Question: You have mentioned that water hardness can affect the natural pigments in food and result in color changes. Can you explain what is meant by water hardness?
Answer: Hard water is simply water that contains natural salts. There are two types of hard water. In one, called "temporarily hard," the calcium, magnesium and iron bicarbonate are precipitated when water is boiled. Over a long period of time, deposits of these mineral salts build up. They are likely to be found in a kettle used exclusively for boiling water. The second type, "permanently hard" water, contains calcium, magnesium and iron sulfates that do not precipitate on boiling. But they do form insoluble compounds with soaps, making them less effective cleaning agents.
Some people who live in hard-water areas decide to install water-softening systems to remove these minerals. One type of water softener involves the exchange of these mineral ions for sodium ions. The result is a water supply that can be quite high in sodium.
Q: Does adding chocolate to milk decrease the absorption of calcium from the milk?
A: The idea that the oxalate in chocolate will tie up the calcium in milk refuses to die. That hypothesis was disproved more than 40 years ago in animal studies in which substantial amounts of low-grade cocoa given together with milk did not affect the utilization of calcium in the milk.
In studies conducted a number of years later, college students were fed enough chocolate to cause cramps and nausea, but calcium utilization was still not affected. Moreover, the oxalate content of the cocoa used in that study was higher than would occur in most of the cocoa used in foods for human consumption.
Q: I have been advised by my pediatrician to give my young son an iron supplement. But recently I read that too much iron can interfere with zinc absorption. I began to wonder: Are supplements really safe for young children?
A: According to the latest findings of a group of researchers led by Dr. Peter Dallman of UC San Francisco, iron supplements do not compromise zinc status, a least when given apart from meals, as they were in that study.
The investigators evaluated the iron status as well as the serum zinc and copper levels of a group of 291 1-year-olds, who were then divided into two groups. Half were given an iron supplement to be taken 30 minutes before breakfast, and the rest were given a placebo, or sugar pill. At the end of three months, blood tests were repeated. Although some measures of iron status improved as expected, serum zinc and copper levels did not change.
The researchers offer several explanations for their findings, which seem to differ from previous reports of adverse effects of iron supplements on zinc absorption. First, in one earlier study in which iron was found to affect zinc absorption negatively, subjects were given doses of both minerals at the same time. Indeed, in most studies of the suppression of absorption of one mineral or another, both are given at the same time. Immediate changes in serum-zinc levels may not be reflective of a consistent effect on zinc retention.
In adults, it has been shown that whereas zinc absorption is depressed under fasting conditions, this does not occur if the two minerals are given with a meal, or when zinc is given in a form where it is tied to a so-called "dietary ligand," or binding agent. (This phenomenon has not yet been studied in infants.)
Thus, the question of whether iron supplements taken with meals or giving iron without other minerals could jeopardize zinc nutrition, especially in infants who are not well nourished, remains to be investigated. This study does provide reassurance that a common mode of iron supplementation in infants does not compromise either their zinc or copper nutrition.