Saturday, April 23, 2011

Calcium Supplements Found (Again) To Increase Risk For Heart Attack, Stroke

The leading cause of death for women in America is heart disease.1 It now looks like some of those heart attacks (and strokes) may have been provoked by the calcium supplements women were taking to protect their bones. (Heart disease is the leading cause of death in men too, but I don't think men are pressured as much as women to take calcium. Men may also be refraining because of the spectacular association between calcium and prostate cancer.)

A revisit of data in the huge Women’s Health Initiative (WHI) study found that women who took calcium supplements increased their risk for heart attack and stroke:

Calcium Supplements With Or Without Vitamin D And Risk Of Cardiovascular Events: Reanalysis Of The Women’s Health Initiative Limited Access Dataset And Meta-Analysis, British Medical Journal, April 2011

The original WHI analysis showed no such risk. But that was because thousands of women who were already taking calcium before the study weren't told to stop. If those calcium-takers ended up in the placebo group (which was supposed to receive no calcium), you might expect them to show similar heart attack risk as intervention groups (which did receive calcium). That's exactly what they found.

This new analysis looked at women who weren't taking calcium before the study. If those women were randomized to a group that received calcium, it did indeed increase their risk for heart attack and stroke.

The Amount Of Calcium Didn't Matter

Here's Dr. Ian Reid, senior author of the new analysis:
"It is actually taking a supplement that matters, not how much of it you take, that causes this increase in heart risk."
And from a HeartWire interview:
"That makes sense, [Reid] says, since even small levels of supplemental calcium create "abrupt" increases in blood calcium levels within hours. This speaks to one criticism levied at the group's earlier work—namely, that the cardiovascular events seemed to be occurring too swiftly to be related to calcified plaques.
MI spikes likely reflect a more acute response to blood calcium levels, including changes in platelet function, blood coaguability, or endothelial cell activity."
- Calcium Supplements And Cardiovascular Events: New Data, More Debate, HeartWire, April 19, 2011
I would like to add to those mechanisms something readers of this blog already know - calcium lowers vitamin D levels, and vitamin D is thought to be cardio-protective:
"If serum levels of calcium are high, production of 1, 25 D is suppressed by reduced parathyroid hormone production."
- Dairy Products, Calcium, and Vitamin D and Risk of Prostate Cancer, Epidemiologic Reviews, 2001
The present analysis found no benefit in taking vitamin D.

Dr. Reid:
"Our own recommendation is to critically review the use of calcium supplements, since the data in this paper suggests that they do more harm than good."
Women Taking Calcium Supplements May Risk Heart Health, Researchers Say, HealthDay, April 19, 2011
1 CDC: Leading Causes of Death in Females, United States, 2006
That's a photo of the pills I used to take, be still my heart.  Wait.


Laurie Endicott Thomas said...

No illnesses have ever been linked to dietary calcium deficiency. What's worse, dietary calcium excess is actually a risk factor for osteoporosis. This has been known for decades. Yet nearly every postmenopausal woman I know is taking calcium supplements.

Why, oh why, don't people read the scientific literature on nutrition?

woly said...

It seems strange to think that supplemental calcium at *any* dose can be harmful. If I take a 250mg calcium supplement, how would the spike in serum calcium be different than if I drank a glass of milk(containing aproximately the same amount of calcium)? are we to infer that any high calcium source is harmful?

Bix said...

It was a strong statement, wasn't it. I saw it as a risk statement, a population statement, not something that applies to an individual.

I can imagine individual risk would depend on lots of variables ... the state of one's arteries, kidney, liver (and so, probably age), the other foods in a diet, how bioavailable the calcium is, etc.

Hegsted makes a great case for not supplementing.

Doug said...

I've read a couple excellent posts explaining this calcium-heart attack link in Dr. Know's blog... very highly recommended reads:

Laurie Endicott Thomas said...

The main risk factor for myocardial infarction is total cholesterol level. If your total cholesterol is under 150 mg/dL, your arteries become self-cleaning.

Here's a web page that you can use to calculate your risk of having a heart attack in the next 10 years.

It didn't work for me. My total cholesterol level is so low that it causes an error message. You have to enter a value of at least 130 mg/dL.

Sara said...

" The main risk factor for myocardial infarction is total cholesterol level. If your total cholesterol is under 150 mg/dL, your arteries become self-cleaning."

Add that one to the 27 other theories on heart attacks.

Bix said...

Laurie, did you always have low cholesterol? Or has your diet lowered it? (I'm guessing that would be a low-fat vegan diet.)

Bix said...

Sara's comment reminded me...

Back when I was an undergrad the professor asked, "What are the top 3 risk factors for a heart attack?"

He was looking for:

- Being male
- Smoking
- I think the other one was advancing age.

Of course, there are others. But I never fully signed on to the 'being male' one. Women may experience heart attack later, but their risk is as high as men's after menopause. Heart disease is the top killer of women, and about as many women as men die of it. So, to this day I still think putting gender on that risk list is ... risky.

Laurie Endicott Thomas said...

My cholesterol went from about 170 to 120 after I eliminated dairy foods and eggs. I was already abstaining from meat and fish.

Sara, I said that the MAIN risk factor for coronary artery disease is total cholesterol. Once you keep your total cholesterol below 150 mg/dL, your arteries become self-cleaning. Check this out:

Bix said...

That's a considerable drop.

I believe in a low-fat, plant-based diet. I believe it can lower cholesterol, assist with weight loss, assist management of blood glucose, among other things.

I know a number of people who say it doesn't work for them. But Esselstyne's work is very convincing.