High calcium absorption linked with greater prostate cancer risk

Key Points

Orlando, FL-Prostate cancer risk declines significantly in men who have a favorably low calcium-absorption genotype and low calcium intake, data from a large, population-based case-control study show.

The risk-reducing effect of the genotype and low calcium intake extended to men of all races. Men with the highest calcium consumption had a twofold greater risk of advanced prostate cancer than did men with the lowest consumption. The association with calcium intake did not hold up for localized prostate cancer, say researchers from the University of Southern California, Los Angeles.

"The association between high calcium intake and an increased risk of prostate cancer was first demonstrated several years ago in the Physicians Health Study," said co-author Glovioell W. Rowland, PhD, a postdoctoral fellow in environmental genomics at the University of Southern California, working with Sue A. Ingles, PhD. "We have now extended that observation to a multiethnic population.

The World Cancer Research Fund has classified calcium as a probable cause of prostate cancer. Dr. Rowland and colleagues recently reported at a separate AACR meeting that the relationship between dietary calcium and prostate cancer among African-Americans is modified by the Cdx-2 polymorphism of the vitamin D receptor. The high-absorption A allele is more common among African-American men than Caucasian men, who have a lower prostate cancer risk.

Continuing the investigation into the calcium-prostate cancer link, investigators examined the relationship between dietary calcium and the risk of localized and advanced prostate cancer. The investigation involved prostate cancer patients identified from the Los Angeles County and San Francisco Bay Area components of the National Cancer Institute Surveillance, Epidemiology, and End Results Cancer Registry. Dr. Rowland and Dr. Ingles identified all cases of prostate cancer diagnosed from July 1, 1997 through Dec. 31, 2003.

The study population, known as the California Collaborative Prostate Cancer Study, comprised 1,857 men, of whom 1,140 had advanced or fatal disease and 717 had localized cancer. Hispanic and non-Hispanic Caucasians accounted for 1,357 cases of cancer and African-American men for the remaining 500 cases. Investigators also compiled an age- and race/ethnicity-matched control group of 1,096 men.

High calcium intake among Hispanic males

Analysis of calcium intake by race showed that African-American men had the lowest intake and Hispanic men the highest. For example, 29% of African-Americans had calcium intake <590 mg per day (lowest quartile) compared with 8% of Hispanics. At the opposite end of the range of calcium intake, 23% of African-Americans versus 51% of Hispanics consumed >1,182 mg per day (highest quartile). Non-Hispanic Caucasians were the most likely to take calcium supplements (54%).

A comparison of high and low calcium intake showed that men in the top quartile of calcium intake had a 70% greater risk of advanced prostate cancer compared with men in the lowest quartile (OR 1.70, 95% CI=1.32-2.18). A separate analysis of calcium intake by race showed almost a 50% increased risk of prostate cancer among all men whose daily calcium intake exceeded >680 mg (OR 1.48, 95% CI=1.25-1.77).

Vitamin D receptor calcium absorption genotype modified the effect of calcium intake on the risk of advanced, but not localized, prostate cancer. High calcium was a risk factor in all men, regardless of genotype. In those with low calcium consumption, men with the high absorption genotype were at increased risk as well.

It is important to note that African-Americans had the lowest calcium intake, yet they have the highest frequency of the high-absorption genotype. This may have health disparities significance, according to Dr. Rowland.

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A recent study found that some prostate cancer patients are not being treated according to existing guidelines for imaging. See: http://urologytimes.com/imagingpractices.