A few decades ago, when supplements were still in small demand, the ingredients supply seemed inexhaustible. But during the past 15 years, the booming global supplements market has put a squeeze on natural resources. Medicinal roots, such as goldenseal, ginseng (above), and black cohosh, are at particular risk because harvesting them kills the plant. “In the past, these herbs have not been cultivated; they've come only from the wild,” explains Sara Katz, founder of Herb Pharm herbal-extract company. “That's a completely unsustainable practice.” Meanwhile, overfishing is a major issue affecting manufacturers of fish-oil softgels; nearly 70 percent of the planet's fish stocks are overharvested, according to the United Nations.

So how can you tell if your supplement contains responsibly harvested ingredients? It depends on the product. Unfortunately, there is no one certification for — or definition of — sustainability. For herbal formulas, look for the USDA Organic seal, which assures the herbs were either cultivated on a farm or responsibly harvested from the wild. Traditional Medicinals audits suppliers to ensure ingredients meet international ecological, social, and quality standards. For fish oils, choose high-quality brands such as Nordic Naturals, which sources only from sustainable species, such as anchovies and sardines, rather than overfished tuna or salmon. And you can always call the manufacturer to ask where and how ingredients are sourced.