Leaders in the medical research establishment took aim this week at dietary supplements, and multivitamins in particular, challenging their effectiveness in the fight to prevent heart disease, stroke and cancer.

The U.S. Preventive Services Task Force (USPSTF) issued new guidance Tuesday, saying it found "insufficient evidence" taking multivitamins, paired supplements or single supplements can help prevent cardiovascular disease (CVD) and cancer in otherwise healthy, non-pregnant adults.

The USPSTF analysis was based on a systematic review published this week in the Journal of the American Medical Association (JAMA). That review of 84 studies included 52 new studies since the last USPSTF recommendation on the topic in 2014.

The task force—which is described as an independent, volunteer panel of national experts in prevention and evidence-based medicine—went even further when it came to vitamin E and beta-carotene, recommending against taking either one to prevent CVD or cancer.

It found no benefit to taking vitamin E and concluded beta-carotene can be harmful because it increases the possibility of lung cancer in people already at risk.

A companion editorial in JAMA supporting the new task force guidance stressed the importance of evidence-based approaches that focus on balanced whole-food diets and physical activity when it comes to heading off CVD and cancer.

"The most common reason people report taking supplements is to improve or maintain overall health. However, whole fruits and vegetables contain a mixture of vitamins, phytochemicals, fiber and other nutrients that probably act synergistically to deliver health benefits" the editorial reads. "Micronutrients in isolation may act differently in the body than when naturally packaged with a host of other dietary components."

Dr. Jeffrey Linder, chief of general internal medicine at Northwestern Universitys Feinberg School of Medicine, was a co-author of the editorial and broadly challenged the efficacy of supplements and micronutrients in a press release about the JAMA publication.

Linder is quoted as saying his patients are "wasting money and focus thinking there has to be a magic set of pills that will keep them healthy when we should all be following the evidence-based practices of eating healthy and exercising."

"The task force is not saying dont take multivitamins, but theres this idea that if these were really good for you, wed know by now," Linder said.

What supplements potentially can do

Both the task force and JAMA editorial mention the new guidance is intended for healthy people without nutritional deficiencies or special nutritional needs, and supplements should play a role for people in which those deficiencies exist. For instance, the USPSTF does recommend women who are or might become pregnant take a folic acid supplement to aid child development.

Reaction from the supplement industry to the new guidance mostly focused on that aspect of the task forces findings, and other positive outcomes from clinical studies.

"Multivitamins fill in significant nutrition gaps in Americans," Andrea Wong, Ph.D., senior vice president of scientific and regulatory affairs with the Council for Responsible Nutrition (CRN), said in a statement. "Government data shows that most Americans fall short in many key nutrients."

Wong says FDA dietary guidance recognizes the under-consumption of calcium, potassium, dietary fiber and vitamin D, and that it is of public health concern because low intakes are associated with numerous negative health outcomes.

She further pointed to the Physicians Health Study II, a large-scale, randomized, double-blind, placebo-controlled trial that showed an 8% reduction in overall cancer risk in older male physicians who took a multivitamin.

Wong also cited the recent Cocoa Supplement and Multivitamin Outcomes Study (COSMOS), in which researchers found consuming cocoa flavanols lowered the risk of cardiovascular death by 27%. Cocoa flavanol supplements also showed promise in delaying cognitive decline in older people, according to Wong.

Notably, the COSMOS study also found taking a daily multivitamin did not have a significant impact on cardiovascular disease or cancer outcomes, a determination that tracks with the JAMA systemic review cited by the USPSTF.

Duffy MacKay, senior VP of dietary supplements with the Consumer Healthcare Products Association, noted in a statement that the USPSTF hadn’t changed the position it took in 2014, when it determined there is not yet enough evidence to determine if vitamin and mineral supplements help prevent CVD and cancer.

"However, dietary supplements should not be confused with drugs, and beyond the narrow focus of this review, the broader evidence base for the benefits of dietary supplements is growing rapidly," MacKays statement continues.

He additionally notes the National Institutes of Healths Office of Dietary Supplements believes supplementation can be helpful for people including those over 50, those who could become pregnant, breastfed babies and toddlers, those who avoid certain foods or who have poor diets, and many others.

NIH provides an online resource for consumers with fact sheets and other resources about hundreds of vitamins, minerals and micronutrients and their purported health benefits.