Calcium clue

Normal 0 false false false MicrosoftInternetExplorer4 The body tightly regulates the amount of calcium in the blood, much like a surge protector keeps a computer from being fried by too much electricity. Researchers now find that even a slight excess of blood calcium may increase a man’s risk of developing lethal prostate cancer. The report appears in the September Cancer Epidemiology, Biomarkers & Prevention.

The unsettling report might actually be good news since it could provide a marker for identifying men at unseen risk of this malignancy, says study coauthor Gary Schwartz, an epidemiologist at WakeForestUniversity in Winston-Salem, N.C.

A hormone made by the parathyroid gland in the neck regulates calcium concentrations in the blood. Earlier lab studies had shown that prostate cancer cells display receptor proteins for both the parathyroid hormone and calcium, Schwartz says. Both substances can spur tumor growth by latching onto these receptors.

Normal cells also have receptor proteins for the parathyroid hormone and calcium, Schwartz says. “But prostate cancer cells have a lot of them.”

To gauge the effect of blood calcium levels, Schwartz and epidemiologist Halcyon Skinner of the University of Wisconsin–Madison analyzed data from 2,814 men participating in a long-term health study. All the men gave a blood sample at the outset. Ten years later, 25 had died of prostate cancer.

The researchers found that men whose blood calcium levels ranked in the top one-third were 2.7 times as likely to have died from prostate cancer as those in the lowest third. The researchers accounted for differences in body weight, race and age.

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“This is a great study,” says nutritionist Xiang Gao of the Harvard School of Public Health in Boston. Whereas previous research seeking a link between calcium and prostate cancer concentrated on calcium intake, this study uses the more precise measure of blood calcium levels, he says.

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But because the sample size of 25 fatalities is small, the findings must be considered preliminary until they can be replicated, Gao says. 

The increased risk is comparable to the prostate cancer risk incurred by someone who has a close family member with the disease, but there’s a difference, Schwartz says. “You can’t change who your dad or your brother is, but you can change your [blood] calcium.”

Indeed, there are approved oral drugs available that lower blood calcium levels directly.

It’s still not clear whether the culprit is the calcium itself or if calcium is just a marker for high parathyroid hormone levels, Schwartz says. But there are drugs that reduce those, too. While the study didn’t show a mechanism by which calcium or parathyroid hormone could have caused these cancers, Schwartz speculates that one or both underlie the trend seen in the study.

Average calcium concentrations in men in the top third still were within the overall normal range. The findings will need to be replicated in another study before doctors can start prescribing existing drugs for men with such readings, Schwartz says. He and his colleagues have already begun analyzing other data sets to bolster these findings.