The Archives of Internal Medicine has published the results of an observational study that has linked the use of some vitamin and mineral supplements with an increased risk of mortality. This has been reported in general media (BBC).
This study reviewed data from the Iowa Women's Health Study. 38,772 women with an average age of 61 years self-reported supplement use at three time points (1986, 1997 and 2004). 15,548 deaths were identified through State and National recording systems to the end of 2008.
After correction for several factors including age, smoking status, body mass index, hypertension, diabetes and education it was noted that use of multivitamins, vitamin B6, folic acid, cooper iron, magnesium and zinc were all associated with an increased risk of mortality when compared with non-users. Only one of the fifteen supplements analysed (calcium) was linked to a decrease in mortality.
The study authors note several limitations in their findings. Firstly, the participants in the study were exclusively women and 99.2% were white and 98.6% were postmenopausal. The results of this analysis may therefore not be applicable to other patient groups.
Secondly, the data are observational and there may be residual confounding factors that were not corrected for, such as underlying illnesses. Finally, the study did not analyse the impact of these supplements on quality of life however it has raised concerns about long-term safety.
The authors of the study state that there is "little justification for the general and widespread use of dietary supplements" and that use should be based upon a "strong medically based cause, such as symptomatic nutrient deficiency disease".
Action: Clinicians should be aware of this study. Individual patients who consume a well balanced diet can be advised that supplements are unnecessary and may be harmful.