems or concentration problems
pallor
dizziness
glossitis, i.e. burning or soreness of the tongue
The tricky thing is that B12 deficiency is not always clearly visible at first. A common misconception is that a “normal” B12 test always rules out deficiency. This is not the case. Serum B12 can be difficult to interpret, especially at borderline values. Therefore, it may be wise to supplement with functional markers such as methylmalonate (MMA) and sometimes homocysteine if suspicion is high or if B12 is in the gray area. Holotranscobalamin, sometimes called active B12, can also provide more information early in the course.
In practice, the following blood tests are often most useful:
Vitamin B12 in serum
Holotranscobalamin (active B12), if available
Methylmalonate (MMA) in case of unclear or borderline results
Homocysteine as a supplementary marker
Blood status, especially hemoglobin and MCV, since B12 deficiency can cause large-celled red blood cells
For those who eat strictly plant-based for a long time, B12 is almost always a marker that should be monitored regularly.
Iron status and ferritin – especially important in case of fatigue, menstruation or training
Iron is another area where vegetarians sometimes need extra attention. Plant-based foods can contain a lot of iron, but it is mainly non-heme iron, which is generally less well absorbed than iron from meat. Therefore, you can have a seemingly good iron intake on paper but still have low iron stores. Official advice for vegetarian diets specifically highlights iron as a nutrient to pay attention to.
The most important marker of the body's iron stores is ferritin. Ferritin shows how large your iron stores are. If ferritin is low, it indicates iron deficiency, even before the blood value has had time to drop. Blood status and hemoglobin are also important, but they can be normal for a long time even though the stores are starting to empty. In cases of suspected iron deficiency, ferritin is therefore often more informative than Hb alone.
Markers that are often relevant:
Ferritin
Blood status with hemoglobin, MCV and MCH
Transferrin saturation or iron/TIBC in some cases
CRP as an aid to interpretation, since ferritin can rise during inflammation and then mask iron deficiency.
This is particularly important for:
women with heavy menstruation
pregnant women
endurance athletes
people with fatigue, palpitations or shortness of breath
people with gastrointestinal problems or impaired absorption
Vitamin D, calcium and sometimes folate – markers for skeletal and general health
Vitamin D is not a typical “vegetarian deficiency” in the same way as B12, but it is still an important marker as many people in northern Europe have low levels, especially during the winter months. Vitamin D is needed for the body to absorb calcium and for normal skeletal and muscle function. The established blood marker is 25-hydroxyvitamin D, often written 25(OH)D.
You may especially consider checking vitamin D if you:
rarely spend time in the sun
have dark skin
cover your skin for cultural or medical reasons
are older
avoid fortified dairy products or fortified herbal drinks
have osteoporosis, muscle weakness or diffuse pain
Calcium is sometimes measured in the blood, but serum calcium does not always reflect the body's calcium intake very well. The body keeps the calcium level in the blood within narrow limits. Therefore, calcium tests are rarely the best screening test for vegetarians without a specific question. It is more important to assess dietary intake, vitamin D status and, if necessary, other markers linked to skeletal metabolism.
Folate is rarely low in vegetarians, since green leafy vegetables, legumes and whole grains often contain a lot of folate. However, in some cases it may still be relevant to measure it, especially in cases of anemia or unclear symptoms. It is important to know that high folate intake can mask the blood picture effects that are otherwise seen in B12 deficiency. Therefore, folate and B12 should often be assessed together if blood status is abnormal.
Iodine, zinc and selenium – often overlooked but sometimes very important
When talking about a vegetarian diet, many focus on B12 and iron, but iodine is a marker that is often forgotten. Iodine is needed for the thyroid gland to be able to form hormones that control metabolism, temperature regulation and energy metabolism. In many dietary patterns, iodine comes primarily from dairy products, fish and shellfish. Those who eat vegetarian food and at the same time avoid dairy or rarely use iodized salt may therefore be at risk of low intake. Systematic reviews also show that vegetarians and especially vegans more often have lower iodine intake and poorer iodine status.
Iodine is, however, difficult to assess with standard blood tests. The test that best reflects intake at a population level is urinary iodine, but in an individual the value can vary from day to day. If you suspect that low iodine intake has affected the thyroid gland, you can also check:
TSH
Free T4
Sometimes Free T3
It is important to understand that these tests do not measure iodine status directly, but they can show whether the thyroid gland is functionally affected.
Zinc may also be relevant, since absorption from plant foods is lower and serum zinc on average tends to be lower in vegetarians and vegans. Symptoms of zinc deficiency are often non-specific, such as decreased appetite, skin problems, poor wound healing and sometimes an impact on the immune system. Serum zinc can be used, but interpretation is not always easy because the level is affected by, among other things, time of day and inflammation. It is therefore a test that should be ordered selectively, not routinely for everyone.
Selenium receives less attention, but may be relevant in very one-sided diets or if you also have questions about thyroid health. The levels in plant foods vary depending on the soil content. This means that intake can differ greatly between different countries and different foods. Selenium is not routinely measured in all vegetarians, but can be considered in special cases.
When should a vegetarian take tests?
You don't have to wait until you feel clearly unwell. On the contrary, the point of a health check is to detect abnormalities early. This is especially true because several deficiencies develop slowly and can cause diffuse symptoms.
It is especially reasonable to get tested if you:
have been a vegetarian for a long time
eat very few eggs and dairy products
are vegan or "almost vegan"
are pregnant, breastfeeding or planning a pregnancy
have heavy periods
feel tired, dizzy, frozen or lack energy
have tingling, numbness or difficulty concentrating
have a gastrointestinal disease, such as celiac disease or inflammatory bowel disease
train hard or have a high energy requirement
want to have a preventive health check-up through your employer or privately
For many vegetarians, a sensible basic panel goes a long way. It may, for example, contain:
active B12and/or MMA if necessary
TSH if low iodine intake or thyroid effects are suspected
The most important thing is that the test results are interpreted in the right context. A value may be “within reference” but still be insufficient for you if you have symptoms, risk factors or a diet with limited sources of certain nutrients.
A vegetarian diet can therefore be both healthy and sustainable, but it does well when followed up with the right markers. Vitamin B12 and ferritin in particular are often central, while vitamin D, iodine-related tests and sometimes zinc or folate may be relevant depending on how you eat and how you feel.
