Since the 1940s, the U.S. Code of Federal Regulations, 137.165 (a), has recommended that each pound of food made from flour should contain 24 milligrams of niacin to help prevent vitamin B3 deficiency. For years, some doctors have prescribed niacin to treat people with low blood levels of the good HDL cholesterol. (Low levels of HDL are associated with increased risk for heart attacks). However, a new study from a highly-respected group of researchers at the Cleveland Clinic found that high doses of niacin may increase risk for arteriosclerosis, heart attacks and strokes (Nature Medicine, Feb 19, 2024;30:424–434). These results help to explain why two large niacin studies (HPS2-THRIVE and AIM-HIGH), found that prescribing niacin to people who had low-blood levels of the good HDL cholesterol increased their risk for heart attacks, even though niacin increased blood levels of the good HDL cholesterol.
High doses of vitamin B3 (niacin) increase blood levels of pro-inflammatory molecules called 4PY and 2PY. 4PY has directly been shown to cause blood vessel damage and plaque formation in arteries.
The Study
Researchers followed 1,162 patients without heart disease for three years and found high levels of niacin in 25 pecent of them. Those with high niacin levels had twice the risk of suffering a heart attack, compared to those with normal levels. Those with high niacin levels had a risk for a heart attack that was as high as for those with diabetes or a previous heart attack. Increased doses of niacin were associated with increased blood levels of the breakdown products of excess niacin called 2PY and 4PY, both of which are associated with increased risk for blood markers of inflammation and suffering a heart attack. Giving 4PY to mice markedly increased several blood markers for increased heart attack risk.
Regulations on Adding Niacin to Flour Will Be Kept
We still need regulations to have niacin in foods made from flour, but future studies may recommend reducing the amounts. Before we had these regulations, the wheat germ was removed from flour to prolong its shelf life, and niacin deficiency, called pellagra, was common. Symptoms of pellagra include mental confusion, diarrhea, muscle weakness, loss of appetite, belly pain, inflamed mucus membranes and skin sores. Pellagra is now virtually never seen in North America.
My Recommendations
The average North American adult takes in three times the recommended dietary allowance of niacin.
• It appears to be safe to take an ordinary one-a-day multiple vitamin pill if you wish. However, this study and others suggest that you should consult your doctor before you consider taking high-dose over-the-counter niacin supplements that are popular because of claims of their anti-aging effects. Common anti-aging supplements may contain high doses of niacin that may increase your risk for heart attacks and strokes.
• You can get plenty of niacin from a diet that includes whole grains, fruits and vegetables. I recommend that you also restrict sugar-added foods and drinks.
