The quality of food supplements varies considerably. It is safest to buy from a reputable brand and retailer. Some food supplements purchased on the internet can contain substances which are not permitted for use within the EU, and in some cases have been found to be contaminated with pharmaceutical medicines or heavy metals.
When comparing products, people should check the ingredients and the percentage of the Nutrient Reference Value (NRV) of the vitamins and minerals in the product to ensure they are comparing like-for-like. For example, while one product may sell at a higher price, it may also include a greater range of different vitamins and minerals, or a higher percentage NRV.