Vitamins and herbal preparations, particularly those sold in health food stores, are considered by many to be innocuous but may have potential toxicity when taken in excessive amounts over a period of time. Also, herbal preparations may contain toxic contaminants that can cause acute poisoning.
Hypervitaminosis from the fat-soluble vitamins A, D, and E can produce chronic toxicity (after weeks to months of excessive ingestion) or subacute toxicity (after days to a few weeks). Of the water-soluble vitamins, niacin, pyridoxine, and ascorbate are associated with toxicity (Table 205-1).
TABLE 205-1Symptoms of Hypervitaminosis ||Download (.pdf) TABLE 205-1 Symptoms of Hypervitaminosis
|Vitamin ||Symptoms |
|Vitamin A || |
Subacute toxicity: red peeling rash, headache, vomiting
Chronic toxicity: blurred vision, appetite loss, abnormal skin pigmentation, hair loss, dry skin, pruritus, long-bone pain, bone fractures, rare cases of pseudotumor cerebri, hypercalcemia, and hepatic failure
|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 in parenteral form (rare) |
|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, dose >100 milligrams, redness, burning, and itching of the face, neck, and chest; rarely hypotension
Chronic toxicity: doses >2000 milligrams/d, abnormalities of liver function, impaired glucose tolerance, hyperuricemia, skin dryness and discoloration
|Vitamin B6 (pyridoxine) ||Subacute and chronic toxicity: doses >1–3 grams/d orally or more over several weeks, peripheral neuropathy with unstable gait, numbness of the feet, similar symptoms in the hands and arms, 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 usually found in two forms: retinyl palmitate (an ester) from animal sources or carotenoids found in plants. After ingestion, the ester form is hydrolyzed in the gastrointestinal 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. Plants containing the carotenoids have β-carotene, which is the vegeTable compound most efficiently converted to retinol. The liver contains approximately 95% of body vitamin A stores.
Vitamin A forms part of the visual pigments ...