One thing that this reviewer has learned over many decades as a registered dietitian and nutrition research specialist is that the nutrition field has always been prone to diets, fads, and what might be called irrational exuberance about the claimed health benefits of a wide variety of food supplements.
Some of you may recall when Linus Pauling’s claims that high doses (a.k.a. “mega-doses”) of vitamin C or ascorbic acid could prevent colds. Later Dr. Pauling’s irrational exuberance for mega-doses of ascorbic acid led to claims that it was also effective for treating at least some types of cancer. Years later, there is no credible evidence that mega-doses of vitamin C are effective for treating any cancer. However, at high doses, vitamin C can be harmful. For colds, it is possible that some people training hard in cold environments might benefit from a bit more than the RDA of vitamin C, but for most people it has no proven benefit. Nevertheless, today we have many people who still believe that mega-doses of vitamin C are healthy to take. You can find more on the duping of Linus Pauling in The Vitamin Myth: Why We Think We Need Supplements.
More recently we have seen irrational exuberance for mega-doses well in excess of the RDA for vitamin A (and beta-carotene), Vitamin E, Vitamin K, and, most recently, Vitamin D. The best research to date shows all these fat-soluble nutrients are toxic and claims that doses far in excess of the RDA are far more likely to cause harm over the long term than benefit (1).
While hardly news to most scientifically-trained RDs and clinical nutritionists, the simple truth is that almost no one benefits from taking supplements of vitamins well in excess of the RDA. If one is deficient in a nutrient, then taking more than the RDA for a while can be clinically justified, but for people who are not deficient in a nutrient in the first place, taking a supplement offers no known health benefit and may well be detrimental over the long term.
Perhaps the vitamin that was the most accepted as an effective treatment for disease was niacin and specifically nicotinic acid. For many years, mega-doses of vitamin B3 or niacin were prescribed to treat dyslipidemia. There is no doubt that high doses of niacin raise “good” or HDL-C levels. Niacin also may lower Lp(a) (another cardiovascular disease risk factor) and definitely lowers serum triglycerides and LDL-C levels. All these changes were long believed to help reduce the build up of cholesterol in the artery walls that contribute to most heart attacks and strokes in the US. Improving blood lipids with diet and drugs has been assumed to lead to a reduced risk of stroke and heart attacks. Because heart attack and stroke are the most common causes of death, illness, disability and reduced quality of life in industrialized countries, high doses of niacin far in excess of the RDA were assumed to be a way to cut the risk. Niacin (nicotinic acid) has long been considered an effective treatment to prevent cardiovascular disease. Despite niacin’s proven ability to lower cholesterol in the blood, which is one of the main risk factors for worsening atherosclerosis, proof it cuts the risk of dying from heart attacks and/or strokes is lacking. While long-term therapy with niacin was assumed to reduce the risk of heart attack and stroke, the evidence is limited.
Meta-Analysis of Studies Shows Niacin Ineffective
Researchers looked at 23 studies including 39,195 participants that compared niacin to placebo. Most of these studies included participants who were on average 65 years old and had already experienced a heart attack. The participants took niacin or placebo for a period of between six months and five years. Seventeen out of 23 studies were fully or partially funded by the drug manufacturer with a commercial interest in the results of the studies. Niaspan is an FDA approved drug for treating dyslipidemia.
The results of this study showed that niacin did not reduce the number of deaths, heart attack or stroke. Many people (18%) had to stop taking niacin due to side effects including flushing, itching, and GI problems. The results did not differ between participants who had or had not experienced a prior heart attack before they started taking niacin. The results did not differ between participants who were or were not taking a statin (or any other prescription drug that prevents heart attack and stroke) (2).
Bottom Line: The preponderance of quality research now shows that niacin (OTC or prescription forms) is ineffective for reducing the risk of CVD or total mortality. The next time there is a lot of hype about some vitamin in high doses being effective for preventing or treating disease, it is best to remain skeptical. To date the evidence of harm for high-dose vitamin supplements above the RDA appears to exceed any proven benefits.
By James J. Kenney, PhD, FACN
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.