Remember that this is unedited text -- like "letters to the editor." Identifying information, such as names, has been removed; but otherwise it is posted here pretty much as it came in. So read it as personal opinion shared with warm intentions but without authority of any kind.
Notes and quotes from: Griffin, IJ; Abrams, SA. Iron and Breastfeeding. The Pediatric clinics of North America, 48:2 (Apr 2001), 401-413.
The nutritional objective must be optimal iron levels. Insufficient iron can lead to iron deficiency anemia. Excess iron may actually contribute to the growth of certain microbes. In adults, excess iron may contribute to the growth of malignant cells, but whether this is true in children is unknown. Excess iron seems more likely to be a problem when it is injected than in dietary form. (p. 404)
There is much variability between mothers in breast milk iron levels, and even within the same mother from one time to the next. However, the "iron content of human milk does not seem to be affected significantly by the morther's iron status, maternal iron deficiency, or maternal iron therapy." (p.404)
"Initially iron fortification was achieved by the adition of iron salts, often of low bioavailability, to the food. The change to small-particle electrolytic iron has improved greatly the bioavailability of iron from infants' cereals, and vitamin C has been shown to further increase iron bioavailability. For example, consuming iron-fortified weaning foods with a vitamin C-rich drink leads to a twofold increase in iron absorption." (p. 405)
[From the studies cited in the article], "human milk-feeding seems to be adequate to prevent iron-deficiency anemia during the first 6 months of life, and possibly much longer. After 6 months of age, the introduction of iron-fortified cereals may support normal iron status. After exclusive breastfeeding is stopped, iron-fortified formulas and cereals should be introduced. The use of non-iron-fortified formulas and cereals after exclusive breastfeeding increases the risk for iron deficiency." (p. 408)
"Despite much research, there are many areas of uncertainty regarding iron supplementation of infants, including that:
1. The optimal age for introducing iron-fortified supplemental foods is poorly defined and should be further evaluated.
2. The natural history of iron deficiency and iron-deficiency anemia during the first year of life is unclear, as are the possible long-term effects of this,
especially on developmental outcome.
3. The biologic variability among infants and among their mothers that allows many infants who do not receive iron-fortified foods to prevent iron deficiency
while receiving only muman milk throughout the first year of life is intriguing and warrants additional study.
4. The iron requirements of small-for-gestational-age, term infants are unknown. Their iron requirements are likely to be higher than those of average term infants, but whether iron suplements are required is unclear.
5. The optimum amount of dietary iron in the weaning diet needs to be further defined. Similarly, the optimal source and amount of iron in infant formalas
given to infants who receive a mixture of human milk and formula is unclear." (p. 409-10)
During pregnancy and lactation there seem to be physiological changes in calcium and bone metabolism that make calcium available for the fetus and for breast-milk production without increase in calcium intake. Calcium absorption increases in pregnancy. During lactation, excretion of calcium decreases, and calcium is temporarily drawn from the bones.
Increased calcium intake during lactation doesn't change these processes, even in women with low calcium intake. There is less research for the following, but some evidence suggests that the same may be true during pregnancy, although low calcium intake during pregnancy may carry some risks.
For mothers with moderate-to-high calcium status, increased calcium intake carries some risk of kidney stones and urinary tract infections and may also reduce absorption of minerals such as iron and zinc. (Prentice, A, Calcium in pregnancy and lactation, Annual Review of Nutrition 20 (2000) 249-72)