Sudden Cardiac Arrest (SCA) is fatal for over 90% of patients. Between 50-70% of those experiencing SCA have no clinical history of heart disease before the event, or are recognized as being at high risk , so identifying risks of SCA are really important. Can having a low blood calcium level cause a heart attack? If you have too little calcium in your diet are you at risk for sudden cardiac arrest?
This is what a recent study asked when it compared two groups of people from a large database in the Northwest United States. The researchers looked at 267 people who experienced “Sudden Cardiac Arrest” (SCA) and compared them to 445 cases randomly selected as controls. All the patients were over 18 years old and about 66-71% were men. To correct for potentially false blood calcium readings every patient who was enrolled in the study had to have had kidney function, albumin and calcium levels tested within 90 days of the SCA. What did they find?
Surprisingly the patients with a blood calcium levels below 8.95 mg/dL (normal = 8.5 – 10.2 mg/dL) had a 2.3x increased risk of sudden cardiac arrest compared to those with a level over 9.55mg/dL. Calcium levels in the study were corrected for albumin levels, a blood protein, to assure that the levels being compared were equivalent. Notice that 8.95 mg/dL is “Normal” but may still represent a clinical risk.
A low blood calcium level can result from any number of conditions.(see EHMD University link below) It is important to note that you cannot make a “causal connection”, based on this study, between blood calcium levels and SCA, More research is needed to better understand these findings and make that kind of linkage. The question is, would those in the lower quartile (below 8.95 mg/dL) benefit from additional calcium intake or supplementation?
The Iowa Women’s Heart Study looked at 34,486 postmenopausal women and found those with a higher oral intake of calcium had a reduced ischemic heart disease mortality after 8 years of follow-up (1). However, as is often the case, another study of 1471 women in New Zealand, in a randomized, placebo controlled study, found that heart attack was MORE common in the calcium supplement group of women than the controls after 5 years (2). Still other studies have shown no impact at all.
The challenge is that your blood calcium level is very tightly regulated hormonally and so you have little leverage in changing the levels with diet or supplements (see EHMD University link below). While taking a supplement, or increasing your calcium intake seems as though it would result in an increased level of calcium in your blood, it is not that closely linked.
My Recommendation: After discussing it with your doctor, if there are no contraindications, men and women with serum (blood) calcium levels below 8.95 mg/dL should take modest calcium supplementation (500-1000mg), as a precaution pending further research in this area. Calcium Citrate is more easily absorbed and bioavailable. Companies whose products I like include Metagenics and Orthomolecular, though there are many other fine products available. I also suggest being sure you are getting the RDA of vitamin D (600IU) each day
Mayo Clinic Proceedings October 2017 Volume 92, Issue 10, Pages 1479-1485
(1)Bostick, R.M., Kushi, L.H., Meyer, K.A., Sellers, T.A., and Folsom, A.R. Relation of calcium, vitamin D, and dietary food intake to ischemic heart disease mortality among postmenopausal women. Am J Epidemiol. 1999; 149: 151–161
(2)Bolland, M.J., Barber, P.A., Doughty, R.N. et al. Vascular events in healthy older women receiving calcium supplementation: randomized controlled trial. BMJ. 2008; 336: 262–266