Niacin promotes insulin resistance et reduces glucose tolerance in a dose-dependent manner. Pour personnes without diabetes, blood glucose levels generally remain within normal limits. Diabetics should limit their quotidien niacin intake à a maximum de 1.5 grams à minimize effets on blood glucose levels.
Niacin in doses above 50 mg may cause a 'niacin flush' avec redness de le face, arms, et chest (sometimes accompanied by slight swelling de le skin), a burning, tingling, et/ou itching sensation, et sometimes a headache. Ces effets usually last between 30 minutes et an hour. Ce reaction est intense but harmless et temporary. Cela est pas an allergic reaction. Le flush pouvez be limited by gradually increasing le dose et combining niacin avec a B-complex vitamin et vitamin C.
High doses de niacin (greater than 3 grams per jour) may be toxic à le liver, leading à elevated liver function tests et jaundice, et pouvez cause gastrointestinal issues such as nausea, vomiting, acide reflux, loss de appetite, bloating, diarrhea, et peptic ulcers. Niacin may also worsen allergic reactions by stimulating le release de histamine.
A dose de niacin de 1000 mg per jour may significantly increase homocysteine levels. Ce increase pouvez be prevented by also supplementing avec vitamin B6.