They were some of the most promising medicines of the 1990s — wonder pills that appeared to fight cancer, heart disease, stroke and other ailments.

Laboratory tests and initial studies in people suggested that lowly vitamins could play a crucial role in preventing some of the most intractable illnesses, especially in an aging population. The National Institutes of Health gave them the same treatment as top-notch pharmaceutical drugs, investing hundreds of millions of dollars in elaborate clinical trials designed to quantify their disease-fighting abilities.

Now the results from those trials are rolling in, and nearly all of them fail to show any benefit from taking vitamin and mineral supplements.

This month, two long-term trials with more than 50,000 participants offered fresh evidence that vitamin C, vitamin E and selenium supplements don’t reduce the risk of prostate, colorectal, lung, bladder or pancreatic cancer. Other recent studies have found that over-the-counter vitamins and minerals offer no help in fighting other cancers, stroke or cardiovascular disease.

Research has even suggested that in some circumstances, the supplements can be unsafe.

Some physicians now advise their patients not to bother with the pills, and to rely instead on a healthy diet to provide needed vitamins and minerals.

“These things are ineffective, and in high doses they can cause harm,” said Dr Edgar R Miller, a professor of medicine and epidemiology at Johns Hopkins University School of Medicine in Baltimore. “People are unhappy with their diets, they’re stressed out, and they think it will help. It’s just wishful thinking.”

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