Ask the Doctors May 2013 Issue

Ask The Doctors: May 2013

Calcium and heart disease …Irradiated Plastic... Bone Density Testing

Q. Is it true that calcium supplement pills may actually increase my risk of cardiovascular disease? As a woman, I’ve always thought taking calcium supplements was the right thing to do to prevent bone loss, hip and spine fractures and other bone problems, but now I’m not sure what to do.

A. A recent study published in the online version of BMJ (February 13, 2013) suggests that high intakes of calcium (including diet and supplements) in women are associated with higher risk of death from all causes, particularly cardiovascular disease, compared to those with lower calcium intake. In a review of more than 60,000 Swedish women throughout almost 20 years, the researchers found that those who ingested a high-calcium diet (at least 1,400 milligrams per day) and also took calcium supplement tablets (500 milligrams daily) were more than twice as likely to die during the study as those whose diets contained between 600 and 999 milligrams of calcium daily.
Data on calcium as a risk factor for heart disease is controversial at the present time. Several studies have shown a link, especially with higher calcium intakes. Interestingly, getting your calcium in the diet as opposed to supplements did not appear to increase the risk of cardiovascular disease.

Q. I’ve read that today’s knee replaments last longer than those used in the past due to “irradiated” plastics. What is irradiated plastic, and why is it a better type of joint for my knee replacement?

A. In the past, a total knee replacement lasted about 10 years before the plastic wore out, but thanks to new technology today’s knee replacements survive at least 15 to 20 years. One factor in the increased survival of modern knee replacement is the use of highly irradiated plastic, or ultra-high molecular-weight polyethylene that is more durable than earlier versions used in knee replacement. Irradiation of the plastic causes cross-linking of its molecules, resulting in a stronger, more wear-resistant plastic that can prolong the life of a knee replacement. A knee replacement joint is typically made of a flat metal plate and stem implanted in the tibia; the plate has a cushion of polyethylene to interact with a contoured metal implant placed around the end of the femur, allowing the knee to flex and extend. The stronger, more durable irradiated plastics increase the length of time a total knee replacement will function well, making the procedure more practical for younger patients.

Q. My doctor has recommended I have a bone density test to gauge my risk of osteoporosis. How important is a bone density test, and how often should I have it completed?

A. The American College of Rheumatology (ACR) recently published guidance in the journal Arthritis Care and Research (March 2013) suggesting that DXA scans should not be completed more often than once every two years. The interval between bone density testing depends on a number of factors. Is your bone density near the level at which you would consider treatment, but not quite low enough to treat? In this case, a two-year density is reasonable. For patients on glucocorticoids (Prednisone) as well as patients with hyperparathyroidism, a follow-up bone density is recommended every year. If the bone density is normal or shows only mild osteopenia, a longer interval of two years is reasonable. If you have had two bone density tests that show stable bone mass two years apart, the next bone density can be ordered at an interval greater than two years. The actual time between bone density testing can vary from one to 10 years or more, depending on the patient.