The Recommended Nutrient Intakes for Iron...continued.

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

16. Hallberg, L. 1966. Menstrual blood loss - a population study. Variation at different ages

and attempts to define normality. Acta. Obstet. Gynecol. Scand., 45: 320-351.

Menstrual blood losses are very constant from month to month for an individual butvary markedly from one woman to another (16).

17. Rybo, G-M. & Hallberg, L. 1966. Influence of heredity and environment on normal menstrual blood loss. A study of twins. Acta. Obstet. Gynecol. Scand., 45: 389-410.

18. Rybo, G-M. 1966. Plasminogen activators in the endometrium. I. Methodological aspects and II. Clinical aspects. Acta. Obstet. Gynecol. Scand., 45: 411-450.

The main part of this variation is genetically controlled by the content of fibrinolytic activators in the uterine mucosa even in populations which are geographically widely separated (Burma, Canada, China, Egypt, England, and Sweden) (17, 18).

These findings strongly suggest that the main source of variation in iron status in different populations is not related to a variation in iron requirements but to a variation in the absorption of iron from the diets. (This statement disregards infestations with hookworms and other parasites.) 

The mean menstrual iron loss, averaged over the entire menstrual cycle of 28 days, is about 0.56 mg/day. The frequency distribution of physiologic menstrual blood losses is highly skewed. Adding the average basal iron loss (0.8 mg ) and its variation allows the distribution of the total iron requirements in adult women to be calculated as the convolution of the distributions of menstrual and basal iron losses (Figure 23).

19. Hallberg, L. & Rossander-Hulthénm, L. 1991. Iron requirements in menstruating women. Am. J. Clin. Nutr., 54: 1047-1058.

The mean daily total iron requirement is 1.36 mg. In 10 percent of women it exceeds 2.27 mg and in 5 percent it exceeds 2.84 mg (19). In 10 percent of menstruating (still-growing) teenagers, the corresponding daily total iron requirement exceeds 2.65 mg, and in 5 percent of the girls it exceeds 3.2 mg/day. The marked skewness of menstrual losses is a great nutritional problem because personal assessment of the losses is unreliable. 

This means that women with physiologic but heavy losses cannot be identified and reached by iron supplementation. The choice of contraceptive method greatly influences menstrual losses. The methods of calculating iron requirements in women and their variation were recently re-examined (19). 

In postmenopausal women and in physically active elderly people, the iron requirements per unit of body weight are the same as in men. When physical activitydecreases as a result of ageing, blood volume and haemoglobin mass also diminish, leading to a shift of iron from haemoglobin and muscle to iron stores. 

This implies a reduction of the daily iron requirements. Iron deficiency in the elderly is therefore seldom of nutritional origin but is usually caused by pathologic iron losses. The absorbed iron requirements in different groups are given in Table 39.