Vitamin & Mineral Deficiency

Common vitamin and mineral deficiency blood tests

Who is at highest risk of vitamin deficiency?

Vitamin D deficiency: the most prevalent

Vitamin D deficiency affects an estimated 40% of people globally. Risk factors include limited sun exposure, indoor lifestyle, darker skin pigmentation, obesity and living at high latitudes. Levels below 20 ng/mL are considered deficient; below 10 ng/mL is severe deficiency requiring high-dose supplementation. Even people who eat well can be deficient as very few foods naturally contain significant vitamin D.

Vitamin B12 deficiency: often missed

B12 is found almost exclusively in animal products. Deficiency is particularly common in vegetarians, vegans and the elderly. It can take 3–5 years of inadequate intake for deficiency to develop as the body stores significant reserves. Symptoms, fatigue, tingling, memory problems, are often attributed to other causes. Severe B12 deficiency causes irreversible nerve damage if untreated. Metformin (a common diabetes drug) reduces B12 absorption and should be monitored annually.

Folate deficiency in pregnancy

Folate (vitamin B9) deficiency in the first 28 days of pregnancy, before most women know they are pregnant, significantly increases the risk of neural tube defects (spina bifida, anencephaly). All women planning pregnancy or of childbearing age are recommended to take 400 mcg folic acid daily. Women with a history of neural tube defect pregnancy need 5 mg daily.

Questions to ask your doctor

• Should I have a full nutritional panel?
• Do I need B12 injections or will oral supplements work?
• What dose of vitamin D should I take?
• If I am pregnant or planning pregnancy, do I need folic acid?
• Is my fatigue explained by vitamin deficiency?

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Vitamin B12 Deficiency. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK441923

References

Sources cited on this page. PubMed links open the original abstract.

1. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–281. PMID 17634462 · doi:10.1056/NEJMra070553

The key vitamins measured by blood tests

Several vitamins are routinely or specifically measured in clinical practice when deficiency is suspected:

• Vitamin D (25-hydroxyvitamin D): The most commonly measured vitamin in the UK. Deficiency (below 25 nmol/L) causes rickets in children and osteomalacia in adults – painful, weak bones due to failed mineralisation. Insufficiency (25–50 nmol/L) is associated with secondary hyperparathyroidism and increased fracture risk. UK guidelines define sufficiency as above 50 nmol/L throughout the year. Risk groups for deficiency: minimal sun exposure (housebound, covering clothing, dark skin tone), older adults, exclusively breastfed infants. NHS recommends vitamin D supplements for all adults during autumn and winter.
• Vitamin B12 (cobalamin): Deficiency causes megaloblastic anaemia and subacute combined degeneration of the spinal cord – demyelination of posterior and lateral columns causing sensory ataxia, weakness, and cognitive impairment. Sources: meat, fish, dairy, eggs. Strict vegans require supplementation. Absorption requires intrinsic factor (IF) from gastric parietal cells – autoimmune destruction of parietal cells (pernicious anaemia, the most common cause of B12 deficiency in the UK) is detected by anti-intrinsic factor antibodies and anti-parietal cell antibodies. Serum B12 below 200 pg/mL is deficient; methylmalonic acid (MMA) is more sensitive for functional deficiency.
• Folate (folic acid, vitamin B9): Deficiency causes megaloblastic anaemia and, critically, neural tube defects (spina bifida, anencephaly) in early pregnancy. All women planning pregnancy should take 400 µg folic acid daily from before conception through the first 12 weeks. High-dose folic acid (5 mg daily) is recommended for women at higher neural tube defect risk (prior affected pregnancy, coeliac disease, diabetes, on anticonvulsants).
• Vitamin A (retinol): Deficiency causes night blindness (earliest symptom), followed by xerophthalmia (dry eyes, Bitot's spots), and eventually corneal ulceration and blindness. Globally, vitamin A deficiency is the leading cause of preventable childhood blindness. In the UK, deficiency is rare except in fat malabsorption syndromes (Crohn's disease, cystic fibrosis, post-bariatric surgery).

Fat-soluble versus water-soluble vitamins – why storage matters

Vitamins A, D, E, and K are fat-soluble – absorbed with dietary fat, stored in the liver and adipose tissue for months. This means deficiency develops slowly in dietary deprivation but also means toxicity can accumulate with excessive supplementation. Vitamin A toxicity (hypervitaminosis A) causes raised intracranial pressure, liver damage, and teratogenicity – supplements above 3000 µg/day should be avoided in pregnancy. Vitamin D toxicity (above 125 nmol/L) causes hypercalcaemia.

Water-soluble vitamins (B vitamins, vitamin C) are not stored in significant quantities – the body excretes excess in urine. Deficiency develops more rapidly with inadequate intake but toxicity is rare (exception: vitamin B6 – pyridoxine toxicity at high doses causes peripheral neuropathy).