(USDA) since 1909 (see Table 3-3). These data do not represent actual consumption, however, since they fail to document how much food was wasted. Per-capita calcium availability in the food supply increased 23% from 750 mg/day during 1909-1913 to 920 mg/day in 1985 (see Table 3-3). The change resulted primarily from an increased supply of dairy products during this period. The per-capita availability of phosphorus in the food supply has remained fairly steady at 1,500 mg/day since 1909-1913, and that of magnesium has declined from 380 mg/day during 1909-1913 to 320 mg/day in 1985 (see Table 3-3). The decline resulted primarily from the decreased use of grains and flour and increased practice of low-extraction milling.
Information on current intakes of calcium, phosphorus, and magnesium has been collected in national surveys, including the 1977-1978 Nationwide Food Consumption Survey (USDA, 1984), the second National Health and Nutrition Examination Survey (Carroll et al., 1983), the Continuing Survey of Food Intakes of Individuals (USDA, 1986, 1987), and the Total Diet Study (Pennington et al., 1986) (see Chapter 3). In USDA surveys, calcium intakes have been reported in terms of the 1980 Recommended Dietary Allowance (RDA), which is highest (1,200 mg) at ages 11 to 18 years and is only 800 mg for ages 1 to 10 and 18 and above (NRC, 1980). Mean intakes below the RDA do not necessarily mean that individuals in the group are malnourished. Nutrient requirements differ from individual to individual, and the RDAs are set at high enough levels to cover the requirements of practically all healthy people in the population. Furthermore, these nationwide surveys do not reflect the usual or habitual intakes of individuals. It is inappropriate, therefore, to conclude that failure to meet the RDA indicates that an individual has an inadequate calcium intake, although the risk that some people will have inadequate intakes increases as the mean intake falls further below the RDA. Percentages of the RDA are reported here only to indicate relative intakes on the days surveyed.
Mean intakes of calcium are lower for females than for males and lower for blacks than for whites. USDA surveys indicate that females ages 9 to 19 had somewhat higher intakes in 1965 than during 1977-1978, but that older women (51 to 75 years of age) had higher intakes during 1977-1978 than in 1965 (Figure 13-1) (USDA, 1984). Mean intakes for women 19 to 50 years old were higher in 1985 than in the previous surveys (USDA, 1987).
The 1985 survey indicated that 22% of women ages 19 to 50 consumed the RDA or more, 24% consumed between 70 and 99%, 26% consumed between 50 and 69%, and 29% consumed less than 50% of the RDA. The mean intake for black women