Food additives, including colourants, flavour enhancers, sweeteners, emulsifiers, and preservatives, are substances that are added to foods to preserve them or to enhance their taste and appearance. A food additive may have nutritional value but is not normally consumed as a food by itself. Generally not considered to be food additives are herbs, spices and substances such as micronutrients (for example iron or vitamin B12) that are added solely to improve a food’s nutritional qualities. Many food additives have a long history and are derived from food ingredients or non-food substances that have traditionally been used for processing foods (e.g. chalk or beetroot juice colourant). Others are produced using chemical synthesis (e.g. aspartame and synthetic vitamins). Some question the health impacts of certain additives from this latter group. Many national and international health authorities regulate additives by banning their use and by defining intake limits.