Gross vitamin deficiency is often rare in Western societies, and you probably consume many vitamin-fortified processed foods without even realising. Many academic studies have found that multivitamins are unlikely to reduce the risk of chronic diseases, including cardiovascular disease and cancer, and some vitamin and mineral supplements have even be linked to increased health problems. The World Cancer Research Fund and the American Institute for Cancer Research recommend that you do not take dietary supplements for cancer prevention because the benefits are unpredictable and insignificant, and there could be possible side effects.
Let’s take a look at what overdoing it on certain vitamins can do to you. Excess iron can collect in body tissues, which damages your liver, heart or other organs. Vitamin C can inhibit the effect of chemotherapy drugs, and even help protect cancer cells, whilst your vitamin E supplements may interfere with your blood-thinner medications, and increase your risk of prostate cancer and all-cause mortality.
Vitamin A supplements have been linked to cancers, cardiovascular mortality, fractures (and low bone-mineral density) and increased birth defects when taken during pregnancy. It is true that studies have demonstrated that a diet rich in folate may reduce your cancer risk, but the same effect was not found in folic-acid supplements. In fact, some research has even indicated that patients who receive folic acid supplements are at an elevated risk of developing cancer.
Therefore it’s easy to see that though a multivitamin can supplement a specific nutrient you might need a little more of, at the same time your pill could be giving you too many of the nutrients you don’t need. You may need a specific supplement if you’re pregnant, over a certain age, have a medical problem or a specialised diet, or you’ve just had surgery, but in any case it’s best to consult your doctor before taking any supplement, and get your primary nutrients from your diet.