Since I’ve been utilizing coronary calcium CT scans to detect early atherosclerotic plaque (see here) in my patients, I have frequently been asked about the relationship between calcium supplements and heart attack risk.
For example, Mrs. Jones has just found out that she has a very high calcium score and that it reflects the amount of atherosclerotic plaque lining and potentially clogging the coronary arteries to her heart. She has also been taking calcium and Vitamin D supplements recommended to her to prevent bone thinning and fractures in the future.
Did all that extra calcium she was consuming end up depositing in her coronary arteries, thus increasing her risk of heart disease?
This is a complex and not fully settled issue, however, there is enough evidence to suggest that we be cautious about calcium supplements.
A recent meta-analysis (Bolland MJ, Avenell A, Baron JA, Grey A, MacLennan GS, Gamble GD, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ 2010;341:c3691) of cardiovascular events in randomized, placebo controlled trials of calcium supplements (without vitamin D co-administration) showed that calcium supplements significantly increased the risk of myocardial infarction by 31% in five trials involving 8151 participants.
A recent meta-analysis of trials involving calcium and Vitamin D supplements found a similar increased risk of cardiovascular disease in the subjects randomized to taking calcium and Vitamin D.
These authors concluded
“in our analysis, treating 1000 patients with calcium or calcium and vitamin D for five years would cause an additional six myocardial infarctions or strokes (number needed to harm of 178) and prevent only three fractures (number needed to treat of 302”
How Might Calcium Supplements Increase Cardiovascular Risks?
Calcium supplements acutely and chronically increase serum calcium concentration. Higher calcium levels are associated with more carotid artery plaque, aortic calcification, and a higher incidence of heart attack and death.
Just like atherosclerosis, the process of calcium deposition into the arteries is very complex. Higher calcium levels could alter certain regulators of the process, such as fetuin A, pyrophosphate and bone morphogenic protein-7 or bind to calcium receptors on vascular smooth muscle cells lining the arteries
Higher calcium levels may also promote clot formation.
Bone Fracture versus Heart Attack
The informed doctor would have to tell Mrs. Jones that her calcium supplements may have contributed to her advanced coronary calcium and raised her risk of heart attack and stroke.
As with all medications, she and her doctor are going to have to discuss the relative risks and benefits.
If she has great concerns about fractures and has very low bone mineral bone density (osteoporosis) along with no family history of premature heart disease then the calcium supplementation may be appropriate.
Conversely, if she has high risk factors for coronary heart disease and/or a strong family history of premature coronary heart disease and only slightly low bone mineral density, avoiding the calcium supplements would be appropriate.
Preventing Fractures and Heart Attacks
It’s best to get calcium from the foods we eat rather than a sudden concentrated load of a supplement. Full fat dairy products like yogurt and cheese are heart healthy (see here and here) and they are an excellent source of calcium.
Weight-bearing exercise (such as running/jogging/hiking) and strength-building exercise (lifting weights, resistance machines, etc.) are also important for strengthening bones.
Thus, eating full fat dairy and aerobic exercise will help prevent both a fracture and a heart attack.