Fortified foods provide an alternative source of nutrients for people who don't consume enough of the foods that naturally supply those nutrients. Like supplements, fortified foods offer insurance against the health problems associated with nutritional deficiencies. The types of foods that are fortified with additional nutrients are usually those that are more commonly consumed by large numbers of people.
For instance, salt is fortified with the essential mineral iodine, because it is a product commonly used by most people and iodine is otherwise difficult to get in necessary quantities through an average American's diet. At the same time, many brands of fruit juices are now fortified with calcium for those children and adults who don't drink enough milk or consume enough dairy products to meet their requirements from these natural sources.
Back in the 1920s and 1930s, certain vitamin and mineral deficiencies were prevalent in the United States, and the food fortification program established by the government in cooperation with food manufacturers was initiated to help prevent the diseases that resulted from these deficiencies. Salt was fortified with iodine to prevent a thyroid condition known as goiter, and milk was fortified with vitamin D to prevent a bone disease known as rickets, which was affecting many children. Soon after, flour and breads were enriched with the B vitamins thiamin, riboflavin and niacin, plus iron, nutrients that are naturally found in grains. More recently, grain and cereal products were fortified with additional folate, a B vitamin, as insurance against the development of neural tube birth defects. All of these fortification programs have been successful at reducing nutritional deficiencies and also reducing the incidence of related health problems.
Fortified vs. Natural
There is one important reason why it's better to get your nutrients naturally from foods, whenever possible, rather than from fortified products or supplements, unless prescribed for medical reasons. If you eat a normal, balanced, varied diet, it is all but impossible to get too much of any nutrient from food alone. But consume enough fortified foods every day, and you could easily top the upper limits established by government nutritionists, especially if you are also taking dietary supplements.
Although rare, nutrient overdose is possible and can lead to illness or even death. A study performed by the Centers for Disease Control and published in a 1995 issue of the American Journal of Public Health, found that out of 56 people who consumed too much vitamin D from over-fortified milk produced in a local dairy, 41 were hospitalized with illness and two people died. Other factors, such as use of vitamin D supplements and pre-existing medical conditions, increased the risk of illness for some of the study participants, but all had side effects specifically related to the over-fortification of the milk they were drinking.
Although fortification of foods is not mandatory, an abundance of foods now contain added nutrients and many consumers seek out products that promise to provide extra nutrition. Over the years since the 1970's, government agencies have even sought to limit the number of fortified products available on the market. Although there are no regulations in place, the Food and Drug Administration encourages food manufacturers to follow published guidelines and policies when fortifying their products to prevent unacceptably high intakes of some vitamins and minerals. It is up to you, the consumer, to use fortified products (and supplements) with discretion.
Sources:
Blank S, et al. "An Outbreak of Hypervitaminosis D Associated with the Overfortification of Milk from a Home Delivery Dairy." American Journal of Public Health. May 1995;85(5):656-9. Web. 17 June 2011
Harvard School of Public Health: Keep the Multi, Skip the Heavily Fortified Foods. Web. 17 June 2011
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/folic-acid/
Dietary Reference Intakes: Guiding Principles for Nutrition Labeling and Fortification. National Academies Press, 2003. Web 17 June 2011
http://www.nap.edu/openbook.php?record_id=10872&page=45
