by Aimee Keenan-Greene

New information for women with osteoporosis, the most common type of bone disease.

Osteoporosis occurs when the body fails to form enough new bone, or when too much old bone is reabsorbed by the body. Calcium and phosphate are minerals essential for bone formation.

Now in a new study in the journal BMJ  says calcium supplements, with or without vitamin D, can  increase the risk of cardiovascular events like heart attacks, known as myocardial infarction.

Its estimated 1out of 5 women over the age 50 have osteoporosis, and many take calcium supplements.

About half of all women over the age of 50 will have a fracture of the hip, wrist, or vertebra. 

Researchers reanalyzed the Women’s Health Initiative Calcium/Vitamin D Supplementation Study (WHI CaD Study), using the WHI dataset, and incorporated it in a in meta-analysis with eight other studies to update their recent meta-analysis of calcium supplements and cardiovascular risk.

The team lead by Mark J Bolland, senior research fellow, and  Ian R Reid, professor of medicine and endocrinology, say the WHI CaD Study is a seven year, randomised, placebo controlled trial of calcium and vitamin D (1g calcium and 400 IU vitamin D daily) in 36,282 postmenopausal women.The team looked again for incidence of four cardiovascular events and their combinations - myocardial infarction, coronary revascularisation, death from coronary heart disease, and stroke.The initial study of 36,000 women showed no increased risk for heart disease among those who received 1,000 milligrams of calcium and 400 international units (IU) of vitamin D per day, compared with those who received a placebo. However, the scientists say in that study there was a possible interaction between personaluse of calcium supplements and allocated calcium and vitamin D for cardiovascular events - meaning women in the study were also taking personal calcium supplements and could have skewed or masked the initial findings.Taking this into account and looking again, of the 16,718 women - that's 46 percent -  who werenot taking personal calcium supplements at randomization, the hazard ratios for cardiovascular events with calcium and vitamin D ranged from 1.13 to 1.22 (P=0.05 for clinical myocardial infarction or stroke, P=0.04 for clinical myocardial infarction or revascularisation).In the women taking personal calcium supplements cardiovascular risk did not alter with allocation to calcium and vitamin D. The new findings include: In meta-analyses of three placebo controlled trials, calcium and vitamin D increased the risk of myocardial infarction (relative risk 1.21 (95 percent confidence interval 1.01 to 1.44), P=0.04), stroke (1.20 (1.00 to 1.43), P=0.05), and the composite of myocardial infarction or stroke (1.16 (1.02 to 1.32), P=0.02). In meta-analyses of placebo controlled trials of calcium or calcium and vitamin D, complete trial-level data were available for 28,072 participants from eight trials of calcium supplements and the WHI CaD participants not taking personal calcium supplements. In total 1,384 individuals had an incident myocardial infarction or stroke. Calcium or calcium and vitamin D increased the risk of myocardial infarction (relative risk 1.24 (1.07 to 1.45), P=0.004) and the composite of myocardial infarction or stroke (1.15 (1.03 to 1.27), P=0.009). In an editorial commentary on this study, also appearing in the journal BMJ  Professor Bo Abrahamsen, Department of Medicine F, Gentofte Hospital, Copenhagen DK-2900, Denmark, and  Opinder Sahota, Professor of Orthogeriatric medicine, Department of Elderly Medicine, Queen’s Medical Centre, Nottingham University Hospitals, Nottingham, UK, say there is insufficient evidence to support or refute the association.They add:  This new analysis is particularly relevant because it includes calcium supplements given with vitamin D. The meta-analysis extends one previously undertaken by the same group in which calcium supplementation was associated with a significantly increased risk of stroke and myocardial infarction. It was criticized for reporting individual outcomes when the global end point was not significant, for counting events rather than people with events, and for building on studies that were not designed for cardiovascular outcomes and adjudicated accordingly. In the current study Bolland and colleagues explore the possibility that findings in the WHI study may have been masked by the widespread use of personal calcium supplements. The decision to focus on the WHI participants who did not use calcium supplements is reasonable given that the effects would be difficult to discern if both study arms had access to what was intended to be a randomised intervention. Unfortunately, although it is straightforward to remove those who were taking their own supplements from the cohort when they make up uneven parts of the randomised arms, interpreting the results is difficult because of the loss of equal randomisation. Consumer Reports  asks, since the figures now show taking calcium supplements with or without vitamin D raises the risk of heart attacks and strokes, does the risk outweigh the benefit of stronger bones?

In their health summary of the recent study they conclude:

If 1,000 people take calcium supplements (with or without vitamin D) for five years, six will have a heart attack or stroke as a result of treatment, but only three people will avoid having a fracture. So for many people, the answer is likely to be no. However, it’s important to keep in mind that the increased risk is not large. If your personal risk of having a fracture is bigger than your risk of having heart problems, calcium still may be a suitable treatment. But you may want to up the calcium in your diet first. That’s because, while calcium supplements seem to raise heart attack risk, eating a diet rich in calcium does not. The researchers say this may be because supplements quickly raise the level of calcium in the blood stream. Calcium in food is likely to be absorbed more slowly.
The Institute of Medicine (IOM) recommendations for calcium and vitamin D intake are 600 international units (IU) of vitamin D every day for most healthy adults under age 71 and 800 IU for healthy people age 71 and older.

This recent increase ups the previous IOM recommendations of 200 to 400 IU per day for healthy adults under age 71, and 600 IU per day for those age 71 and older.  

However, the National  Osteoporosis Foundation (NOF) recommends more: healthy people age 19 to 49 need to get 400 to 800 IU of vitamin D every day; and adults age 50 and older need 800 to 1,000 IU every day. 

The NOF says 10 million Americans have osteoporosis, 34 million more have low bone mass.  In women, 85 percent of lifelong adult bone mass is acquired by age 18.  The medical cost of treating osteoporosis related bone fractures by the year 2025 in the US is estimated to be 25 billion dollars.