People who take multivitamin and mineral supplements overstate the benefits, based on their positive expectations of effectiveness, researchers say today.
An observational study, in BMJ Open, compared self-reported and clinically measurable health outcomes among users and non-users of multivitamin/mineral supplements, using data supplied by a large, nationally representative sample of 21,603 US adults.
All had been asked about their use of complementary medicine in the 2012 annual National Health Interview Survey.
The researchers compiled five psychological, physical, and functional health outcomes from the questions asked: subjective assessment of health; need for help with routine daily activities; history of 10 long term conditions, such as high blood pressure and arthritis; presence of 19 common health conditions in the preceding 12 months, including infections, neurological and musculoskeletal problems; and degree of psychological distress, measured on a validated scale (K6).
Out of the cohort asked, 4,933 respondents said they regularly took multivitamin or mineral supplements, while 16,670 respondents said they did not.
Those who did take them reported 30% better overall health than those who did not, but there was no difference between the two groups in any of the five psychological, physical or functional health outcomes assessed.
Further analysis revealed that taking regular doses multivitamin or mineral supplements was associated with better self-reported overall health across all race, sex, and education groups, as well as in the under 65s and those on low household incomes.
The authors, led by Manish Paranjpe, of Harvard Medical School, Boston, caution that this is an observational study, so cannot prove a causal relationship between use of multivitamin/mineral supplements and subjectively assessed health.
However, they say the lack of any difference in the health outcomes assessed is in line with other studies.
“The effect of positive expectations is made even stronger when one considers that the majority are sold to the so-called worried well,” they say.
“The multibillion-dollar nature of the nutritional supplement industry means that understanding the determinants of widespread use has significant medical and financial consequences,” they add.
Paranjpe MD, Chin AC, Paranjpe I et al. Self-reported health without clinically measurable benefits among adult users of multivitamin and multimineral supplements: a cross-sectional study. BMJ Open 10 November 2020
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