For years scientists have been saying there's not much evidence to recommend vitamin supplements for most people, with a growing body of research suggesting most of the pills are useless and don't necessarily make us any healthier.

Yet the message has not been getting through. Over half of US adults regularly take dietary supplements, fueling an industry worth some US$50 billion annually.

Enough is enough, researchers say. In the latest repudiation of vitamin supplements, the US Preventive Services Task Force (USPSTF) has now issued new recommendations, formally stating there is insufficient evidence to suggest supplements deliver benefits to prevent cardiovascular disease and cancer, the two leading causes of death in the US.

The new USPSTF recommendations – the first in relation to vitamin supplements since 2014 – were not arrived at lightly, but only after taking into consideration 84 studies assessing the effects of supplements, encompassing almost 740,000 participants in total.

"Unfortunately, based on the existing evidence, the Task Force cannot recommend for or against the use of most vitamins and minerals and is calling for more research," says USPSTF interim chief scientific officer John Wong.

There are some important caveats to bear in mind, however, as not all the findings were equivocal.

The new recommendations with regards to insufficient evidence of benefits only apply to healthy adults without nutritional deficiencies – and do not apply to people who are pregnant or trying to become pregnant, who are recommended to take folic acid supplements.

Further, while the USPSTF found the evidence was generally unclear for supplements overall for healthy, non-pregnant adults, for two products in particular, the data were less ambiguous: vitamin E and beta-carotene, both of which are not recommended to be taken.

"We found that there is no benefit to taking vitamin E and that beta-carotene can be harmful because it increases the risk of lung cancer in people already at risk," says USPSTF vice chair Michael Barry.

Apart from those limitations, though, the new recommendations essentially restate what many scientists have been telling us for years – there's no real proof these pills are good for us.

But at the same time – barring exceptional instances, like where supplements are tainted with hidden pharmaceutical ingredients – there's also not much to suggest they're bad for us, either.

"The Task Force is not saying 'Don't take multivitamins'," says clinician Jeffrey Linder, the chief of general internal medicine at Northwestern University's Feinberg School of Medicine.

"But there's this idea that if these were really good for you, we'd know by now."

Linder, the co-author of a new editorial commentary on supplements use and the new USPSTF recommendations, says there are good reasons why people believe supplements will be good for their health.

"In theory, vitamins and minerals have antioxidative and anti-inflammatory effects that should decrease the development of cardiovascular disease and cancer," the commentary, co-authored by Northwestern University researchers Jenny Jia and Natalie Cameron, explains.

"Eating fruits and vegetables is associated with decreased cardiovascular disease and cancer risk. It is reasonable to think that key vitamins and minerals could be extracted from fruits and vegetables, packaged into a pill, and people could avoid the difficulty and expense of maintaining a balanced diet."

Unfortunately, all the evidence we have doesn't really bear that assumption out, suggesting that, for reasons we still don't fully understand, micronutrients in isolation from other natural dietary components don't seem to offer the same health benefits as when they're bundled up and eaten in foods.

Even more unfortunately, the dietary supplement industry exploits people's misunderstanding on this ambiguous point, spending hundreds of millions of dollars every year to perpetuate false beliefs about the powers of vitamin pills.

It's not just money, at stake, either. Scientists worry that people's health is at risk, too, simply because there's a significant opportunity cost every time a patient's focus is misdirected – with evidence-based health care losing out to infinite formulations of snake oil.

"[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," Linder says.

"The harm is that talking with patients about supplements during the very limited time we get to see them, we're missing out on counseling about how to really reduce cardiovascular risks, like through exercise or smoking cessation."

The new recommendations are published in JAMA, along with an overview of the research behind the recommendations, and the accompanying editorial article.