Introduction to dietary supplements: the good, the bad and the ugly

There are two common misconceptions about dietary supplements: firstly that the more the better, and secondly that they can be taken to make up for a poor diet. Research into the value of supplements in both disease treatment and prevention is still ongoing, and there is often conflicting evidence associated with supplement intake. It seems increasingly clear that, despite scepticism, some supplements do have the potential to promote health by preventing certain diseases and conditions, but in other cases they can lead to serious side effects, including a suggestion that some may increase the risk of cancer. For example, the risk of lung cancer in high risk populations is significantly increased in those who consume 20-30mg/day of B-carotene. Another study showed a wide range of potentially damaging effects from taking calcium supplements, including the doubling of hospital admissions for gastrointestinal problems, 17% increase in kidney stones and 20-40% increase in the risk of a heart attack in those taking calcium supplements.

Dietary supplements can have specific benefits, though, for example it has long been known that taking folic acid during pregnancy reduces the development of birth defects. The risks of developing certain diabetic complications such as heart disease and neuropathy are known to be reduced by taking supplements of omega-3 and alpha-lipoic acids. There are also many severe medical conditions that are the direct result of nutrient deficiencies, possibly as the result of malabsorption, which can be reversed, or at least managed, by appropriate supplementation. These include bone fragility, anaemia, nervous system abnormalities and poor immune system functionality. Some deficiencies are actually classed as a condition in their own right (for example iron or vitamin B12 deficiencies).

However, despite their potential beneficial effects, caution should be taken when using dietary supplements. As they are not classed as medicines or food, and thus they are not subject to the same manufacturing regulations as these products. Furthermore, due to insufficient evidence as to their impact on health, supplements should not legally make any claims regarding effects on health, although many do, and they are not officially intended to diagnose, treat, cure or prevent disease. Supplements are therefore manufactured without the rigorous safety and efficacy testing demanded by law for any true medicinal product. In fact supplements are often manufactured from synthetic materials, such as hydrogenated sugar extracts or petrochemicals, and may contain genetically modified ingredients, artificial sweeteners and even carcinogenic substances.

Some supplements are marketed as having “almost no side effects”, but when combined with other substances, or taken too frequently, can quickly become toxic. For example, large doses vitamin C or magnesium can cause diarrhoea, whereas excess iron intake is generally associated with constipation as well as abdominal pain, nausea and vomiting. Worryingly, dietary supplements can also interact with prescribed medications with serious and even life-threatening results, e.g. warfarin, insulin and aspirin have many recorded adverse reactions when taken with dietary or herbal supplements. In addition to these interactions, fat soluble vitamins such as vitamins A, D, E and K, can accumulate in the body if doses above the recommended daily limit are routinely taken. This toxicity can result in mental symptoms such as confusion and physical symptoms, such as liver damage and even death.

There are many reasons, to think twice about taking dietary supplements. There is a distinct lack of regulatory control, with none of the requirements that are required for medication approval in addition to the potential for adverse interactions with prescribed and over-the-counter medications. Far from being beneficial, some dietary supplements can actually cause serious harm when taken in excessive amounts or at the same time as other medications. The amount that is right for you will depend on numerous factors, and the recommended daily intake is not the one-size-fits-all that supplement manufacturers claim it is.