Vitamin Deficiency: Signs, Causes and Treatment

How vitamin deficiencies develop

Vitamins are nutrients the body needs in small amounts but cannot make (or cannot make enough of). There are 13:

• Fat-soluble: A, D, E and K. They need fat and bile for absorption and are stored in the body, so deficiency develops slowly.
• Water-soluble: C and the eight B vitamins (thiamine B1, riboflavin B2, niacin B3, pantothenic acid B5, B6, biotin B7, folate B9 and B12). Most are stored only briefly, except B12, which the liver stores for years.

Deficiency usually builds over months to years, often starting with low stores and no symptoms before signs appear.

Symptoms by vitamin

Common symptoms that overlap

Many deficiencies share non-specific symptoms, which is why testing matters:

• tiredness and low energy
• pale skin and breathlessness on exertion (anemia)
• mouth ulcers, cracked lip corners and a sore, swollen tongue
• tingling, numbness or pins and needles in the hands and feet
• hair thinning and brittle nails
• low mood, irritability and poor concentration
• frequent infections and slow wound healing

Causes and risk factors

Low intake

• vegan and strict vegetarian diets without B12 supplements
• very restricted diets, eating disorders, food insecurity
• older adults with poor appetite or limited access to food
• alcohol use disorder, which also impairs absorption, especially of thiamine and folate

Poor absorption

• Celiac disease and Crohn's disease
• Pernicious anemia, an autoimmune condition that blocks B12 absorption
• Weight-loss surgery, especially gastric bypass
• Pancreatic insufficiency, cystic fibrosis and liver disease (fat-soluble vitamins)
• Removal of part of the stomach or small intestine

Medicines

• Metformin: lowers B12 over years
• Proton pump inhibitors and H2 blockers: lower B12 absorption with long-term use
• Some seizure medicines: lower folate and vitamin D
• Methotrexate: blocks folate
• Isoniazid: lowers B6
• Warfarin acts against vitamin K by design

Higher needs or limited sunlight

• Pregnancy and breastfeeding (folate, iron, vitamin D)
• Infants who are exclusively breastfed (vitamin D) and newborns (vitamin K)
• Darker skin, covering skin, living at high latitudes or being housebound (vitamin D)
• Kidney disease and dialysis

How vitamin deficiency is diagnosed

A doctor will ask about diet, alcohol, medicines, gut symptoms and surgery, and examine your skin, mouth, nerves and eyes. Common tests:

• Complete blood count: large red cells suggest B12 or folate deficiency
• Vitamin B12, with methylmalonic acid if results are borderline
• Folate
• 25-hydroxy vitamin D
• Prothrombin time (INR) for vitamin K
• Specific levels for vitamins A, C, E, thiamine and others when suspected
• Tests for the cause: celiac antibodies, intrinsic factor antibodies for pernicious anemia, iron studies

Routine "vitamin panels" for people with no symptoms or risk factors are not generally recommended.

Treatment

• Supplements: tablets for most deficiencies. Doses depend on the vitamin and severity; follow your doctor's advice or the label for standard supplements.
• Injections: B12 injections for pernicious anemia, severe deficiency or nerve symptoms; IV thiamine for suspected Wernicke encephalopathy; vitamin K injection at birth for newborns.
• Treat the cause: a gluten-free diet for celiac disease, reviewing medicines, and lifelong supplements after weight-loss surgery.
• Diet: a varied diet with vegetables, fruit, whole grains, protein foods and dairy or fortified alternatives.

Prevention

• Vegans: take a B12 supplement or eat B12-fortified foods every day.
• Anyone who could become pregnant: take 400 micrograms of folic acid daily.
• Breastfed babies: vitamin D drops of 400 IU daily from the first days of life.
• People with limited sun exposure: discuss vitamin D supplements, especially in winter.
• Weight-loss surgery patients: lifelong multivitamins and regular blood checks.

Frequently asked questions

What are the most common vitamin deficiencies?

In the US and Europe, vitamin D deficiency is the most common, followed by vitamin B12 and folate deficiencies, especially in older adults, vegans and people with gut problems. Iron deficiency, a mineral rather than a vitamin, is also very common. Vitamin C, A and K deficiencies are less common.

Which vitamin deficiency causes tiredness?

Several can. B12 and folate deficiency cause anemia and tiredness. Vitamin D deficiency can cause fatigue and muscle weakness. Thiamine and vitamin C deficiencies also cause exhaustion. Iron deficiency, though a mineral, is another very common cause. A blood test can identify which one.

How do I test for vitamin deficiency?

Your doctor can order blood tests for specific vitamins based on your symptoms and risk factors, typically B12, folate and vitamin D, along with a complete blood count. Tests for other vitamins are done when there is a specific reason. Home test kits exist but are best interpreted with a doctor.

How long does it take to fix a vitamin deficiency?

It depends on the vitamin and how low it is. Many people feel better within a few weeks of starting supplements. B12 levels improve within weeks, though nerve symptoms can take months to recover. Vitamin D usually takes 2 to 3 months to reach normal levels.

Can a vitamin deficiency cause hair loss?

Yes, sometimes. Deficiencies of vitamin D, B12, folate, biotin and iron have been linked to hair thinning. Biotin deficiency is rare, and biotin supplements do not help hair in people who are not deficient. A doctor can test for the common causes.