ConditionWhole body & general
Vitamin Deficiencies: Risk Groups, Testing and Safe Supplementation
Vitamin deficiencies happen when the body gets or absorbs too little of one or more vitamins. They are uncommon in people eating a varied diet, but specific groups are at much higher risk: vegans (vitamin B12), older adults (B12 and D), pregnant people (folate and D), people with celiac or Crohn's disease, people after weight loss surgery, heavy drinkers (thiamine and folate), and people on medicines such as metformin or long-term acid blockers. Targeted testing and the right supplement dose correct most deficiencies, while megadoses can cause harm.
Also called: Hypovitaminosis, vitamin deficiency, nutritional deficiencies, micronutrient deficiencies
At a glance
- Most common in the US
- Vitamin D, B6, B12 and, in certain groups, folate and thiamine.
- Highest-risk groups
- Vegans, older adults, pregnancy, gut disease, weight loss surgery, alcohol use disorder, certain medicines.
- Testing
- Targeted blood tests for people at risk or with symptoms; broad "vitamin panels" are rarely useful.
- Treatment
- Correct the specific deficiency, treat the cause, then maintain with diet or a regular-dose supplement.
- Caution
- Vitamins A, D, B6 and niacin can be toxic in high doses.
When to get help
Call 911 or go to the ER
- Confusion, unsteady walking and abnormal eye movements in someone who drinks heavily or has been vomiting for weeks (possible Wernicke encephalopathy from thiamine deficiency)
- Heavy or unexplained bleeding, or a newborn who has not had vitamin K and bleeds from the umbilical stump or nose
See a doctor within a day or two
- Numbness, tingling or weakness in the feet or hands that is spreading, or memory problems in someone on a vegan diet, metformin or after stomach surgery
- Severe fatigue, breathlessness and paleness (possible deficiency anemia)
- Bone pain, bowing legs or delayed walking in a child
- Bleeding gums, easy bruising and corkscrew hairs in someone with a very limited diet
Book a routine appointment
- Following a vegan diet without B12 supplements or fortified foods
- More than a year after weight loss surgery without vitamin blood tests
- Long-term use of metformin, acid-reducing medicines or anti-seizure drugs
- Planning pregnancy, to start folic acid
Who is most at risk
| Group | Vitamins most often low | Why |
|---|---|---|
| Vegans and some vegetarians | B12; sometimes D | B12 is found naturally only in animal foods |
| Adults over 65 | B12, D | Less stomach acid to release B12; less skin synthesis of vitamin D; less time outdoors |
| Pregnancy and breastfeeding | Folate, D, sometimes B12 | Higher needs; folate prevents neural tube defects |
| Breastfed infants | D, K (at birth) | Breast milk is low in vitamin D; newborns have low vitamin K stores |
| People with darker skin or little sun | D | Less vitamin D made in the skin |
| Celiac disease, Crohn's disease, chronic pancreatitis, cystic fibrosis | Fat-soluble A, D, E, K; B12, folate | Poor absorption |
| After weight loss surgery | B12, D, thiamine, folate, A, E, K | Bypassed stomach and gut segments; reduced intake |
| Alcohol use disorder | Thiamine (B1), folate, B6, niacin | Poor diet, poor absorption, liver damage |
| Eating disorders, very restrictive diets | Multiple | Low intake |
| Smokers | C | Higher turnover |
For a vitamin-by-vitamin list of symptoms, see vitamin deficiency.
Medicines that can lower vitamin levels
- Metformin: long-term use reduces B12 absorption; the ADA recommends periodic B12 checks.
- Proton pump inhibitors and H2 blockers (acid reducers) used for years: lower B12 absorption.
- Anti-seizure drugs such as phenytoin, carbamazepine and phenobarbital: lower vitamin D and folate.
- Methotrexate and trimethoprim: interfere with folate.
- Isoniazid (for tuberculosis): depletes B6, causing neuropathy unless B6 is given.
- Long-term steroids: affect vitamin D and calcium.
- Orlistat and cholestyramine: reduce absorption of fat-soluble vitamins.
- Nitrous oxide used recreationally: inactivates B12 and can cause spinal cord damage.
Key deficiencies in practice
Vitamin B12
The most important deficiency to catch early, because it can cause permanent nerve damage. Symptoms include fatigue, pale skin, tingling in the feet, unsteadiness, memory problems and a sore tongue. Causes include pernicious anemia (an autoimmune condition), vegan diets, metformin and stomach surgery. See vitamin B12 deficiency.
Vitamin D
Very common, particularly in winter at northern latitudes. Severe deficiency causes rickets in children and osteomalacia (soft bones, bone pain, muscle weakness) in adults. See vitamin D deficiency.
Folate
Low folate causes anemia, and in early pregnancy raises the risk of neural tube defects. Anyone who could become pregnant is advised to take 400 micrograms of folic acid daily. See folate deficiency.
