Over 60% of Australians take some form of vitamin or mineral supplement, and the complementary medicine industry in this country alone was worth around $3.5 billion in 2016. Many doctors will roll their eyes at such expenditure and possibly blame pharmacists for providing these products with a sheen of medical plausibility. But it’s worth asking what exactly the evidence is for supplements, whether there are patients who should be taking them, and what doctors should be telling their patients about them.
A new viewpoint published in JAMA lays out the evidence for vitamin and mineral supplements. It notes that the vast majority of randomised clinical trials of supplements have not shown benefits for the prevention of chronic diseases not related to nutritional deficiency. Indeed, some trials have shown harms with high doses of micronutrient supplements, including increased risk of stroke, cancer and death.
The upshot is that doctors “should counsel their patients that supplementation … provides little if any benefit,” the Boston-based authors say.
But although supplements aren’t recommended for the general population, there are high-risk groups for whom they may be a good idea, they note. These are:
- Pregnant women, for whom 0.4-0.8mg/d folic acid is recommended for preventing neural tube defects. Supplemental iron might also be needed in pregnant women with low levels of haemoglobin or ferritin. Calcium and vitamin D supplementation may provide benefits, but confirmatory trials are needed.
- Children who are exclusively or partially breastfed could benefit from supplemental vitamin D (400IU/d) from soon after birth, along with supplemental iron (1mg/kg/d) from 4 months. But healthy children on a balanced diet have no need for supplements.
- Adults over 50 may benefit from vitamin B12, vitamin D or calcium supplementation, but only if their levels of these are lower than recommended.
Clinicians should always ask about use of micronutrient supplements if patients are taking other drugs, to ensure there are no unwanted interactions. For example, vitamin K supplements could lessen the effects of warfarin, while vitamin B7 can interfere with the accuracy of troponin testing.
At the same time, it’s best to not be too judgemental of a patient’s use of vitamin and mineral supplements, given their prevalence in the general population.
You can access the Viewpoint here.