Vegetarian Blood Test: Essential Nutrients to Check

Vegetarianism in the UK has grown significantly — the Food Standards Agency estimates that approximately 3–4% of the UK population identifies as vegetarian, with a further 8–10% as flexitarian. A well-planned vegetarian diet can meet all nutritional requirements, but the emphasis is on "well-planned." Certain nutrients are inherently harder to obtain from a lacto-ovo vegetarian diet, and deficiencies can develop gradually over months or years without obvious symptoms until they become clinically significant.

The good news is that vegetarians are at considerably lower risk of nutrient deficiency than vegans — dairy and eggs provide meaningful amounts of B12, complete protein, calcium, iodine, and some bioavailable iron. But "lower risk" isn't "no risk," and the specific nutrients that need monitoring are well-established.

Vitamin B12: Dairy and Eggs Help — But Often Not Enough

B12 is produced exclusively by bacteria and is found naturally in animal-derived foods. Lacto-ovo vegetarians obtain B12 from eggs, milk, cheese, and yoghurt — which provides a meaningful dietary source that vegans lack entirely. However, studies consistently show that vegetarians still have lower B12 levels than omnivores.

A systematic review published in the European Journal of Clinical Nutrition found that approximately 11% of lacto-ovo vegetarians are B12-deficient (serum B12 below 200 pg/mL), compared to 62% of vegans and 5% of omnivores. The deficiency rate rises with duration of vegetarianism — someone who has been vegetarian for 10+ years is at greater risk than a recent convert.

The amount of B12 in dairy and eggs varies considerably. One large egg provides approximately 0.6 µg of B12 (the daily recommended intake is 1.5 µg in the UK). A 200 ml glass of milk provides approximately 0.9 µg. To meet requirements from these sources alone, you'd need at least two eggs and a glass of milk daily — which many vegetarians don't consistently consume, particularly those who lean towards a plant-heavy diet with occasional dairy.

B12 deficiency develops slowly because the liver stores 2–5 years' worth. By the time serum B12 drops below the reference range, stores are already substantially depleted. Testing annually — and treating any level below 300 pg/mL with a supplement — prevents the neurological damage (peripheral neuropathy, cognitive decline) that can result from prolonged deficiency.

Iron: Absorption Is the Challenge

Vegetarian diets can contain adequate total iron — legumes, fortified cereals, tofu, dark leafy greens, and dried fruits all contribute. The issue is bioavailability. Plant-based iron (non-haem iron) is absorbed at 2–20% efficiency, compared to 15–35% for haem iron from meat. Phytates in wholegrains and legumes, polyphenols in tea and coffee, and calcium in dairy all inhibit non-haem iron absorption further.

The result is that vegetarians are at approximately 1.5–1.8 times higher risk of iron deficiency than omnivores, despite often consuming similar or even higher total dietary iron. Women of childbearing age are at particular risk due to menstrual losses — iron deficiency affects an estimated 20–25% of premenopausal women in the UK overall, and the rate is higher among vegetarians.

Ferritin is the critical test. Serum ferritin below 30 µg/L indicates depleted stores, even if haemoglobin is still normal. Below 15 µg/L is frank deficiency. Vegetarians should aim for ferritin above 40 µg/L as a comfortable buffer. Practical strategies to improve absorption include pairing iron-rich foods with vitamin C (bell peppers, citrus, berries), avoiding tea and coffee within an hour of iron-rich meals, and soaking and sprouting legumes to reduce phytate content.

Zinc: The Overlooked Mineral

Zinc absorption faces similar challenges to iron — phytates in plant foods chelate zinc and reduce bioavailability by 35–45%. The richest dietary sources of zinc are oysters and red meat, neither of which features in a vegetarian diet. Cheese, eggs, legumes, nuts, and seeds provide zinc, but the phytate-to-zinc ratio in plant foods means that the recommended zinc intake for vegetarians may need to be 50% higher than for omnivores to achieve the same absorbed amount.

Zinc deficiency causes impaired immune function (frequent colds and infections), slow wound healing, hair loss, skin problems, and reduced taste and smell. Serum zinc is an imperfect marker — it reflects recent intake rather than stores — but it's the best available clinical test. Levels below 10 µmol/L suggest deficiency.

