A new study published this week that cast aspersions on calcium supplements has re-opened the debate over the value of calcium for bone health, particularly for postmenopausal women concerned about osteoporosis.
The study brings up issues of food vs. supplement sources, over what a proper bone-health supplement should look like, over bias in scientific studies, and over the best way to attain optimal health as women age.
The study in question was a re-analysis of data from the Women’s Health Initiative, a study of 36,282 postmenopausal American women. In this particular arm, women were given either 1,000mg/day calcium carbonate and 400 IU vitamin D/day or placebo for 7 years.
Those study results, published in 2009, found 744 women died who supplemented, compared to 807 women who died in the placebo group. The researchers concluded there was a non-significant trend of reduced risk of death from stroke or cancer, with no difference in other causes of death, including coronary heart disease.
The study published this week in the British Journal of Medicine took another look at the WHI data.
Researchers found that women who were taking calcium already at the start of the study were just fine. But women who were not taking calcium supplements at the start of the study (the age range of participants was 51 to 82 years old) suffered a few more deaths.
By itself, there was nothing much to conclude. So the researchers gathered 15 other studies, involving about 29,000 additional women, and came up with a headline: 25 to 30 percent increased risk of heart attacks and 15 to 20 percent increased risk of stroke.
Before you get out of the calcium supplements business, it’s important to note that that 25-30 percent increase, according to the researchers, meant that for every 1,000 patients, taking calcium or calcium with vitamin D “would cause an additional six myocardial infarctions (heart attacks) or strokes and prevent only three fractures.”
The three additional fractures prevented were called a non-issue, while the six additional heart attacks were called significant.
Calcium is good for bones
So what’s the real story with calcium? It’s the No. 2 supplement, behind vitamin C, with about 43 percent of Americans saying they take it. Everyone knows that calcium is good for bones. From an intuitive standpoint, bones are white and so is calcium. From a metabolic perspective, bones store minerals, most notably calcium as well as phosphorus. In fact, 99 percent of the calcium in the body is found in bones, and calcium by itself makes up about three pounds of weight in an average person.
That calcium is good for bones is not in dispute, and that’s why so many postmenopausal women take calcium supplements – because they are concerned with osteoporosis, with breaking bones. If you are elderly and fall and break your hip, you are not likely to live to see your next birthday.
On the other hand, the other great fear of the postmenopausal set is heart attacks – once menopause hits, women catch right up with men in cardiovascular disease and heart attack incidence. Two forms of cardiovascular disease in particular are atherosclerosis, or hardening of the arteries, and the sudden-death heart attack. The thing that hardens arteries is calcium. And sudden-death heart attacks occur because an arterial plaque deposit breaks off and blocks off blood flow. While American doctors routinely counsel patients that cholesterol is the culprit to watch, the fact remains that plaque is comprised, by and large, by (you guessed it) calcium.
Some studies show that calcifications of arteries are associated with an increased risk of heart attacks, and of associations between calcium intake and cardiovascular calcifications and osteoporosis.
Other studies show that low calcium intake equates with higher blood pressure – not good for heart health.
So, have we all been fed a line? Is calcium, at least by itself, not the answer for postmenopausal cardio health? That is to say, is this week's study results valid?
Should women stop taking calcium?
It’s important to remember the first two rules of scientific research. One is that a single study does not a conclusion make. Two is that meta-analyses – studies that pool data from a number of studies to try to form a grand conclusion – are always liable to be biased.
“Meta-analyses like the one in BMJ are a good example of how confirmation bias can influence an author’s assumptions – you find what you are looking for,” said Robert Rountree, MD, a physician in Boulder, CO. "As was the case, not one of the trials included was designed to look for an effect of calcium supplements on cardiovascular disease or heart attacks, so that automatically raises a question about the accuracy of the data."
The same researchers in this study have tilted at the calcium/cardiovascular link before. It started with a study also published in the British Medical Journal finding that 1,000mg/day calcium led to increased trends in cardiovascular events.
"The problem here is that only one group of researchers has been involved in all three of the negative studies of calcium supplementation," noted Rountree. "At this point, no other researchers have replicated these findings. But that doesn’t stop the researchers from basically telling the press that calcium supplements are dangerous."
Indeed, in an editorial that appeared in the same issue of BMJ in which the 2010 meta-analysis appeared, Dr. John Cleland strongly challenged the conclusion drawn by the author of the first study. He asked, "Why should calcium supplements increase cardiovascular risk? Calcium supplements may improve some conventional cardiovascular risk factors including blood pressure and lipids. Accumulation of calcium in the arterial wall leading to reduced compliance would be expected to take years, but the increased risk of myocardial infarction reported by Bolland and colleagues occurred early after calcium supplementation (median follow-up of 3.6 years). An alternative possibility is that the increased risk of myocardial infarction is not a true effect."
Other unassailable calcium notes: The best determinant of whether or not you’ll suffer from osteoporosis is your bone calcium content when you’re a growing adolescent. All the calcium in the world after age 50 just won’t make up for a puberty sans milk and ice cream and grilled-cheese sandwiches. A study that began in the 1930s and published in 2009 concluded that children whose family diet in the 1930s was high in calcium were at reduced risk of death from stroke, and they lived longer overall.
If it’s too late for that, calcium from dietary sources seems to be better for you than supplemental calcium. Besides dairy foods, other excellent food sources of calcium include leafy greens, especially broccoli, spinach and kale. Beans, peas and tofu also rate, as do salmon and sardines (also good sources of omega-3s).
Formulate better bone health supplements
The reason foods are better than supplements likely has to do with the bone matrix as well as the food matrix. Bones are more than calcium deep. Bones are actually living tissues that grow and degrade and reform. Keeping calcium in bones certainly helps, but calcium is hardly the only nutrient at play here.
This is an opportunity to formulate bone-health supplements with more than merely elemental calcium carbonate.
- Magnesium has long been a staple of calcium formulations, generally at a 1:2 ratio. It interrupts calcium crystals to produce flexible rather than brittle bone.
- Phosphorus, by volume the second-most prevalent element in bones, would also be a good idea.
- Vitamin D helps bones absorb calcium.
- Vitamin K2 uniquely does double-duty in both helping keep calcium in bones while also removing calcium from arteries. It has been shown to increase bone strength in animals given a low calcium diet after only three weeks.
- Boron is another nutrient of note.
Focusing on a single nutrient is likely too reductionist in thinking. Supplement makers who develop bone-health pills would do well to formulate products that more closely approximate the calcium matrix found in foods – and in bones. And then this entire calcium conundrum will be entirely academic.