Taking supplements is common among U.S. adults, and the most oft-cited reasons people give for taking them are wanting to feel better, improving energy levels and boosting the immune system, a new survey finds.

But these aims have little to do with measurable improvements to health, the researchers said. Moreover, most people taking supplements indicated that the supplements’ proven effectiveness didn’t matter to them — only 25 percent said they would stop taking a supplement if it was found to be ineffective, according to the survey.

“We call this the ‘effective for me’ attitude,” said study researcher Kathleen Weldon, of the Harvard School of Public Health in Boston. “As long as something is safe, people think they are a better expert on whether it works for them, better than any clinical trial.”

People who put stock in effectiveness data tend to be “taken aback” by such thinking, she said, and wonder why a person would keep taking a supplement that hasn’t been shown to work. “It’s a very interesting thing to think about, in terms of scientific validity,” she said. “But it’s hard to argue against —what if this person is the one in a million that it’s doing something for?”

The findings are based on data from a nationally representative sample of about 1,600 adults.

Participants reported using a range of products, including herbal supplements such as ginseng, probiotics such as acidophilus, amino acids, garlic pills and supplements derived from algae.  (The researchers told the study participants not to include vitamins or minerals they were taking.)

About 38 percent said they had taken a dietary supplement in the last two years, and 1 in 7 reported taking supplements regularly, the survey showed. These findings are in line with what other studies have found, Weldon said.

The most commonly used supplement was fish oil, or other omega-3 fatty acid supplements — about 24 percent of adults have used them in the last two years.

More than a third of participants said they hadn’t told their doctor about their supplement use.

“People should tell their doctors what they’re taking,” Weldon said. Supplements may interact with a patient’s prescription medications, he said.

Another reason to tell the doctor is to make them aware of health conditions the patient is trying to treat with a supplement, she said. “Sometimes, people take supplements to lower their high cholesterol, treat arthritis or high blood pressure, to treat digestive issues — as part of the picture of good care, that communication should be there.”

The article was published Nov. 19 in the journal Archives of Internal Medicine.

Pass it on: Supplements’ effectiveness doesn’t matter to many people who take them, a new survey finds.

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