DEAR DR. BLONZ: I take vitamins with dinner, along with a 1,000-milligram calcium pill. I had thought this was the best way to get my daily requirements, but now I hear that we only absorb 500 mg at a time. Is that true? How do you recommend getting one's calcium? -- D.T., Phoenix
DEAR D.T.: There is a specific mechanism by which calcium gets absorbed from the digestive tract, and the 500 mg at a time max is a reasonable approach. It turns out that on average, the human body only absorbs about 20 to 30 percent of the calcium it ingests. This can rise to 50 to 60 percent during adolescence, pregnancy and lactation, but these are periods of unusual demand where the body has its absorptive machinery set on "high." All this absorptive inefficiency is taken into account during the setting of calcium dietary requirements for different age groups.
You are probably getting some calcium from your food, but when taken as a supplement, it makes sense to divide it up among two or more meals. Here are some other steps you can take to help increase your absorption of calcium and other minerals.
-- Get adequate amounts of vitamin D. This vitamin is involved in the production of a calcium-binding protein that helps transport calcium through the intestinal wall. Note that your intake of vitamin D doesn't have to be at the same meal as the calcium.
-- Have enough dietary protein, but don't overdo it. An adequate intake of protein is essential, not only because protein is needed for tissue growth and enzyme production, but because calcium tends to form easily absorbed salts with the amino acids in protein. However, excessive intakes of protein can create an acid burden that drains calcium from the body.
-- Lactose can help, as long as you're not intolerant. This carbohydrate found in milk products can enhance calcium uptake. The effect is tied to the activity of lactase, the intestinal enzyme that helps break down the lactose. However, lactose intolerant individuals -- those who don't produce enough of their own enzyme to digest the lactose -- will not realize this particular benefit.
-- Mealtime is best. The acid environment created during digestion helps keep calcium in solution and ready to be absorbed.
-- Keep phytates and oxalates away. Phytic acid, a naturally occurring compound found in the outer hulls of cereal grains, forms an insoluble salt with calcium and other minerals. This doesn't apply to whole-grain breads, as the phytic acid is broken apart during the leavening process. Oxalic acid, found in rhubarb, swiss chard, cocoa and beet greens, also forms an insoluble salt with calcium. If a meal contains any of these foods, make sure that it's not your only calcium-containing meal of the day.
Aside from all these details associated with calcium absorption, it is also important to appreciate that physical activity improves bone mineralization. Staying active helps to keep that calcium in your bones where you want it.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.