Vitamins and herbal preparations, particularly those sold in health food stores, are considered by many to be innocuous but may have potential toxicity, especially when taken in excessive amounts over a period of time. Also, herbal preparations may contain toxic contaminants that can cause poisoning.
Hypervitaminosis from the fat-soluble vitamins A, D, E, and K can produce subacute toxicity (after days to a few weeks) or chronic toxicity (after weeks to months of excessive ingestion). Of the water-soluble vitamins, niacin, pyridoxine, and ascorbate are associated with toxicity (Table 205-1).
TABLE 205-1Clinical Features of Hypervitaminosis ||Download (.pdf) TABLE 205-1 Clinical Features of Hypervitaminosis
|Vitamin ||Symptoms |
|Vitamin A || |
Subacute toxicity: red peeling rash, headache, and vomiting.
Chronic toxicity: blurred vision, appetite loss, abnormal skin pigmentation, hair loss, dry skin, pruritus, long-bone pain, bone fractures, liver failure, pseudotumor cerebri, and hypercalcemia.
|Vitamin D ||Subacute toxicity: hypercalcemia, anorexia, nausea, abdominal pain, lethargy, weight loss, polyuria, constipation, confusion, and coma. |
|Vitamin E ||Chronic toxicity: coagulopathy in patients on warfarin, nausea, fatigue, headache, weakness, and blurred vision. |
|Vitamin K ||Acute toxicity: anaphylactoid reactions if given rapidly in the parenteral form (rare). Interferes with warfarin, resulting in subtherapeutic coagulation. |
|Vitamin B1 (thiamine) ||No toxicity observed with ingestion of large doses. |
|Vitamin B2 (riboflavin) ||No toxicity observed with ingestion of large doses. |
|Vitamin B3 (niacin) || |
Acute toxicity: “niacin flush” (redness, burning, and itching of the face, neck, and chest). Hypotension a rare possibility.
Chronic toxicity: Abnormalities of liver function, impaired glucose tolerance, hyperuricemia, skin dryness, and discoloration.
|Vitamin B6 (pyridoxine) ||Subacute and chronic toxicity: peripheral neuropathy with unstable gait, and marked loss of position and vibration senses. |
|Vitamin B12 ||No toxicity observed with ingestion of large doses. With large IV doses: erythema of skin, mucous membranes, serum, and urine. Rare anaphylactoid reactions. Possible interference with serum colorimetric lab studies. |
|Folate ||No toxicity observed with ingestion of large doses. Masking of macrocytic anemia from vitamin B12 deficiency with large doses of folate. |
|Vitamin C (ascorbate) ||Chronic toxicity: nephrolithiasis (controversial), intrarenal deposition of oxalate crystals with renal failure; large doses can produce diarrhea and abdominal cramps. |
Dietary vitamin A is present in two forms: preformed vitamin A (retinol and retinyl palmitate [an ester] from animal sources) and provitamin A (carotenoids) found in plants. After ingestion, the ester form is hydrolyzed in the GI tract to retinol. Retinol is then absorbed into intestinal mucosal cells, where it then combines with a fatty acid to again become a retinyl ester. Carotenoids are dark-colored compounds found in plants. β-Carotene is the carotenoid most efficiently converted to retinol by duodenal mucosal cells. The recommended daily allowance (RDA) for preformed vitamin A (retinol) is 900 micrograms (3000 IU) for adolescents and adult men, and 700 micrograms (2400 IU) ...