Although the idea of vitamins (initially “vitamine” from “vital amine”* (1)) was conceived in the early 1900s, it wasn’t until the 1930s that scientists discovered that they could be artificially synthesised (2). Twenty years later, multivitamins and multimineral complexes (called MVMMs) would be widely consumed based on the belief that they were beneficial for one’s health (3).
Nowadays almost everyone takes MVMMs, and the nutraceutical market has grown into a multibillion-dollar industry. Despite their popularity, MVMMs have received a significant amount of flak in the past year due to the documented inefficacy in healthy individuals. There are several research papers documenting MVMMs ineffectiveness, and some recent findings indicate that MVMMs can be harmful (4, 5, 6, 7, 8, 9, 10, 11).
It’s not unexpected that high doses of some vitamins are harmful; after all, “the dose makes the poison” and anything – including water – in a high enough dose can kill. However it is unexpected that taking moderate doses of certain vitamins can be harmful. Some ingredients in MVMMs that can harm more than help are vitamin A, folic acid, iron with vitamin D, and possibly vitamin D.
The negative effects of beta-carotene (a precursor to vitamin A) on smokers has been known for two decades, and gave scientists the first inkling that vitamin supplements could be harmful. There is a well-established correlation in the scientific literature between beta-carotene supplementation (by smokers) and lung cancer (12). Most non-smokers ignore this, but this finding was only the beginning.
Folic acid, the synthesised form of B9, is well-known by women who are trying to conceive or pregnant. After the finding in 1964 that folic acid supplementation reduced neural tube defects, the pill became widely prescribed to pregnant women (and mandatorily added to food) (13, 14, 15).
Despite its supposed benefit, an increased susceptibility to multiple cancers has been associated with folic acid in recent years. Excessive folic acid – especially when it is unmetabolised, as happens often with synthetic B9 – can stimulate tumour growth (16, 17, 18, 19, 20). Some researchers chalk this up to folic acid being inherently different from the naturally occurring form in food, tetrahydrofolate. The research is still unclear, but it’s probably a good idea to avoid MVMMs with folic acid (unless you’re pregnant).
Regular doses of vitamin D have recently been correlated with increasing the severity of cardiovascular disease (21, 22, 23). The proposed mechanism involves vitamin D increasing calcium levels (which can contribute to plaque calcification) (24). (Excess can build up after taking a low dose of vitamin D over the long term**.)
Perhaps the most surprising finding on the harmfulness of some vitamins was on vitamin C and iron. Vitamin C is believed to increase the absorption and uptake of iron in the gastrointestinal tract, so many doctors will advise iron deficient patients to take a hefty dose of vitamin C alongside iron supplements. Apparently, this has been linked to a drastic increase in risk of cancers in the GI tract (25, 26, 27).
If you’re a relatively healthy individual, it’s best to avoid supplementation of a number of vitamins and/or minerals. Some people consider MVMMs “health insurance”, although there is clearly a dark side to some complexes.
(Don’t take MVMMs; if you’re going to supplement, it should be targeted.)
*The “e” on “vitamine” was dropped when scientists realised that not all vitamins contain amines.
**The “long term” is apparently “three months or more”.
– Jennifer Labrie
