Food Toxicology 2(2+0)

Lesson 16 : Toxicity of Nutrients

Water-Soluble Vitamins

As a group, these vitamins tend to have fewer toxic effects compared with fat-soluble vitamins, mainly because water-soluble vitamins are not retained in the body to the same extent as fat-soluble vitamins. When these vitamins reach urinary threshold levels, the excess is eliminated rapidly in the urine. Thus, discernible harm to the individual can be avoided because of these elimination factors preventing accidental or deliberate ingestion of water-soluble vitamins. Nevertheless, adverse effects associated with excessive intakes of some water-soluble vitamins are being reported with more frequency, which increases the need for more judicious use of supplements and for taking precautions to avoid adverse effects.

1. Niacin
   Nicotinic acid in large doses (100 to 300 mg oral or 20 mg intravenous) can result in vasodilative effects. Symptoms include flushing reaction, cramps, headache, and nausea.

2. Folacin
   The major concern with the use of high levels of folic acid is the masking pernicious anemia resulting from vitamin B12 deficiency. Prolonged masking can delay recognition of the neurological aspects of pernicious anemia arising from vitamin B12 deficiency, which if unnoticed can lead to severe neurological damage. High doses (>15 mg) of folic acid are associated with GI disturbance, irritability, malaise, hyper excitability and disturbed sleep.

3. Vitamin B6 (Pyridoxine)
   Pyridoxal hydrochloride demonstrates oral toxicity at ca. 2 g/kg body weight, or 20 times the therapeutic recommended dose, for peripheral neuritis. Such doses result in convulsive disorder and inhibition of prolactin secretion.