Deficiency symptoms

What are the symptoms of vitamin deficiency?

Overt vitamin deficiencies present with vitamin-specific disease pictures. According to the Merck Manual’s table, these are: night blindness, xerophthalmia, and keratomalacia in vitamin A deficiency; scurvy (bleeding, loose teeth, gum inflammation, bone defects) in vitamin C deficiency; beriberi (peripheral neuropathy, heart failure) and Wernicke-Korsakoff syndrome in B1 deficiency; pellagra (dermatitis, glossitis, digestive and central nervous system disorders) in niacin deficiency; rickets and osteomalacia in vitamin D deficiency; megaloblastic anemia in B12 and folate deficiency; and bleeding in vitamin K deficiency. ^[1]

In mild or moderate deficiency, however, the picture is much less clear. The map below summarizes which vitamins and minerals commonly heard complaints may be related to and the limits of that relationship; in each row the details are on the relevant subpage.

The table is not a diagnostic tool: the reason more than one vitamin or mineral is listed against a complaint is that the same symptom has more than one origin.

Deficiency of which vitamin causes fatigue?

Fatigue is the most frequently cited symptom of vitamin deficiency and the least specific. The systematic review by Houston and colleagues examined iron supplementation in adults without anemia but with iron deficiency: 18 studies (1,170 patients) were included from 11,580 records; iron reduced self-reported fatigue (standardized mean difference −0.38; 4 studies, 714 people), but there was no difference in objective measures of physical capacity such as maximal oxygen consumption. ^[2] That is, benefit for reported fatigue may be obtained in iron deficiency, but this is not proof that the fatigue was caused by iron deficiency.

The guideline by Devalia and colleagues points to a similar issue for B12: in determining the meaning of test results assessing cobalamin status, the clinical picture is the most important factor, because there is no gold standard test that defines deficiency. ^[4]

Is hair loss from vitamin deficiency?

According to the review by Almohanna and colleagues, vitamins and minerals play a role in the hair follicle cycle, but exactly what that role is remains unclear; it is stated that deficiencies may be a modifiable risk factor, but that large placebo-controlled studies are needed to determine the effect of supplementation on hair growth. According to the review, biotin deficiency causes hair loss, but there is no evidence that biotin supplementation increases hair growth; in addition, externally taken biotin can distort some laboratory tests. For zinc, the data are not homogeneous and zinc screening is not recommended; excess vitamin A causes hair loss. For iron, the relationship between low ferritin and hair loss has been debated for years, and there is no agreed threshold for “normal ferritin.” ^[3]

Does a muscle cramp mean magnesium deficiency?

No. The Cochrane review by Garrison and colleagues (11 studies, 735 people) examined the effect of magnesium on skeletal muscle cramps. In idiopathic (unknown cause) cramps, the difference between magnesium and placebo was small and not statistically significant; the participants of these studies were mostly older adults (mean age 61.6–69.3) and the most common presentation was nocturnal leg cramps. The difference in weekly cramp count was −0.18 cramps/week (95% CI −0.84 to 0.49) in 5 studies (307 people) and was assessed as moderate-certainty evidence; all studies of pregnancy-associated leg cramps were found to have a high risk of bias. ^[6] In low calcium (hypocalcemia), on the other hand, paresthesias, muscle spasms, cramps, and tetany are the most common symptoms; this means that low calcium can cause cramps, but not every cramp is due to calcium or magnesium deficiency. ^[8]

Why are symptoms not specific, and why does self-diagnosis mislead?

For three reasons:

1. The same symptom comes from many origins. Fatigue, numbness, cramps, hair loss, and cracks at the corners of the mouth are associated with more than one vitamin and mineral. In the Merck Manual’s table, the same finding (for example, neuropathy or anemia) appears against several vitamins. ^[1]
2. Mild deficiency often causes no symptoms. For deficiency to turn into a disease picture, the vitamin’s stores must be depleted; the Merck Manual reports that this takes weeks to months for water-soluble vitamins (except B12) and more than a year for fat-soluble vitamins and B12. ^[1] Vitamin K falls outside this generalization: according to the NIH, its store is relatively small; vitamin K deficiency bleeding can be seen in newborns in the first weeks, whereas in adults clinical deficiency is very rare and is usually associated with malabsorption or medicines that affect vitamin K metabolism. ^[9]
3. A reduction in a subjective complaint alone does not prove the cause. In iron studies, only self-reported fatigue changed, and objective physical capacity did not. ^[2]

B6 is a good example of this confusion: B6 deficiency causes neuropathy, and excess intake also causes neuropathy. The Merck Manual lists seizures, anemia, neuropathy, and seborrheic dermatitis among the findings of B6 deficiency, and peripheral neuropathy as the finding of its toxicity. ^[1] Whether a complaint of neuropathy comes from B6 deficiency or from excess intake therefore requires a separate evaluation.

