Vegan Diet: What to Check in Your Blood Tests

Why is blood testing important for vegetarians and vegans?

A plant-based diet can be complete and healthy, but some nutrients are harder or impossible to obtain from plants alone. Deficiencies often develop gradually -- over months or years -- and symptoms may only appear when the deficit is already significant and potentially harmful to health.

Regular blood tests help detect deficiencies at an early stage, when they are easy to correct with dietary changes or supplements. This is especially important for vegans who completely avoid animal products, but also relevant for lacto-ovo vegetarians and people who simply eat little meat.

It is important to understand that a plant-based diet is not inherently deficient -- it simply requires more attention to certain nutrients. Knowing what to check provides peace of mind and control.

Vitamin B12 -- the most important marker

Vitamin B12 (cobalamin) is naturally found only in animal products: meat, fish, eggs, and dairy. Plant sources (fermented products, spirulina, algae) do not provide reliable and biologically active B12 -- the B12 form they contain is often inactive and may even interfere with true B12 absorption.

The body's B12 reserves in the liver can last 2-5 years, so deficiency does not manifest immediately. However, when symptoms appear -- tingling in fingertips, memory problems, fatigue, balance disorders -- nerve damage may already be partial and not always fully reversible (Source -- Pawlak, 2016).

Recommended testing: B12 levels in blood (normal is usually above 200 pg/mL), and if in doubt -- holotranscobalamin or methylmalonic acid, which are more sensitive and earlier indicators. Blood B12 may appear normal even though a functional deficiency already exists.

Iron and ferritin

Plant-based iron (non-heme) is absorbed less efficiently than animal-based (heme) iron -- 2-20% compared to 15-35%. This means vegetarians need to consume about 1.8 times more iron than meat eaters to meet their needs (Source -- Saunders, 2014).

Ferritin is the primary indicator of iron stores. Its decline signals the onset of deficiency even before anemia develops. Ferritin below 30 ng/mL already indicates declining stores, even though hemoglobin may still be within normal range. This means ferritin is an earlier and more sensitive signal than hemoglobin.

Vitamin C increases non-heme iron absorption by 3-6 times. Therefore, it is beneficial to consume vitamin C sources -- citrus fruits, bell peppers, tomatoes -- alongside iron-rich foods (lentils, spinach, tofu, whole grain products). Meanwhile, tea, coffee, and calcium can reduce iron absorption, so they are best consumed separately from iron-rich meals.

Vitamin D and calcium

Vitamin D is important for calcium absorption, immune function, muscle function, and mood. Its primary source is sunlight, but at northern latitudes (Lithuania -- 54-56 degrees latitude), from October to March, vitamin D production in the skin virtually stops due to the low sun angle.

Vegans who do not consume dairy products get less calcium and vitamin D from food. Studies show that vegans' vitamin D levels are on average 34% lower than those following a mixed diet (Source -- Chan, 2011). Calcium sources for vegans: fortified plant milk alternatives, calcium-set tofu, sesame seeds, broccoli, kale.

It is recommended to check 25(OH)D blood levels once a year, ideally in spring after the winter period. The optimal level is above 30 ng/mL (75 nmol/L). If deficient, discuss supplementation with your doctor -- the dose depends on current levels.

Zinc, folate, and other markers

Zinc is important for immune function, wound healing, protein synthesis, and skin health. Plant sources contain zinc (seeds, nuts, legumes, whole grain products), but phytates -- compounds naturally present in plants -- reduce its absorption. Soaking, sprouting, and fermenting help reduce phytate content and improve zinc bioavailability.

Vegetarians typically get enough folic acid (folate), as it is abundant in leafy vegetables, legumes, and citrus fruits. However, it is worth testing, especially for women planning pregnancy, as folate deficiency in the first weeks of pregnancy can have serious consequences for fetal development.

Omega-3 fatty acids (EPA and DHA) are another marker that vegans may get less of, as their primary source is fatty fish. Plant sources (flaxseeds, chia, walnuts) provide the ALA form, whose conversion to EPA and DHA is limited -- about 5-10%.

Practical testing plan

1. Every 6-12 months, check: B12, ferritin, iron, hemoglobin levels -- this is the core panel. 2. Once a year: vitamin D (especially in spring, after winter), calcium, zinc. 3. Additionally: complete blood count (CBC), which helps detect anemia and other changes. 4. If you feel well -- test proactively, as many deficiencies are asymptomatic at an early stage. If fatigue, hair loss, or tingling occurs -- get tested sooner. 5. Discuss all results with your doctor or dietitian, who can help create an individualized nutrition plan.

When to act immediately

See a doctor urgently if you notice: persistent tingling or numbness in hands or feet, severe fatigue that does not resolve with rest, shortness of breath with light physical exertion, balance disorders or unusual weakness, unusually pale skin, tongue pain or mouth sores. These symptoms may indicate significant B12 or iron deficiency that requires immediate correction.

This is not medical advice. Consult your doctor for health decisions.