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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
(1966a, 1966b) were used for all calculations in adolescent and adult females. This data set was selected for the following reasons:
It is representative of the other survey data quoted above and can be considered generalizable to women living in countries other than that of the study, including the United States and Canada.
Women were selected to fall into six age groups between 15 and 50 years, thus permitting estimates for all women.
Although the original data were not available, comprehensive descriptions of the distribution of menstrual losses are available from a series of publications by Hallberg and colleagues.
The survey was carried out before intrauterine devices and oral contraceptives were widely available. Only one woman in the study was using an oral contraceptive. None of them used an intrauterine device. The measurement can therefore reasonably be assumed to reflect “usual losses”.
Blood losses per menstrual cycle were converted into estimated daily iron losses averaged over the whole menstrual cycle. The following assumptions were made:
Blood loss does not change with mild anemia and is therefore independent of hemoglobin concentration.
In estimating hemoglobin loss (blood loss × hemoglobin concentration), hemoglobin concentration was taken as a constant (135 ± 9 g/L in adult women and based on age in adolescents) (Hallberg and Rossander-Hulthen, 1991) and variance was ignored.
The iron content of hemoglobin is 3.39 mg/g (Smith and Rios, 1974).
The duration of the average menstrual cycle is 28 days. Beaton and coworkers (1970) reported a cycle duration of 27.8 ± 3.6 days in 86 self-selected healthy volunteers.
Since the distribution of menstrual blood losses in the data reported by Hallberg is skewed, it was modeled as described previously (see “Selection of Indicators for Estimating the Requirement for Iron—Factorial Modeling”). Comparison of the observed and modeled values (Table 9-12) provides a way of visualizing the adequacy of the fit of the model. A log-normal distribution was fitted to the reported percentiles of the blood loss distribution (natural log of blood loss = 3.3183 ± 0.6662 [SD]) to result in a median blood loss of 27.6 mL/estrous cycle. Blood losses of greater than 100 mL/ estrous cycle are observed at the ninety-fifth percentile (Table 9-12)
