Three in four Americans take a dietary supplement every day, says a new study on multivitamins, which found that together the US spends around$30 billion per year on vitamins and supplements.
However, a new study led by researchers at Harvard Medical School in the US found very little evidence that multivitamins or mineral supplements have any positive impact on health, except for people with known vitamin or mineral deficiencies. The study suggested that while many people taking daily vitamins claim that it makes them feel better, in most cases that is likely just a placebo effect.
The researchers compared self-reported and clinically measurable health outcomes among a group of more than 21,000 multivitamin users and non-users in the United States. Of these, 4,933 said they regularly took multivitamins or mineral supplements while 16,670 said they did not.
The study found that the supplement users reported 30 percent better overall health than those who did not take supplements. But when the psychological, physical and functional health of these supplement users were clinically assessed, they were found to score no higher than non-users.
The study used data from the National Health Interview Survey (NHIS), which has been monitoring health of US citizens since the late 1950s. The questionnaire in 2012, on which the new study is based, asked questions on subjective self-assessments of health, including the need for help with routine daily activities as well as personal history of long-term conditions such as high blood pressure, asthma, diabetes, and arthritis.
It also asked about the presence of common health conditions in the preceding 12 months, including infections, memory loss, neurological and musculoskeletal problems, and individuals’ degree of psychological distress.
The study results suggest that widespread use of multivitamins in adults may be a result of individuals’ positive expectation that multivitamin use leads to better health outcomes, or a self-selection bias in which multivitamin users intrinsically harbor more positive views regarding their health.
The study found that, compared to non-users, people who regularly took vitamins were older and had higher household incomes. They were also more likely to be women, college graduates, married, and to have health insurance. Many of these factors are already associated with better health and quality of life.
The researchers admitted that their study had limitations as the observational study relied on self-reported vitamin use and health assessments. Researchers also did not look at how health assessments may have changed before and after beginning to take vitamins regularly.
The team also added that there was some evidence supporting vitamin and mineral supplementation in certain circumstances, such as folic acid for people during pregnancy and vitamin D supplements for older adults, particularly those who get limited sun exposure.