Other antioxidant supplements that showed some evidence of reducing cardiovascular risk were omega-6 fatty acids, L-arginine, L-citrulline, magnesium, zinc, alpha-lipoic acid, melatonin, catechin, curcumin, flavanol, genistein, and quercetin.
No effect was seen with vitamin C, vitamin D, vitamin E, or selenium, and beta-carotene supplementation was linked to an increase in all-cause mortality in the analysis.
The study is published in the Journal of the American College of Cardiology and was also published online.
“Our systematic assessment and quantification of multiple differential effects of a wide variety of micronutrients and phytochemicals on cardiometabolic health indicate that an optimal nutritional strategy to promote cardiometabolic health will likely involve personalized combinations of these nutrients,” the authors, led by Peng An, PhD, China Agricultural University, Beijing, conclude.
“Identifying the optimal mixture of micronutrients is important, as not all are beneficial, and some may even have harmful effects,” senior author Simin Liu, MD, professor of epidemiology and medicine at Brown University, Providence, R.I., said in an American College of Cardiology press release.
“The micronutrients identified require further validation in large, high-quality interventional trials to establish clinical efficacy to determine their long-term balance of risks and benefits,” the authors add.
Experts cautious
Experts in the field of cardiovascular risk and preventative medicine have urged caution in interpreting these results.
JoAnn Manson, MD, chief of the division of preventive medicine at Brigham and Women’s Hospital, Boston, told this news organization that she has concerns that some of the results in the meta-analysis may be inflated by publication bias and some are chance findings that haven’t been well replicated.
“Although this meta-analysis of micronutrients and cardiometabolic health was based on randomized clinical trials, the quality of randomized trials on this subject varies widely,” she noted.
“The study is informative, but the conclusions are only as good as the quality of the evidence. Some of the trials are limited by short duration, and included trials have a wide range of quality, dosing, inclusion criteria, imperfect blinding, and few of them focus on hard clinical events,” Dr. Manson said. “Also, with trials of this nature, the potential for publication bias warrants consideration, because many of the smaller trials with unfavorable or neutral results may remain unpublished or not even be submitted for publication.”
However, she added, “despite these limitations, this is an important contribution to the literature on micronutrients and health – and goes a long way in separating the wheat from the chaff.”
Steve Nissen, MD, chief academic officer of the Heart Vascular and Thoracic Institute at the Cleveland Clinic, was more critical of the meta-analysis.
“This study does not make sense. Some of the ‘micronutrients’ in this meta-analysis have undergone thorough testing in large randomized clinical trials that showed different results. I am skeptical whether any of the purported benefits of these supplements would be confirmed in a high-quality randomized controlled trial,” he said.
Dr. Nissen added that many of the included studies are low in quality. “I must quote [renowned cardiologist, Dr.] Franz Messerli: ‘A meta-analysis is like making bouillabaisse. ... One rotten fish can spoil the broth.’ This type of analysis does not override high-quality large, randomized trials.”
In the JACC paper, the study investigators note that the American Heart Association now recommends dietary patterns, including the Mediterranean diet and DASH (the Dietary Approach to Stop Hypertension), as preventive or treatment approaches for cardiovascular disease. A common feature of these dietary patterns is that they are low in saturated fat and sodium and rich in micronutrients such as phytochemicals, unsaturated fatty acids, antioxidant vitamins, and minerals.
“To personalize cardiometabolic preventive and therapeutic dietary practices, it is of critical importance to have a comprehensive and in-depth understanding of the balance of benefits and risks associated with constituent micronutrients in diverse dietary patterns,” they note.
They therefore conducted the current systematic review and meta-analyses of all available randomized controlled trials investigating the effect of micronutrients with antioxidant properties on cardiovascular risk factors and events in diverse populations.
The meta-analysis included a total of 884 randomized trials evaluating 27 types of micronutrients among 883,627 participants.
