A vitamin a day keeps the doctor away? Not quite.

More and more scientific research is showing that the health benefits of vitamins might be less spectacular than advertised. But Americans still keep swallowing the message – to the tune of around $11 billion a year, according to the Nutrition Business Journal. But while vitamins may be beneficial in very specific circumstances, many consumers may be counting on a silver bullet that’s a dud at best.

The most recent example comes from a group of French and Belgian researchers that took a look at the benefits of vitamin D. This “sunshine vitamin” found in eggs, fish, fortified milk (and made by your body when exposed to sunlight) has long been known to help keep bones healthy, but low levels of vitamin D have been implicated in lots of other conditions, too, from heart disease to cancer to Parkinson’s. As a result, many people have been taking vitamin D supplements as a way to protect against these conditions.

But the problem, the French-led team wrote this week in The Lancet Diabetes & Endocrinology, is that vitamin D supplements don’t seem to actually prevent any ailments aside from bone-related problems. While observational studies that measure vitamin D levels in a person’s showed that high blood levels of the vitamin were associated with lower risks for heart disease, diabetes and colon cancer, clinical trials of vitamin D failed to budget people’s disease risks, with one exception – older people. This can likely be chalked up to the fact that vitamin D supplements help strengthen bones, which would probably result in fewer deaths among seniors that fall and fracture their bones.

Ultimately, the researchers think that low vitamin D levels aren’t a cause of cancer or diabetes or any of the other conditions implicated; instead, they’re a symptom. Illnesses might reduce your blood levels of vitamin D, in other words, but taking a bunch of vitamin D beforehand probably won’t prevent the illness.

But other scientists don’t want Americans to flush all their supplements down the drain just yet.

While the paper does highlight the need for more long-term studies, “it does not suggest that taking vitamin D supplements can not be useful in some cases for some purposes,” Nigel Belshaw, a researcher at Britain’s Institute of Food Research, told Reuters. “Neither does it rule out a health advantage of increasing vitamin D levels in the blood for those who are deficient."

The vitamin D study comes on the heels of a broader look at vitamins published in the Annals of Internal Medicine in November. In a meta-analysis, a team of researchers from the U.S. Preventive Services Task Force reviewed 24 studies of individual vitamins, minerals and other supplements.

“Across all the supplements studied, there was no evidence of beneficial effects on cardiovascular disease, cancer, or all-cause mortality,” the authors wrote.

In certain cases, vitamins can even hurt. In 2011, researchers from the Cleveland Clinic reported in the Journal of the American Medical Association that a daily dose of vitamin E, touted as a way to reduce a man’s risk for prostate cancer, actually had the opposite effect. In a clinical trial of vitamin E and selenium involving more than 35,000 men, study participants that took vitamin E supplements alone had a significantly higher risk for prostate cancer than men that took placebo, or selenium, or both vitamin and selenium. A 2008 study from another group linked vitamin E to a raised risk for lung cancer as well.

“We call [vitamins] essential nutrients because they are,” Marian L. Neuhouser, a researcher at the Fred Hutchinson Cancer Research Center in Seattle, told the New York Times in 2009. “But there has been a leap into thinking that vitamins and minerals can prevent anything from fatigue to cancer to Alzheimer’s. That’s where the science didn’t pan out.”