If confirmed, the finding could help identify men at risk of dying from prostate cancer long before the disease is diagnosed, researchers say.
It could also lead to a simple strategy for reducing risk in men with high-normal serum calcium.
"If we can show that men with high-normal serum calcium really are three times as likely to develop a fatal prostate cancer, we might be able to alter this risk with existing drugs that have been proven to be very safe," study researcher Gary G. Schwartz, PhD, of Wake Forest University Baptist Medical Center, tells WebMD.
Calcium and Prostate Cancer
There is good evidence that men whose diets include a lot of calcium or those who take calcium supplements are at increased risk for prostate cancer.
But since there is little relationship between dietary calcium and calcium in the blood, the new study does not address the question of how much calcium men should eat.
Doctors often measure serum calcium during routine blood tests.
"Many of your body's functions run on calcium, just like your laptop runs on electricity," Schwartz says. "Too little calcium in the blood can cause convulsions and too much can lead to a coma. Since your body cannot afford to oscillate between convulsions and coma, the range of serum calcium is tightly controlled."
Other laboratory studies suggest that calcium and parathyroid hormone -- which regulates calcium levels in the blood -- promote prostate cancer cells' growth, the study researchers report.
In their newly published study, Schwartz and colleague Halcyon G. Skinner, PhD, MPH, of the University of Wisconsin sought to test the laboratory association in humans.
They did this by examining data from a national health survey that examined participants between 1971 and 1975, known as NHANES I, and from a follow-up survey years later.
The analysis included 2,814 men who had their serum calcium levels recorded an average of 10 years before some of the men developed prostate cancer.
The follow-up survey revealed 85 cases of prostate cancer, which included 25 prostate cancer deaths.
Serum calcium levels were not found to influence prostate cancer risk overall, but men with the highest serum calcium levels were more likely to die of the disease than men with the lowest levels.
The study appears in the September issue of the journal Cancer Epidemiology Biomarkers & Prevention.
Many Questions Remain
Schwartz and colleagues are already trying to replicate their findings using data from other studies that followed men over long periods of time.
If the findings are confirmed, the researchers say parathyroid hormone or serum-calcium-lowering drugs may prove useful in prostate cancer prevention, in the same way that cholesterol-lowering drugs are used to lower heart attack and stroke risk.
But Durado Brooks, MD, MPH, of the American Cancer Society, says this is a big leap.
"It is important to keep in mind that there were only 25 cases of fatal prostate cancer," he says. "Any attempt to assess how this relates to the entire male population at risk for this disease is very preliminary."
The director of prostate and colorectal cancer for ACS, Brooks says a greater understanding of the mechanism that might link high-normal serum calcium levels with an increased risk for fatal prostate cancer would be needed before preventive treatments could be considered.
"We would need to understand the role of the parathyroid hormone and vitamin D," he says. "There are many, many unanswered questions."