Results showed that supplementation with n-3 fatty acids, n-6 fatty acids, L-arginine, L-citrulline, folic acid, magnesium, zinc, alpha-lipoic acid, coenzyme Q10, melatonin, catechin, curcumin, flavanol, genistein, and quercetin had “moderate-to high-quality evidence” for reducing cardiovascular risk factors.
Specifically, n-3 fatty acid supplementation was linked to reduced rates of cardiovascular mortality (relative risk, 0.93), myocardial infarction (RR, 0.85), and coronary heart disease events (RR, 0.86). Folic acid supplementation was linked to a decreased stroke risk (RR, 0.84) and coenzyme Q10 was associated with a lower rate of all-cause mortality (RR, 0.68).
“The current study represents the first attempt in providing a comprehensive and most up-to-date evidence map that systematically assessed the quality and quantity of all randomized trials linking the effects of a wide variety of micronutrients on cardiovascular risk factors,” the authors say.
“The comprehensive evidence map presented here highlights the importance of micronutrient diversity and the balance of benefits and risks in the design of whole food–based dietary patterns to promote cardiometabolic health, which may require cultural adaptations to apply globally,” they conclude.
Commenting on some of the specific beneficial findings, Dr. Manson said: “I do believe that the marine omega-3s confer heart benefits, but results are not consistent and vary by dose and formulation.”
However, she pointed out that, regarding folic acid, a previous meta-analysis including eight large randomized trials in more than 37,000 participants found no reduction in coronary events, stroke, or major cardiovascular events with folic acid supplementation, compared with placebo, “so the reported stroke benefit would need further confirmation.”
In an accompanying editorial, Juan Gormaz, PhD, University of Chile, and Rodrigo Carrasco, MD, Chilean Society of Cardiology and Cardiovascular Surgery, both in Santiago, state: “Given that the compounds with more pleiotropic properties produced the better outcomes, the antioxidant paradigm on cardiovascular prevention can be challenged. For example, inasmuch as n-3 fatty acids have antiplatelet and anti-inflammatory properties, they are too complex to enable attribution of the observed benefits solely to their antioxidant capacity.”
The editorialists note that from a research point of view, “although the current information opens interesting perspectives for future consolidation of some antioxidants in preventive cardiology, there is still a long way to go in terms of generating evidence.”
They add that the challenge now for some compounds is to begin establishing consensus in definitions of dose and combinations, as well as continue strengthening the evidence of effectiveness.
“Regarding routine clinical practice, these results begin to open spaces for the integration of new tools into the therapeutic arsenal aimed at cardiovascular prevention in selected populations, which could be easily accessible and, with specific exceptions, would present a low frequency of adverse effects,” they conclude.
This work was partly supported by the United States’ Fulbright Program and by the Beijing Advanced Innovation Center for Food Nutrition and Human Health, the National Natural Science Foundation of China, the Chinese Universities Scientific Fund, and the Beijing Municipal Natural Science Foundation.
Dr. Liu has received honoraria for scientific presentations or reviews at Johns Hopkins University, Fred Hutchinson Cancer Center, Harvard University, University of Buffalo, Guangdong General Hospital, Fuwai Hospital, Chinese Academy of Medical Sciences, and the National Institutes of Health; he is a member of the Data Safety and Monitoring Board for several trials, including the SELECT (Semaglutide Effects on Cardiovascular Outcomes in People with Overweight or Obesity) trial sponsored by Novo Nordisk and a trial of pulmonary hypertension in diabetes patients sponsored by Massachusetts General Hospital; he has received royalties from UpToDate and has received an honorarium from the American Society for Nutrition for his duties as Associate Editor. Co-author Jeffrey Mechanick, MD, has received honoraria from Abbott Nutrition for lectures and serves on the advisory boards of Aveta.Life, L-Nutra, and Twin Health. The other authors report no relevant financial relationships.
A version of this article first appeared on Medscape.com.