average of 61 mg [2 mmol]/day or 5 percent of the total intake) when intakes were calculated using USDA's nutrient database (Pennington and Wilson, 1990).
Because of the uncertainty about phosphorus values for processed foods in nutrient databases, trends in phosphorus intake may be difficult to ascertain. Daily intakes of women aged 19 to 50 years from USDA 's national surveys averaged 965 mg (31.1 mmol) in 1977, 1,039 mg (33.5 mmol) in 1985, and 1,022 mg (33.0 mmol) in 1994 (Cleveland et al., 1996; USDA, 1985). Thus, it appears that intakes from foods increased about 8 percent between 1977 and 1985, but then decreased slightly between 1985 and 1994. Food supply data show a larger increase in phosphorus consumption: 12 percent from 1980 through 1994 (from 1,480 to 1,680 mg [47.7 to 54.2 mmol]/day per capita) (USDA, 1997). However, disappearance data may be unreliable for detecting trends because phosphate additives (such as those in cola beverages) are not included. Disappearance data on phosphorus-containing additives show that the use of these additives has increased by 17 percent over the last decade (Calvo, 1993). These figures also do not reflect actual consumption, because not all phosphates included in disappearance data are actually consumed, (for example, blends of sodium tripolyphosphate and sodium hexametaphosphate are used in brines for curing meat, but the brine is rinsed off and not consumed). Nevertheless, taken together, these data suggest a substantial increase in phosphorus consumption, in the range of 10 to 15 percent, over the past 20 years.
Phosphates are found in foods as naturally occurring components of biological molecules and as food additives in the form of various phosphate salts. These salts are used in processed foods for nonnutrient functions, such as moisture retention, smoothness, and binding.
In infants, dietary intake of phosphorus spans a wide range, depending on whether the food is human milk, cow milk, adapted cow milk formula, or soy formula (see Table 5-2). Moreover, the phosphorus concentration of human milk declines with progressing lactation, especially between 4 and 25 weeks of lactation (Atkinson et al., 1995). By contrast, more of the variation in dietary intake of phosphorus in adults is due to differences in total food intake and less to differences in food composition. Phosphorus contents of adult diets average about 62 mg (2 mmol)/100 kcal in both sexes (Carroll et al., 1983), and phosphorus:energy ratios exhibit a coefficient of variation of only