Who is at higher risk of vitamin deficiency?

According to the Merck Manual, in countries with a low rate of food insecurity, vitamin deficiencies are mostly associated with the following: poverty, extremely restricted or fad diets, medicines and drug-nutrient interactions, alcohol use disorder, long-term and inadequately supplemented parenteral nutrition, and malabsorption disorders. Mild vitamin deficiency is common in frail and institutionalized older adults with protein-energy malnutrition. ^[1] The full list of risk groups in the Turkish Ministry of Health’s TÜBER (Türkiye Dietary Guidelines) 2022 guide is on the What are vitamins? page.

For some deficiencies the risk group is more distinct: B1 deficiency stands out in alcohol use disorder and bariatric surgery, iron deficiency in heavy menstrual bleeding and pregnancy, and B12 deficiency in absorption problems; details are given on the subpages.

Which tests are meaningful?

The meaning of a test varies by vitamin; therefore, rather than “measuring everything,” a test appropriate to the complaint and risk status is chosen.

• Iron: The British Society of Gastroenterology guideline recommends iron tests to prove iron deficiency; it describes serum ferritin as the single most useful marker for iron deficiency anemia and states that when falsely normal ferritin is suspected, tests such as transferrin saturation can help. ^[7] The same guideline reports that iron deficiency anemia can reflect a serious gastrointestinal disease; for the initial investigation of confirmed iron deficiency anemia, it recommends urinalysis or urine microscopy, celiac disease screening, and, in appropriate cases, endoscopic examination of the upper and lower gastrointestinal tract. ^[7]
• B12 and folate: According to the British Committee for Standards in Haematology guideline, the first-line test for B12 is serum cobalamin; when uncertain, as a second-line test, plasma methylmalonic acid (MMA) and, although less specific, homocysteine can be useful. According to the guideline, exact threshold values cannot be determined and local reference ranges should be established. It is stated that if there is a discrepancy between the test result and strong clinical findings of deficiency, treatment should not be delayed in order to prevent neurological damage. For folate, serum folate is the first-line test and has equivalent diagnostic power to red cell folate. ^[4]
• Vitamin D: The Endocrine Society 2024 guideline does not recommend routine 25(OH)D testing for disease prevention in people without an established indication for 25(OH)D testing or vitamin D treatment (“suggests against” in the guideline’s wording, that is, a conditional recommendation). As the rationale, it cites the absence of clinical trial evidence supporting routine screening in the general population, in people with obesity, and in dark-skinned people, and the absence of clear evidence defining the optimal 25(OH)D target for disease prevention. ^[5]
• Calcium: Before a diagnosis of hypocalcemia, serum calcium is corrected for albumin level; hypocalcemia is spoken of when corrected total calcium is below 2.12 mmol/L. ^[8]
• Magnesium, zinc, potassium, vitamin A, and iodine: For these minerals and vitamins, the interpretation of the test has separate sources; blood level does not always reflect the status in tissues. Details are on the relevant subpages: magnesium, zinc, potassium, vitamin A, iodine.

When is physician evaluation needed?

Some pictures require urgent evaluation; in these, starting a supplement at home and waiting is not an appropriate path. B1 deficiency that can progress to Wernicke encephalopathy, B12 deficiency with marked neurological findings (confusion, paresthesia, ataxia ^[1]), and low potassium and calcium that affect heart rhythm or seizure threshold belong to this group; details are given on the subpages. In iron deficiency anemia, too, investigating the cause is as important as the treatment itself. ^[7]

This guide does not diagnose and does not recommend personal doses. Instead of starting a supplement based on a single symptom, the duration of the symptom, accompanying findings, and risk factors are evaluated with a physician.