Approximately 10–15% of vegetarians in developed countries have suboptimal zinc status, though frank clinical deficiency is uncommon in those eating a varied diet with regular legume and nut consumption.

Vitamin D: Not a Vegetarian-Specific Issue, But Still Critical

Vitamin D deficiency affects the UK population broadly — an estimated 40% of adults have levels below 50 nmol/L during winter. For vegetarians, dietary sources are limited: eggs (specifically yolks) provide some vitamin D, and fortified dairy products contribute, but the amounts are modest. Fatty fish is the richest dietary source of vitamin D, which is obviously excluded from a vegetarian diet (unless you're pescatarian).

Mushrooms exposed to UV light provide vitamin D2 (ergocalciferol), but this is less efficiently converted to the active form than vitamin D3 (cholecalciferol) from animal sources. Supplementation with D3 — now widely available in vegetarian-friendly forms derived from lichen rather than lanolin — is recommended for most UK adults from October to March, and year-round for those with limited sun exposure.

Testing vitamin D annually, ideally in late winter when levels are lowest, establishes your baseline and determines whether supplementation dose is adequate. Target level: above 75 nmol/L for optimal health.

Omega-3 Fatty Acids: The Conversion Problem

While not measured on a standard blood test, omega-3 status is a relevant consideration for vegetarians. The long-chain omega-3s EPA and DHA — critical for brain function, cardiovascular health, and inflammation regulation — are found primarily in oily fish. The plant-based precursor ALA (from flaxseed, chia seeds, walnuts) can be converted to EPA and DHA, but conversion rates are extremely low: approximately 5–10% for EPA and less than 1% for DHA.

Pescatarian vegetarians who eat fish 2–3 times per week generally have adequate omega-3 status. Lacto-ovo vegetarians who don't eat fish should consider an algae-derived omega-3 supplement providing at least 250 mg of combined EPA and DHA daily.

Calcium and Iodine: Where Dairy Helps

Calcium is one area where lacto-ovo vegetarians have a clear advantage over vegans. Dairy is an excellent, bioavailable calcium source — a 200 ml glass of milk provides approximately 240 mg of calcium (the adult UK RNI is 700 mg). Vegetarians who consume dairy regularly generally meet calcium requirements without difficulty.

Iodine is primarily obtained from dairy products and fish in the UK diet. Milk is actually the most significant iodine source for most UK adults — 200 ml provides approximately 50–100 µg (the adult RNI is 140 µg). Vegetarians who consume dairy regularly are generally iodine-sufficient, but those who limit dairy should be aware of this gap. Iodine deficiency during pregnancy is particularly concerning as it impairs foetal brain development.

Full Blood Count: The Baseline Check

The full blood count provides haemoglobin (overall anaemia detection), MCV (distinguishes iron deficiency from B12/folate deficiency), and other red cell indices. For vegetarians, it's the first-line test that determines whether further investigation is needed. A low MCV (below 80 fL) with low ferritin confirms iron-deficiency anaemia. A high MCV (above 100 fL) with low B12 or folate suggests megaloblastic anaemia.

How Often Should Vegetarians Test?

Annual testing is sensible for established vegetarians. New vegetarians should test at baseline (before or shortly after switching) and again at 6–12 months to catch early trends. Pregnant or breastfeeding vegetarians should test more frequently — every trimester during pregnancy at minimum.

Recommended Blood Tests for Vegetarians

The Blood Health 6 biomarker test (£89) provides the focused iron panel (ferritin, serum iron, TIBC, transferrin saturation) plus full blood count — ideal for monitoring the most common deficiency in vegetarians. It's a practical, targeted choice for annual iron surveillance.

For comprehensive nutritional monitoring covering B12, folate, vitamin D, iron studies, full blood count, thyroid function, and liver and kidney health, the Core Health 45 biomarker test (£120) provides broader coverage in a single panel. It's the better choice for vegetarians who want a complete annual health check rather than just iron monitoring.

A vegetarian diet offers well-documented health benefits — lower cardiovascular risk, reduced cancer incidence, and lower rates of type 2 diabetes. But these benefits are maximised when nutritional gaps are identified and addressed rather than allowed to develop silently. Annual blood testing takes the guesswork out of vegetarian nutrition and ensures you're getting the benefits of the diet without the avoidable risks.