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Calcium chaos

Posted Aug 25 2008 3:03pm 1 Comment

Imagine that I'm planning to build a wall of bricks. I start by throwing cement at a pile of bricks, hoping that it forms a nice, orderly brick wall.

Fat chance, you say.

I believe that is what appears to be emerging as the situation with calcium supplementation.

A recent study from New Zealand reported an experience with 1,471 postmenopausal women, mean age of 74 years, who were randomized to treatment with either calcium supplements or placebo. Calcium was supplied as calcium citrate (Citrical) to provide 1000 mg of (elemental) calcium per day (400 mg morning, 600 mg evening).

(Bolland MJ, Barber PA, Doughty RN et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. Brit Med J BMJ, doi:10.1136/bmj.39440.525752.BE; published 15 January 2008)

Over 5 years, women taking calcium had twice the risk of having a heart attack compared with women taking the placebo; women taking calcium had a 47 percent higher risk of having any one of three "events" (heart attack, stroke or sudden death) than women in the placebo group.

The findings of this study run counter to what we've been telling people all these years: Calcium supplementation, usually taken to halt deteriorating bone health and osteoporosis, modestly reduces blood pressure, reduces LDL and raises HDL cholesterol. At first blush, we might thereby presume that it also reduces cardiovascular events.

This study suggests that calcium supplementation does not result in reduction of cardiovascular events, perhaps even increases risk.

Certainly, this new finding will serve to confuse the public even more than it is already, particularly when it comes to strategies that modify risk for heart attack. However, this may make more sense once we stop and think for a moment.

Calcium supplementation inarguably slows, occasionally halts, calcium resorption from bone (through suppression of parathyroid hormone). Calcium also accumulates as part of atherosclerotic plaque in coronary and other arteries.

How does oral calcium know where to go--bones, not arteries or kidneys, in addition to serving all its other crucial functions?

Keep in mind that, in many roles, calcium is passive, something that responds to control exerted by some other factor. Vitamin D is that factor. Vitamin D controls the absorption of calcium in the intestinal tract (calcium aborption quadruples when vitamin D is restored to normal), it controls whether calcium is deposited in bone or extracted from arteries. It is the master control over the fate of calcium. Calcium just goes along for the ride.

Bone and arterial health do indeed intersect via calcium, but not through calcium supplementation. Instead, the control exerted by vitamin D (and vitamin K2, another conversation) connects the seemingly unrelated processes.

At what calcium dose threshold do the benefits stop and the adverse effects begin? That remains unanswered, particularly in light of this new study. However, this study calls into serious question the wisdom of supplementing calcium at a dose of 1000 mg, particularly when taken without normalization of vitamin D.

Calcium is therefore emerging as an important player in artery health. But just taking calcium makes no more sense than our brick wall and cement analogy. You might regard vitamin D as the mason that skillfully lays down both brick and cement in a neat, orderly way.

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