Calcium Confusion From the WHI

In yet another media “bombshell” from the Women’s Health Initiative and the New England Journal, we are now being told that calcium isn’t as good as we thought in preventing fractures. (See study here.) Moreover, women who take calcium supplements have higher rates of kidney stones than women who don’t. And once again, the media is off and running…

No problem. I can handle this one with my hands tied behind my back…aiebpqiwuy756435yh 46ty2w4… Oh, sorry, I forgot that I can’t type with my nose. Let me get my other shoe off, I’ll use my toes. Okay, are you ready? ‘Cause here we go…

First, let’s talk about the intervention studied by the WHI : Approximately 36,300 women nationwide were randomly assigned to placebo or 1000 mg/day elemental calcium combined with 400 IUs/day of vitamin D. The primary outcome was osteoporotic hip and other bone fractures, with colon cancer as a major secondary outcome. Overall, women assigned to take calcium supplements had no less osteoporotic fractures than those taking placebos.

What???? Oh, wait. I understand. When they looked at women who actually took the pills as advised, there was a 29% reduction in fractures.

So, what they seem to be saying is this – telling women to take calcium and vitamin D doesn’t prevent fractures. Sort of like telling my kids to brush their teeth to prevent cavities – it only works if they actually do it. OK, I’ll buy that.

The statisticians don’t like to hear this. They prefer the purity of an intent to treat analysis, where the only valid comparison is what goup study participants were assigned to, not what they actually did. As a clinician, I alswys have trouble with intent to treat analysis – I tend to want to drill down and find out why. I would argue that this is as valid as the intent to treat.

A benefit was also seen to calcium supplementation in the over-60-years-old crowd. Gee, that makes sense too. I wouldn’t expect to see a big difference in fractures in the under 60 crowd, because that group doesn’t get many fractures. And if someone in that age group is breaking her hip, I’d have a strong suspicion there’s something else going on other than just age. Like maybe anorexia or smoking or an overactive parathyroid gland or malabsorption, to name a few possibilities. No amount of calcium is going to fix that. Hmm…So far, it sounds like calcium is doing exactly what I’d expect it to do.

But that’s not what CBS News says. Their headline? “Calcium, Vitamin D Assumptions Shaken.” Why? Because the big groups analysis showed no benefit to calcium, that’s why. And do you know why? Because the women who received placebo were allowed to take calcium and vitamin D supplements on their own! That’s right. Here it is, right out of the WHI press release: “Since participants were not restricted from taking personal calcium or vitamin D supplements, they had a relatively high calcium and vitamin D intake at enrollment and intake rose even higher during the trial so the impact of study supplementation may have been muted.”

What the researchers are telling you is that since they didn’t control the very intervention they were studying, their results might not be right.

Oh, and one more confounding issue. They also did not restrict the use of Fosamax-type drugs in either group, so about 15% of women ended up on these fracture-preventing meds during the course of the study. This means that most likely the women at risk for fractures in both groups were already taking a more effective medication than just calcium and vitamin D.

Are you getting all this?

Now, let’s talk some more about the WHI’s intervention – namely, giving all women the same dose of calcium, regardless of what amounts they may have been getting in their diet.

You know what? This is not the way we doctors recommend that women take calcium.

Here’s the recommendation of the National Osteoporois Foundation and the American College of Obstetricians and Gynecolgists: “Food is the best source of calcium; however, most Americans do not have enough calcium in their diets. Fortunately, calcium-fortified foods and calcium supplements can fill the gap, ensuring that the daily calcium requirement is met. The amount needed from a supplement depends on how much calcium is consumed from food sources.”

Hmm…I don’t see any recommendation that every woman be given 1000 mg of calium as a supplement daily. Gee, I wonder what might happen if women were to take calcium supplements without taking into account their dietary sources? Maybe they’ll get too much calcium. And what can too much calcium cause? (Let’s shout it out together, shall we?) KIDNEY STONES!

Oh, wait, wait… I forgot to tell you about the vitamin D dose studied – 400 IU daily. Unfortunately, it’s too low. The current recommendation is 800 IU daily. (And not 600 IU as the NY Times says.)

Mrs. O’Leary Milking Daisy by Norman Rockwell
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Comment : define_me
February 16, 2006
Maybe I should aim to get my first publication with the New England Journal of Medicine…hehehe

Comment: Anonymous
February 17, 2006
Between the calcium and fat study, the headlines should read: Impossible to do prospective food study; massive waste of money and time. Conclusion: retrospective food studies, or even large population studies (Japanese on traditional diet v. American diet) are clearly the best information we’ll get—and far cheaper.) I’m not even going to think how many children could be fed and vaccinated, or how much prenatal nutrition could be paid for with the 415 million from the fat study…

Comment: Guinness_Girl
February 17, 2006
That’s all I have to say. Wow