Thiamine (vitamin B1)
Mainly seen in heavy drinkers, after weight loss surgery and with prolonged vomiting. It can cause Wernicke encephalopathy and heart failure (beriberi) and needs urgent treatment.
Vitamin C
Rare in the US, but still seen with very limited diets, alcohol use disorder and in some older adults living alone. It causes scurvy: bleeding gums, bruising, poor wound healing and joint pain.
Should you get tested?
Testing is most useful when you have symptoms or are in a risk group. Doctors usually order specific tests rather than a broad panel:
- B12: serum B12, plus methylmalonic acid (MMA) if borderline
- Vitamin D: 25-hydroxyvitamin D
- Folate: serum or red cell folate
- Full blood count: large red cells suggest B12 or folate deficiency
- Vitamin A, E, K, thiamine: in malabsorption, after surgery or with specific symptoms; vitamin K status is checked with a clotting test (PT/INR)
Routine vitamin D screening of healthy adults without risk factors is not recommended by the USPSTF.
Treatment
- Correct the deficiency: higher-dose supplements for a set period, or injections when absorption is poor (for example B12 injections in pernicious anemia, or after gastric bypass).
- Treat the cause: a gluten-free diet for celiac disease, alcohol treatment, medicine review.
- Maintain: a varied diet, fortified foods, and long-term supplements where the risk continues, such as lifelong B12 for vegans and lifelong multivitamins, B12, calcium and vitamin D after bariatric surgery.
- Recheck: blood tests after a few months confirm correction.
Supplement safety
More is not better. Fat-soluble vitamins are stored in the body and can build up.
| Vitamin | Risk with excess |
|---|---|
| A | Liver damage, headaches, bone loss; birth defects in pregnancy (avoid high-dose retinol) |
| D | High calcium, kidney stones, confusion; usually only with very large doses for months |
| B6 | Nerve damage (numbness, tingling) with long-term high doses, including from combined supplements |
| Niacin (B3) | Flushing, liver injury at high doses |
| E | Bleeding risk, especially with blood thinners |
| Folic acid | High doses can mask B12 deficiency |
Tell your doctor about all supplements, as some interact with medicines (vitamin K with warfarin, for example). For most healthy adults eating a varied diet, the USPSTF found insufficient evidence that multivitamins prevent heart disease or cancer, and recommends against beta-carotene and vitamin E supplements for that purpose.
Prevention
- Eat a varied diet with vegetables, fruit, whole grains, legumes, dairy or fortified alternatives, eggs, fish or meat.
- Vegans: take a B12 supplement or eat B12-fortified foods every day.
- Babies: follow pediatric advice on vitamin K at birth and vitamin D drops for breastfed infants.
- Pregnancy: start folic acid before conception.
- After bariatric surgery: take prescribed supplements for life and attend blood test follow-ups.
Frequently asked questions
Who is most likely to have a vitamin deficiency?
People most at risk include vegans, adults over 65, pregnant people, those with celiac or Crohn's disease, people after weight loss surgery, heavy drinkers, people with eating disorders, and those taking metformin, acid-reducing medicines or certain anti-seizure drugs for a long time.
Can medications cause vitamin deficiencies?
Yes. Metformin and long-term acid blockers lower B12; some anti-seizure drugs lower vitamin D and folate; methotrexate affects folate; isoniazid depletes B6. If you take these long term, ask whether periodic blood tests or supplements are recommended.
Should I take a multivitamin?
A multivitamin is reasonable for people with a restricted diet, older adults with poor appetite, or after weight loss surgery. For healthy adults eating a varied diet, evidence does not show that multivitamins prevent heart disease or cancer. Targeted supplements for a confirmed deficiency work better.
Can you take too many vitamins?
Yes. High doses of vitamins A, D, E, B6 and niacin can cause harm, ranging from nerve damage to liver injury and high calcium. Stick to recommended doses unless a doctor prescribes more for a confirmed deficiency, and count vitamins in all products you take.
Which vitamin deficiencies are common in vegans?
Vitamin B12 deficiency is the main risk, because it is found naturally only in animal foods. Vegans may also be low in vitamin D, iodine, calcium, iron, zinc and omega-3 fats. A daily B12 supplement or fortified foods is essential.
Sources
This guide was written from current patient and clinical guidance, including:
- NIH Office of Dietary Supplements: Vitamin and mineral fact sheets
- CDC: Second National Report on Biochemical Indicators of Diet and Nutrition
- American Society for Metabolic and Bariatric Surgery: Integrated health nutritional guidelines for the surgical weight loss patient
- US Preventive Services Task Force: Vitamin, mineral and multivitamin supplementation to prevent cardiovascular disease and cancer
- MedlinePlus: Vitamins