While it is very difficult to ingest too much vitamin B3 or niacin, it is possible to experience a niacin overdose from taking an overabundance of vitamin supplements. Thanks to the fact that vitamin B3 is water-soluble and very little is stored in the body at any one time, the chances of overdosing are relatively low. Unfortunately, when too much niacin is consumed, serious side effects such as dizziness, skin flushing, nausea, and pain in the abdomen may occur. Prolonged overdosing on the nutrient can even lead to hepatoxicity, or permanent damage to the liver.
While skin flushing is relatively common when niacin as nicotinic acid is consumed, the flushing is normally short-lived, but some slight tingling may also occur. This is due to the dilating effect the supplement has on the veins within the body. When an inordinate amount of niacin is consumed, the flushing may be extremely intense, and can be accompanied by dizziness as well as prolonged periods of tingling that turn into itching. Some people have reported that attempting to consume more than one gram of niacin at a time also causes numbness of the lips as well as dizziness and a prolonged period of flushing.
Rapid heartbeat is another common sign of niacin overdose. The change in heart rate may occur along with other symptoms or emerge as the only apparent symptom of the overdose. Of all the outward manifestations of a niacin overdose, this is the one that often causes the highest degree of alarm. Should the increased palpitations continue for more than a short period of time, medical attention should be obtained as quickly as possible.
Pain in the abdominal area may also occur from a niacin overdose, especially if the supplement is taken on an empty stomach. Physicians who prescribe larger doses of niacin as treatment for cholesterol issues sometimes recommend that patients take the niacin during or after a meal, rather than between meals, in order to avoid the potential for cramping and discomfort in the area of the stomach. In some cases, the cramping is accompanied by diarrhea. Fortunately, consuming some type of soft food will often help to calm the stomach pain and counteract the niacin overdose to some degree.
While many of the signs of a niacin overdose are quickly resolved, there is one potential side effect that has a lasting impact. Continued usage of exceptionally high dosages of niacin may result in damage to the liver, known as hepatoxicity. This condition can be treated, but is considered irreversible. While there is no consensus on what constitutes a risk level of niacin consumption, many physicians do not recommend more than three grams per day. In any event, niacin supplements of more than the amounts typically found in multi-vitamins should not be taken without consulting a physician, and that dosage should never exceed the amount determined by the doctor to be safe for the individual patient.
