The amount of calcium and vitamin D in the diet appears to have little or no impact on the risk of prostate cancer, but the consumption of low-fat or nonfat milk may increase the risk of the malignancy, according to the results of two studies published in the American Journal of Epidemiology.
Dietary calcium and dairy products have been thought to increase the risk of prostate cancer by affecting vitamin D metabolism. Data from several prospective studies have supported an association, but many other studies have failed to establish a link.
To explore this topic further, Dr. Song-Yi Park, from the University of Hawaii in Honolulu, and colleagues, analyzed data from subjects enrolled in the Multiethnic Cohort Study. This study, conducted between 1993 and 2002, included adults between 45 and 75 years old, were primarily from five different ethnic or racial groups, and lived in California or Hawaii.
A total of 82,483 men from the study completed a quantitative food frequency questionnaire and various factors, such as weight, smoking status, and education levels were also noted, Park's group said.
During an average follow-up period of 8 years, 4,404 men developed prostate cancer. There was no evidence that calcium or vitamin D from any source increased the risk of prostate cancer. This held true across all racial and ethnic groups.
In an overall analysis of food groups, the consumption of dairy products and milk were not associated with prostate cancer risk, the authors found. Further analysis, however, suggested that low-fat or nonfat milk did increase the risk of localized tumors or non-aggressive tumors, while whole milk decreased this risk.
In a similar analysis, Dr. Yikyung Park, from the National Cancer Institute at National Institutes (NIH) of Health in Bethesda, Maryland, and colleagues investigated the relationship of calcium and vitamin D and prostate cancer in 293,888 men enrolled in the NIH-American Association of Retired Persons Diet and Health Study, conducted between 1995 and 2001. The average follow-up period was 6 years.
It has long been thought that dairy products can interfere with the cancer-fighting properties of vitamin D, but the consumption of low-fat or nonfat milks appears to increase the risk that the tumors become malignant.
No link between total or supplemental dietary calcium and the total number of non-advanced prostate cancer cases was noted. Total calcium intake was tied to advanced and fatal disease, but both associations fell short of statistical significance.
Similar to the first study's findings, skim milk was linked with advanced prostate cancer. Calcium from non-dairy food, by contrast, was tied to a reduced risk of non-advanced prostate cancer.
"Our findings do not provide strong support for the hypothesis that calcium and dairy foods increase the risk of prostate cancer. The results from other large...studies, with adequate numbers of advanced and fatal prostate cancers, may shed further light on this question," Park's team concludes.
SOURCE: American Journal of Epidemiology, December 1, 2008.
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