AMERICANS love supplements. About half of adults take them regularly. They buy them with precise goals—for their hearts, joints and intestines—but mostly with the vague hope that they will make them healthier. This optimism supports a big industry. Last year American sales of supplements reached a record $25 billion, according to Euromonitor, a market-research firm. Americans are not alone. Global sales of supplements reached nearly $90 billion in 2014. This success is built on the assumption that pills contain certain ingredients that bring certain benefits. But do they? Everyone needs vitamins. These chemicals act as tiny aides in the body, supporting reactions that help us live. The debate comes down to whether supplemental vitamins are of good quality and whether they actually do any good, particularly in prosperous countries, where people tend to have better access to a diet rich in vitamins than in poorer countries. Other types of supplements, including herbal products and homeopathy, are even more controversial.

It is hard to be confident of supplements' quality and even more difficult to decipher their promised benefits. Companies such as GNC, which sells health products, say they have thorough measures to assure safety and quality. New York's attorney-general made headlines this year by accusing firms of selling pills with bogus ingredients; his tests were likely faulty. However problems remain. The Food and Drug Administration (FDA) does not review supplements' safety or efficacy before they go to market. There are manufacturing standards for supplement makers, but not the suppliers of ingredients. There is no cap on the amount of a nutrient that may be in a pill, nor on the combinations of ingredients it may contain. Meanwhile companies have broad freedom to market the benefits of their pills. They cannot claim to treat or prevent a disease, but they can use phrases such as “supports heart health” and “supports healthy bones”. Companies need not give the FDA proof for their claims. When a government auditor reviewed some companies’ evidence in 2012, several offered links to Wikipedia. One company presented a 30-year-old college paper.

As a result, scandals are common. In 2013 women taking vitamin B sprouted facial hair—it turned out their pills contained steroids. That year consumers on a diet pill developed acute hepatitis. One died and at least three had liver transplants. The market is also stocked with supplements that claim to do good, despite meagre evidence. There are indeed supplements that are beneficial. For example, women who plan to become pregnant should take folic acid. The elderly should take vitamin B12, as they have trouble digesting the natural form. But the evidence for most supplements is mixed at best. Beta-carotene, a precursor to vitamin A, seems to raise the risk of lung cancer among smokers. A study in 2011 reported that men taking vitamin E were more likely to develop prostate cancer. Two studies have suggested that multivitamins may lower the risk of cancer in men; another found a link between multivitamins and fewer deaths from heart disease in women. But in 2013 a trio of papers reported that multivitamins showed no clear effect on heart disease, cancer, cognitive decline or death.

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Despite scandals and scepticism, America’s supplement industry is booming (September 2015)