Growing numbers of healthy people are taking dietary supplements but there is little evidence that they protect against non-communicable diseases
Vitamin and mineral supplements are the most commonly used dietary supplements by populations worldwide. While supplements can be used to correct micronutrient deficiency or maintain an adequate intake, over-the-counter supplements are most often taken by people with no clinical signs or symptoms of deficiency. However, the effect of vitamin and mineral supplements on the risk of non-communicable diseases in “generally healthy” populations is controversial. We examine patterns of supplement use and the evidence on their effects from randomised trials.
Randomised trial evidence does not support use of vitamin, mineral, and fish oil supplements to reduce the risk of non-communicable diseases
Do supplements protect against non- communicable diseases?
An updated systematic review of 15 randomised trials published after the 2013 US Preventive Service Task Force (USPSTF) review20 confirmed the lack of benefits of supplements on cardiovascular events, mostly among patients with risk factors. Although randomised trials of folic acid, alone or in combination with vitamins B12 or B6, found significant reductions in plasma homocysteine levels, total cardio- vascular events were not reduced. Another systematic review reported a reduced risk of stroke in association with supplementation of homocysteine lowering B vitamins, but the results was largely driven by one large trail in China.
Type 2 diabetes
Current evidence does not support the use of supplements with vitamins C or E, β-carotene, or fish oil to reduce the risk of type 2 diabetes, although the overall evidence from randomised trials is limited.
A recent placebo controlled trial of vitamin D supplementation (4000 IU/day) failed to reduce the risk of type 2 diabetes despite significantly increasing serum 25-hydroxy-44 vitamin D concentrations.
Recent evidence regarding the effects of vitamin D and calcium supplementation is inconsistent. A meta-analysis of trials in community living older adults found that vitamin D or calcium supplementation did not reduce the risk of hip fracture or total fracture,45 whereas another meta-analysis reported that while vitamin D alone did not reduce fracture risk, combined calcium and vitamin D supplementation decreased the relative risk of hip fracture (16%) and all fractures (6%) among older adults. Ongoing research is assessing the effect of high dose vitamin D supplements on several health outcomes, including fractures, but a recent three year trial of 400, 4000, or 10 000 IU/day reported that the higher doses reduced volumetric bone density, suggesting potential for harm.47 In the absence of clear evidence on supplementation, it is prudent to ensure that dietary recommendations on calcium and vitamin D intakes are met through food and supplementation.