Adams: In your book you talk about the link with calcium and calcium assimilation. How important is that for people to understand?
Dr. Holick: Well, it's critically important for people to realize that even if they have an adequate amount of vitamin D, if they don't have any calcium around, the vitamin D can't have the desired effect on bone health without being able to get enough calcium out of the diet and to put it into the bloodstream which will eventually get to your bones. So, making sure that you have adequate calcium intake is very important. And the recommendation by the Institute of Medicine (and I was on this committee back in 1997) is that if you're a teenager, 1300mg a day of calcium, for adults ages 18-50 it's 1000mg of calcium and 51+ years it's 1200mgs of calcium for both men and women.
Adams: And you mention that you have to have calcium in your system for vitamin D to work - is the opposite also true? You've got to have vitamin D for the calcium to be effective?
Dr. Holick: Oh, no question about it. If you are deficient in vitamin D, you absorb on average 10-15% of the calcium that's in your diet. If you’re sufficient in vitamin D, if you have adequate sun exposure or adequate intake of vitamin D, you absorb about 30% of the calcium in your diet. During pregnancy and lactation, and during growth spurts, the body responds appropriately by actually increasing that efficiency up to 80%.
Adams: So the normal level is 30%.
Dr. Holick: 30% for healthy adults, yes.
Adams: So a person who's taking, let's say coral calcium supplements, if they're not getting sunshine or vitamin D to go with it, their absorption is halved.
Dr. Holick: Yeah, exactly, and it's really of little benefit.
Adams: That's fascinating. Once again showing that there's no single magic pill, you have to be healthy across the board.
Dr. Holick: That's right. And what I typically recommend to my patients is Tums or Os-Cal or Caltrate or any of the respected brands ... Super Cal or all good sources of calcium.
Adams: As long as you've got vitamin D.
Dr. Holick: Correct. If you have adequate vitamin D or some sun exposure.
Adams: Cod liver oil is of course a great source of vitamin D, as you mention, but some people are concerned about contamination of these oily fish with heavy metals - is that a concern?
Dr. Holick: Yes, PCBs. And so, what you have to do is if you're going to buy it, buy it from a respectable source. Certainly it's a step in the right direction. But you know there are omega fatty acids in there that have benefits to the heart, and have other health benefits. So it may be that many of those outweigh the possible risk if there are contaminants in there. Although, like I said, a lot of the manufacturers are pretty good at making sure that there aren't.