"Are Calcium Supplements Safe?"
In 12 short years, government panels have gone from suggesting widespread
calcium supplementation may be necessary to protect our bones to
"Do Not Supplement." What happened?
It all started with a 2008 study in New Zealand.
Short-term studies had showed that calcium supplementation may drop
blood pressures by about a point, though the effect appears transient,
disappearing after a few months, but it's better than nothing.
And excess calcium in the gut can cause fat malabsorption,
by forming soap fat, reducing saturated fat absorption
and increasing fecal saturated fat content.
And indeed if you take eat a couple Tums along with your half bucket of KFC,
up to twice as much fat could end up in your stool.
And with less saturated fat absorbed in your system your cholesterol might drop.
So the New Zealand researchers were expecting to lower heart attack rates
by giving women calcium supplements.
To their surprise there appeared to be more heart attacks
in the calcium supplement group. Was this just a fluke?
All eyes turned to the Women's Health Initiative, the largest and
longest randomized controlled trial of calcium supplementation.
The name might sound familiar. That's the study that uncovered
how dangerous hormone replacement therapy was.
Would it do the same for calcium supplements?
The Women's Health Initiative reported no adverse effects.
However, the majority of the participants
were already taking calcium supplements before the study started,
so effectively the study was just comparing higher versus
lower dose calcium supplementation,
not calcium supplements versus no calcium supplements.
But what if you go back and just see what happened to the women
who started out not taking supplements and then were randomized
to the supplement group?
Those who started calcium supplements suffered significantly
more heart attacks or strokes.
Thus, high dose or low dose, any calcium supplementation seems
to increase cardiovascular disease risk.
So researchers went back digging through other trial data for heart attack
and stroke rates in women randomized to calcium supplements,
with or without vitamin D added, and confirmed the danger.
And most of the population studies agreed:
users of calcium supplements tended to have increased rates
of heart disease, stroke, and death.
The supplement industry was not happy,
accusing the researchers of relying in part
on self-reported data -- like they just ask if people had a heart attack or not
rather than verifying it.
And indeed long-term calcium supplementation
causes all sorts of gastrointestinal distress
including twice the risk of being hospitalized with acute symptoms
that may have been confused with a heart attack.
But no, the increased risk was seen consistently
across the trials whether the heart attacks were verified or not.
OK, but why do calcium supplements increase heart attack risk,
but not calcium you get in your diet?
Perhaps because when you take calcium pills,
you get a spike of calcium in your bloodstream
that you don't get just eating calcium rich foods.
Within hours of taking supplemental calcium, the calcium levels
in the blood shoot up and can stay up as long as eight hours.
This evidently produces what's called a hypercoaguable state -- your blood clots
more easily -- which could increase the risk of clots in the heart and brain.
And indeed higher calcium blood levels
are tied to higher heart attack and stroke rates.
So the mechanism may be calcium supplements
leading to unnaturally large, rapid, and sustained calcium levels in the blood,
which can have a variety of potentially problematic effects.
Calcium supplements have been widely embraced on the grounds that
they are a natural and therefore a safe way of preventing osteoporotic fractures.
But it's now becoming clear that taking calcium in one or two daily doses
is not natural, in that it does not reproduce the same metabolic effects
as calcium in food -- the way nature intended.
And furthermore the evidence is also becoming steadily stronger
that calcium supplementation may not be safe.
That's why most organizations providing advice regarding bone health
now recommend that individuals should obtain their calcium requirement
from diet in preference to supplements.
But if we can't reach it through diet alone, would the benefits to the bones
outweigh the risks to the heart? We'll find out, next.