Calcium supplements are widely promoted in popular media, and routinely prescribed by both medical doctors and naturopaths to postmenopausal women, particularly those who have been diagnosed with low bone density. Many vegans consume calcium supplements and/or calcium-fortified foods because they worry that their dietary intake of calcium may be inadequate.
Because calcium is a mineral found abundantly in our food supply, it has long been assumed that raising calcium intake, through either higher intake of dairy products or supplementation, is at worst harmless, and at best beneficial to our bones.
But an editorial published in the medical journal Heart pulls together multiple strands of evidence which strongly indicate that both those assumptions are false.
Here are some disturbing facts on calcium supplements:
#1. Calcium supplementation raises the risk of renal calculi (kidney stones) by about 20%.
The pain caused by kidney stones is so excruciating, it is often described as one of the strongest pain sensations humans can experience – and the closest men (who comprise 80% of kidney stone cases) ever get to the pain of childbirth!
Taking calcium supplements was found to raise the risk of kidney stones by 20% in the Nurses’ Health Study (1) and by 17% in the Women’s Health Initiative trial (2).
#2. Calcium supplements substantially raise your risk of heart attack.
A metanalysis of 15 randomised, placebo-controlled trials of calcium supplementation, involving over 20 000 patients aged 40+ who were followed up for a year or more, found that patients allocated to calcium supplementation had around a 30% greater risk of suffering a heart attack (3).
Patients with renal failure (who are often given calcium supplements to lower their blood phosphate level) are at even higher risk: calcium pills dramatically accelerate coronary-artery calcification, contributing to the very high cardiovascular death rate in this population (4, 5, 6).
#3. Taking calcium supplements nearly doubles your risk of admission to hospital with an acute abdominal condition.
A review of adverse events from 7 randomised clinical trials of calcium supplementation, found that taking calcium supplements caused a plethora of gastrointestinal complaints. Constipation, excessive abdominal cramping, bloating, severe diarrhoea or abdominal pain, upper gastrointestinal events and gastrointestinal disease were over 40% more likely to afflict people taking calcium pills than those taking placebo
Most worryingly, those on calcium pills were 92% more likely to require hospitalisation for an acute gastrointestinal condition (7).
#4. Elderly people have a higher risk of dying when they take calcium supplements.
A randomised, controlled trial conducted on 602 elderly, frail Australians found that those given 600 mg of calcium per day plus daily sunshine exposure, had a 47% increase in total mortality and a 76% increase in cardiovascular mortality compared to those receiving sunshine exposure alone (8).
#5. Taking calcium supplements does NOT reduce fracture risk.
This is the real kicker. The aggressive marketing activities of calcium pill manufacturers have managed to persuade almost the entire populace – including the vast majority of doctors – that raising calcium intake is the most important step we can take to lower the risk of bone fractures. Yet the authors of the Heart article point out that
“the anti-fracture effects of calcium are modest, having been demonstrated in only two studies of calcium plus vitamin D, and suggested to be of the order of about 10% reduction, in meta-analyses” (9).
And by contrast, several trials have found that higher calcium intake either has no effect on the risk of suffering a bone fracture risk, or actually increases it!
For example, an 18 year prospective analysis involving 72 337 postmenopausal women found that neither total calcium intake nor dairy product intake had any protective effect against bone fractures, while vitamin D intake was strongly protective (10).
The Women’s Health Initiative study referenced above (2) found that although
“calcium with vitamin D supplementation resulted in a small but significant improvement in hip bone density, [it] did not significantly reduce hip fracture.”
And a study of 61 433 Swedish women, who were followed up for 19 years, found that those with the highest intake of calcium had a 19% higher risk of suffering a fracture (11).
There are proven, safe and effective ways to build your bone health and decrease fracture risk, without the scary side-effects of calcium supplements! To find out more, read my article The top 5 tips for building strong, healthy bones.
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