DEAR DR. BLONZ: I wanted to ask a few questions about calcium. Have you heard anything about the absorbability or bioavailability of calcium hydroxyapatite? I have heard arguments that it is the most available because it is a component itself of bone matter. What do you think? I have also heard that milk is not the best source of calcium for bones because of all its protein. What is that about? -- S.P., Phoenix, Arizona
DEAR S.P.: Calcium hydroxyapatite is the main calcium compound found in bones. Because it is bone, it contains the full complement of “on the job” bone minerals. Somewhere along the line, someone came up with the idea that it would be an ideal calcium supplement; just grind up cow bones, and there you have it. We must consider that calcium must be absorbed before it can be utilized for its many biological purposes, which, of course, includes the making of bones. Hydroxyapatite has yet to demonstrate any superiority as a calcium supplement. If higher absorption is the key, the best bets are calcium citrate malate or calcium citrate.
The bottom line here is that it is more important to get the calcium than spend too much time worrying over which form is best. Regardless of which form you take, it is accepted that mealtime is the best time to take calcium. But there has been some controversy about the issue of calcium supplements, so check out the article at b.link/calcium63.
You mention the issues of milk and protein, and the impact on our bones. The impact of protein on bones is complicated. Milk itself is not the issue here. The key fact is that excess protein is not stored in the body. Rather, it is converted into energy, which the body can and does store, perhaps more efficiently than some of us might appreciate.
Changing protein into energy creates a bit of metabolic refuse, and this needs to be eliminated from the body through the kidneys. That refuse has a negative charge, and animal proteins tend to create more of the negatively charged compounds. The kidneys have to pair this refuse with a positively charged escort for it to exit the body. While not the body’s first choice, calcium, a positively charged ion, can serve this purpose. Other positively charged substances to serve this purpose are found in fruits and vegetables. But if little else is around, there is always calcium in the blood, and it can get the call. The level of calcium in the blood needs to be maintained, so if calcium ends up on escort duty, more calcium gets pulled from the bones to maintain the blood level.
To summarize, some calcium can be lost when one eats a high-protein diet, but this will be more of an issue with a diet that does not contain the recommended intake of fruits and vegetables. Yet another reason for that plant-based, whole foods diet.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.