Men with high levels of vitamin A (retinol) in their blood have a lower risk for aggressive prostate cancer, but simply eating more vitamin A-rich foods may not be enough to reduce a man’s odds of getting the disease, according to a study in the April issue of Cancer Epidemiology Biomarkers & Prevention.
Prostate cancer is one of the most common cancers in men, second only to lung cancer. One out of every six men will face a diagnosis of prostate cancer during his lifetime. In their efforts to find new ways of preventing prostate cancer and other cancers, researchers have recently begun to focus on vitamin A, a fat-soluble vitamin that helps regulate the growth and death of cancerous cells.
Several studies have investigated the connection between vitamin A levels in the blood and prostate cancer risk, but they have had mixed results. In the current study, researchers looked at this connection among a large group of male patients enrolled in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial.
The researchers compared 803 prostate cancer patients with 844 cancer-free controls. They divided the participants into five groups based on the levels of vitamin A in their blood. Men with the highest vitamin A levels had a slightly lower risk of prostate cancer overall, but their risk for aggressive prostate cancer was reduced by more than 40 percent compared to those with the lowest vitamin A levels. Other prostate cancer risk factors, such as age, smoking, and family history did not influence this finding.
Why might vitamin A levels have affected aggressive prostate cancer specifically? “It is possible that these findings reflect differences in the etiology for [cause of] nonaggressive and aggressive prostate cancers,” says lead author Jeannette Schenk, MD, RD, of the Fred Hutchinson Cancer Research Center Prevention Program in Seattle, Washington. “In addition, retinol might have a specific effect on the development of aggressive prostate cancer.”
Studies in both cell and animal models have suggested that retinol plays a significant role in the growth, development, and death of prostate cancer cells. Specifically, retinol may prevent cells from transforming into cancer, and it may trigger the death of cells that do turn cancerous.
Although this study finds that having high levels of vitamin A in the blood can reduce a man’s risk of developing aggressive prostate cancer, simply eating vitamin A-rich foods or taking supplements may not be enough to affect the risk. Retinol concentrations have more to do more with the body’s natural processes and are affected by factors such as body mass index, physical activity, and the amount of fat in the diet. Diet and supplements alone won’t do much to increase vitamin A levels in the blood, says Dr. Schenk.
Before any recommendations can be made about vitamin A and prostate cancer risk, “More research is needed to better understand the internal factors that regulate vitamin A metabolism and serum retinol levels,” she says. Additional research is also needed to determine whether the same factors that affect vitamin A metabolism and blood retinol levels in the body also affect prostate cancer risk.
Schenk JM, Riboli E, Chatterjee N, Leitzmann MF, Ahn J, Aibanes D, Reding DJ, Wang Y, Friesen MD, Hayes RB, Peters U. Serum retinol and prostate cancer risk: a nested case-control study in the prostate, lung, colorectal, and ovarian cancer screening trial. Cancer Epidemiol Biomarkers Prev. 2009;18:1227-1231.
American Cancer Society. What are the key statistics about prostate cancer?