surements greater than 4 SD above normal at baseline in two of the women (Cunningham and Mazess, 1983; Greer and Garn, 1982). Moreover, it is not clear whether the adolescents were randomized to receive intensive counseling and why there were uneven sample sizes in the two groups of lactating adolescents (n = 15 and 21). Due to the small sample sizes and the uncertainties regarding this study, it is not clear whether the calcium AI in lactating adolescents should be higher than the AI of 1,300 mg (32.5 mmol)/day in the nonlactating adolescent.

TOLERABLE UPPER INTAKE LEVELS

Hazard Identification

Calcium is among the most ubiquitous of elements found in the human system. As stated earlier, calcium plays a major role in the metabolism of virtually every cell in the body and interacts with a large number of other nutrients. As a result, disturbances of calcium metabolism give rise to a wide variety of adverse reactions. Disturbances of calcium metabolism, particularly those that are characterized by changes in extracellular ionized calcium concentration, can cause damage in the function and structure of many organs and systems.

Currently, the available data on the adverse effects of excess calcium intake in humans primarily concerns calcium intake from nutrient supplements. Of the many possible adverse effects of excessive calcium intake, the three most widely studied and biologically important are: kidney stone formation (nephrolithiasis), the syndrome of hypercalcemia and renal insufficiency with and without alkalosis (referred to historically as milk-alkali syndrome when associated with a constellation of peptic ulcer treatments), and the interaction of calcium with the absorption of other essential minerals. These are not the only adverse effects associated with excess calcium intake. However, the vast majority of reported effects are related to or result from one of these three conditions.

Nephrolithiasis

Twelve percent of the U.S. population will form a renal stone over their lifetime (Johnson et al., 1979), and it has generally been assumed that nephrolithiasis is, to a large extent, a nutritional disease. Research over the last 40 years has shown that there is a direct relationship between periods of affluence and increased nephroli-



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