Niacin and CV Risk: Should Advice on Intake Change?

What Is the Optimum Niacin Intake?

Dr. Hazen noted that the recommended dietary allowance (RDA) for niacin is well known — between 14 and 18 mg, but he said the average American ingests four times that amount, and some people have substantially higher intakes — up to 50 times the RDA if taking supplements.

While food fortification with niacin may have been useful in the past, Dr. Hazen questioned whether it should still be mandated.

“In the US, you cannot buy flour or cereal or rice that is not fortified. And if you look closely, some products have much higher levels than those that are mandated. The food companies advertise this as a benefit, but there is no good data in support of that. What if several decades of eating excessive amounts of niacin has led to an increase in cardiovascular disease?”

He does not propose stopping all niacin fortification, “but maybe, we could have the choice of selecting an unfortified option,” he said.
 

Causal Link Not Proven

Commenting for this news organization, John Guyton, MD, Professor Emeritus of Medicine, Duke University Medical Center, Durham, North Carolina, who has been involved in niacin research for many years, said the Nature Medicine study showed “interesting and important results,” but they do not at this point prove a causal link between niacin intake and risk for cardiovascular disease.

“These findings need to be investigated further, and more studies are certainly justified, but I don’t think that this study alone makes an adequate case for restricting niacin intake, or thinking about stopping niacin fortification of foodstuffs,” Dr. Guyton said.

Noting that niacin is present in large quantities in many fast foods, he suggested the researchers may have just picked up the consequences of eating an unhealthy diet.

“If you look at foods that contain high quantities of niacin, red meat is at the top of the list. And if you think of a hamburger, niacin is present in relatively large quantities both the burger and the bun. So, these findings may just be a reflection of an overall unhealthy diet,” he commented.

Dr. Guyton also pointed out that major clinical trials with niacin have shown mixed results, and its effect on cardiovascular risk is still not completely understood. While the HPS2-THRIVE and AIM-HIGH trials did not show benefits in reducing cardiovascular events, an earlier study, the Coronary Drug Project in which the agent was given with food, did show some positive effects with substantial reductions in myocardial infarction and stroke, and there was the suggestion of a reduction in long-term mortality in the niacin group several years after the trial had ended.
 

Nicotinamide in Skin Cancer Prevention

What about the use of nicotinamide in skin cancer prevention?

Addressing this question, Kristin Bibee, MD, assistant professor of dermatology at Johns Hopkins University School of Medicine, Baltimore, pointed out that nicotinamide, although closely related to niacin, may have different effects. “This study does not specifically address nicotinamide supplementation and 4PY levels,” she said.

Diona Damian, MD, professor of dermatology at the University of Sydney, Camperdown, Australia, told this news organization that it was hard to extrapolate these findings on basal levels of niacin in a cardiac cohort to the administration of supra-physiological doses of nicotinamide for skin cancer prevention.

There may be different effects of supplemental niacin compared to nicotinamide, which lacks the vasodilatory effects seen with niacin, Dr. Damian said, adding that it would be interesting to see the results from higher, therapeutic nicotinamide doses in patients with and without cardiac disease.

She pointed out that high vs low levels of nicotinamide supplementation can have different and even opposite effects on cellular processes, such as upregulating or inhibiting DNA repair enzymes. At high doses, nicotinamide is anti-inflammatory in skin.

Dr. Damian noted that two phase 3 studies (ONTRAC and ONTRANS) of nicotinamide 500 mg twice daily for skin cancer prevention did not find a significant increase in cardiovascular events compared to placebo over 12 months.

“Oral nicotinamide has been shown to reduce nonmelanoma skin cancer by about a quarter in patients with normal immunity and multiple skin cancers. The doses used for skin cancer prevention are well above daily dietary levels, and treatment needs to be ongoing for the protective effects to continue. Nicotinamide should not be recommended as a preventive agent for people who have not had multiple skin cancers but should be reserved for those with a heavy burden of skin cancers,” she commented.

“For now, it would be reasonable to balance the benefits of skin cancer reduction against possible effects on inflammatory markers in patients with cardiac risk factors, when helping patients to decide whether or not nicotinamide therapy is appropriate for them,” she added.

Meanwhile, Dr. Hazen said the most exciting part of this new research is the discovery of a new pathway that contributes to cardiovascular disease and potentially a new target to treat residual cardiovascular risk.

“I believe our results show that we should be measuring 4PY levels and individuals with high levels need to be extra vigilant about lowering their cardiovascular risk.”

The next step will be to confirm these results in other populations and then to develop a diagnostic test to identify people with a high 4PY level, he said.

A version of this article appeared on Medscape.com.