Niacin excess/toxicity

The effects of most vitamin B overdoses have not been documented, although large dosages of pyridoxine have been reported to cause peripheral neuropathies. Ataxia and numbness of the hands and feet and impairment of the senses of pain, touch, and temperature may result. Excessive niacin intake may result in flushing, pruritus, and gastrointestinal disturbances. These symptoms are due to niacin s ability to cause the release of histamine. Large dosages of niacin can result in hepatic toxicity. 

Abnormal accumulation in tissues and overloading of normal metabolic pathways, leading to signs of toxicity and possibly irreversible lesions. Niacin (Section 8.7.1), and vitamins A (Section 2.5.1), D (Section 3.6.1), and Bg (Section 9.6.4) are all known to be toxic in excess (see Section 1.2.4.3 for a discussion of tolerable upper levels of intake). 

Acute ingestions seldom require treatment. Reassurance that the niacin flush will gradually resolve over the next couple of hours should be given. In cases of chronic excessive use, the patient should be instructed to discontinue the supplement. Any toxic symptoms should be treated symptomatically. 

Niacin is a safe drug to use and its toxicity is dose related. Niacin toxicity has been shown to manifest itself as altered mental status, nausea and vomiting (Mittal et al. 2007). Evidence shows that excess niacin can cause hepatic dysfunction with associated coagulopathy, jaundice and fulminant liver failure (Etchason et al. 1991 Fischer et al. 1991). In addition niacin overdose can cause impaired glucose control (Mittal et al. 2007). 

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