One out of every two adults in the U.S. takes a dietary supplement on a routine basis, and a closer look at the data of a study reveals a number of trends.

The overall use of dietary supplements has remained steady over the past decade-plus, with 52 percent of the population taking at least one supplement. But the number of American adults taking daily multivitamins has declined from 37 percent in 1999 to just 31 percent in 2012, according to a study appearing in the Oct. 11, 2016 issue of the Journal of the American Medical Association (JAMA).

Credit: Steven Depolo/Flickr, CC BY 2.0

The overall rates are steady because U.S. adults have shifted gears from multivitamins to other options. The JAMA study, which tracked the supplement use of nearly 38,000 adults, shows that Americans are diving into a whole new world of dietary aids, including probiotics and supplements such as vitamin D, on a routine basis.

“Many supplements, including vitamins, minerals and probiotics, are important components of modern health care,” states Pieter A. Cohen, M.D., in an editorial accompanying the research study.

Probiotics, which have a long history in other cultures due to their perceived positive health impact, are essentially bacteria and other microorganisms that are intended to provide health benefits. Probiotics are often referred to as “friendly bacteria” or “good bacteria,” according to the National Center for Complementary and Integrative Health (NICCH), part of the federal National Institutes of Health (NIH).

Related: Good Bacteria Can Limit E. Coli, Salmonella Infections

You’ll find probiotics in certain yogurts that aim to improve gastrointestinal health, for example. In fact, probiotic therapy containing the bacterium Lactobacillus GG has proven effective in the treatment of diarrhea in infants and children, says a health guide from Harvard Medical School. Studies have also shown that probiotics may be helpful in treating ulcerative colitis and Crohn’s disease, two disorders affecting the gastrointestinal tract.

Are probiotics safe? The consensus appears to be ‘yes.’ “In people who are generally healthy, probiotics have a good safety record,” states the NICCH. If you’re one of the Americans not yet taking probiotics, you’re likely more familiar with them than you realize. As a live form of bacteria or other microorganism, probiotics are similar to millions of microorganisms that live in our gut. 

Note that most probiotics are sold as dietary supplements, which do not require approval of the Food and Drug Administration (FDA) to be marketed to consumers.

Fish Oil, Vitamin D Rise; Previous Mainstays Fall

More Americans are taking fish oil supplements, according to the study. In 2012, 12% of the adult population reported taking a form of fish oil, which is mainly used for heart health, up from just 1.3% who reported taking fish oil in 1999.

Also on the rise are vitamin D supplements as a single dose not contained in a multivitamin. Nearly one-fifth of adults, or 19%, reported taking standalone vitamin D supplements in 2012, compared to only 5.1% about a decade earlier.

Cohen, in his editorial, notes that a “string of negative studies involving supplements” may have led to Americans ditching the most popular ones from 10 years ago, including multivitamins, vitamin E and vitamin C.

Related: Testing Your Tears Could Reveal What Vitamins You Need