The recommended dose of niacin for men is 16 milligrams per day, while most women need 14, according to WebMD. Pregnant women require 18 milligrams, and breastfeeding mothers should get 17. Children's requirements vary by age, and range between 2 and 16 milligrams.
The upper limit of niacin for most adults is 35 milligrams a day, recommends WebMD. However, doctors sometimes prescribe 2 to 3 grams to patients with high cholesterol. When niacin, or vitamin B, is used as a supplement, its typical side effects are flushing, nausea and diarrhea. If niacin is taken regularly, the side effects gradually disappear. Foods that naturally contain niacin are leafy vegetables, meat, poultry, fish and eggs.