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Chapter 205: Vitamins and Herbals

Michael Levine

INTRODUCTION

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.

VITAMINS

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
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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.

VITAMIN A

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) ...

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