Last week, a study blanketed the internet with headlines like “Calcium Supplements Linked to Heart Attacks” (LA Times). The funny thing is, the findings really aren’t new, and they are still somewhat inconclusive.
Dr. Ian Reid of the University of Auckland in New Zealand and his colleagues combined results from 11 randomized controlled trials of calcium supplements. In other words, this was a composite analysis of prior studies that involved a total of roughly 12,000 patients – post-menopausal women specifically.
The most recent study they analyzed was done in January, 2008, and it was also led by Dr. Reid. In that study they followed 1,471 healthy postmenopausal women, ages 55 and above, assigning half to get a daily calcium supplement of 1,000 milligrams and half to placebo pills. The average age in both groups was 74.
They were particularly interested in this age group since calcium supplements are frequently prescribed to post-menopausal women in an effort to preserve bone health. Prior studies also suggested that calcium supplementation could in effect protect heart health by improving the good cholesterol: bad cholesterol ratio.
The women in the supplement group got 861 milligrams of calcium from diet per day, on average, boosting their total daily intake to 1,861. The placebo group averaged about 853 milligrams of calcium daily from their diet. So they were roughly on par for dietary intake.
However, over the course of the five year study, the group that supplemented with calcium suffered 36 heart attacks among 31 women, while the group without supplementation suffered only 22 heart attacks among 21 of the women. These results show a 1.5 times great heart attack risk in the supplement group. It seems though, that this level is still not considered “statistically significant.”
In July 2010, when Reid and his team of researchers combined this study with prior studies, they found an over 30% greater risk of heart attack among those who supplemented with calcium.
So how could calcium supplements alone possibly affect heart attack risk? As reported in Reuters:
"When you take calcium supplements, your blood calcium level goes up over the following four to six hours and goes up to the top end of the normal range," he said.
"That doesn't happen when you have calcium to eat in your diet because the calcium from food is very slowly absorbed and so the blood calcium level hardly changes at all."
Higher blood calcium may lead to the formation of plaques in blood vessels, which can lead to heart attack, stroke and other cardiovascular diseases, Reid explained.
Unfortunately, the studies did not examine the effects of calcium taken with vitamin D, the form doctors frequently recommend. Many argue that this could drastically affect the results. Also, other factors must still be taken into account, larger studies will need to be done, and statistical significance must be reached. And for dairy-free consumers, is more calcium really needed beyond diet? The hypothesis that once linked osteoporosis to low calcium intake has been debunked in many studies, which leaves us wondering, do we really have a need more calcium or could it actually do more harm? And what about calcium-fortified foods? Does the absorption rate of these delivery methods behave more like natural "calcium from diet" or supplements?
Also, Dr. Reid states that it is an issue with calcium supplements specifically. Yet in his primary study, the two groups of women are consuming equivalent levels of calcium through diet, but half are then given 1000mg of supplementation for a whopping 1850mg of calcium per day total. Have any five year studies for post-menopausal women actually been done where they were consuming 1850mg of calcium per day through diet alone? That would be roughly 6 8-ounce glasses of milk every day for dairy-drinking females. No easy feat. Without having looked at dietary calcium at that level also, it would be difficult to make the assumption that it is the supplements themselves rather than a total calcium intake that is simply too high.
I have a feeling though that Dr. Reid will not stop with the research until he reaches a more conclusive result on the calcium-heart attack connection, so I will look forward to seeing what he finds in the future.
- WebMD, 2008: Calcium May Increase Heart Attack Risk
- Reuters, 2010: Calcium supplements may raise risk of heart attack
Article by Alisa Fleming, founder of GoDairyFree.org and author of Go Dairy Free: The Guide and Cookbook for Milk Allergies, Lactose Intolerance, and Casein-Free Living.