Prostate cancer is the most diagnosed non-skin cancer among men within the United States, according to Centers for Disease Control and Prevention statistics. Fortunately, the incidence rate among men 50 years of age and older declined by nearly 8% per year from 2004 to 2013 (Houston, King, Li, and Jemal 2018). However, the prevalence of the late stage of this disease increased approximately 1.4% annually during the same period.
As men age, the walnut-sized prostate, located below the bladder and in front of the rectum, typically increases in size. This tissue expansion compresses the urethra, thereby decreasing urine flow. This condition, known as benign prostatic hyperplasia (BPH), does not reflect cancer. While the etiology of BPH is not well defined, many hypotheses have been advanced, such as changes or imbalance in male hormones or factors that contribute to potential chronic inflammation. Urologists often prescribe tamsulosin hydrochloride, which is an alpha-blocker that relaxes muscles in the prostate and bladder neck, thereby improving urination.
Historical recommendations for prostate health screening include measurement of prostate specific antigen (PSA), digital rectal examination, or ultrasonography (Moyer 2012). A recent assessment of the clinical value of serum PSA to detect early presentation of prostate cancer indicated the production of nearly 80% false positive results. Upon follow-up, these men often are subjected to additional testing, including at least one biopsy, and hospitalization occurs approximately 1% of the time. As a result, the U.S. Preventive Services Task Force noted that the value that PSA could contribute to the reduction of prostate cancer mortality was low and stated that the benefits of such testing did not outweigh the subsequent harm to adult males.
Approximately a decade ago, an assessment of dietary patterns among men and the potential risk of prostate cancer conducted as part of the Health Professionals Follow-up Study indicated the typical Western diet, including vegetable or fruit intake, was not associated with a risk of advanced prostate cancer, except for a modest association among men older than 65 years of age (Giovannucci, Rimm, Liu, Stampfer, and Willet 2002; Wu, Hu, Willett, and Giovannucci 2006). Another assessment of data from the Prostate Cancer Prevention Trial (1994–2003) indicated a weak association of lycopene, zinc, and vitamin D and a reduced risk of developing BPH (Kristal et al. 2008).
Plasma from a small sample of men enrolled in the 1982 Physicians’ Health Study, nearly 3% of whom developed prostate cancer during a 13-year follow-up, was analyzed for five major carotenoids, two major forms of tocopherol, and retinol (Gann et al. 1999). The findings suggested an inverse relationship between plasma lycopene and the presentation of prostate cancer. These results were similar to earlier observations that the incidence of prostate cancer decreased with increased exposure to selenium and vitamin E via supplementation (Clark et al. 1998; Heinonen et al. 1998).
Early research on lycopene metabolism involved a canine model system (Waters and Bostwick 1997). Subsequent research among male dogs on the pharmacokinetics of lycopene up to 50 mg/kg bw, indicated a broad range of lycopene accumulation in tissues, primarily in the liver and adrenal glands. This study indicated plasma lycopene approached low baseline values approximately 120 hours post administration of a single dose. Maximum plasma concentration was achieved about 12 hours post administration. An important finding is that lycopene, an all trans-configured carotenoid, is isomerized to cis-lycopene (Korytko et al. 2003). Data from a ferret model indicate the cis-isomer is more biologically available (Boileau et al.1999). These findings were reinforced among human subjects consuming tangerine tomatoes that contain about 94% cis-lycopene, whereas tomato juice contains about 10% of the cis-isomer (Copperstone et al. 2015). Additional data from another study among healthy adults indicate an endogenous trans-to-cis isomerization occurs during post-absorptive metabolic processes (Moran et al. 2015). The consistency and efficiency of this isomerization is critical for our understanding on the potential metabolism and subsequent health benefits of this carotenoid. However, a preponderance of evidence indicates thermal processing improves lycopene uptake, including the cis-isomer (Stahl and Sies 1992).
Genetic variations and androgen receptors are additional factors to consider in the diet, health, and disease continuum of prostate cancer. An increased understanding of alterations in metabolic pathways, phenotypes, and androgen receptor actions has contributed to the development of novel therapeutic pharmacological and possible dietary strategies to reduce the incidence of BPH and one of the most common global malignancies (Sissung et al. 2014; Matsumoto et al. 2013; Masko, Allott, and Freedland 2013).
Roger Clemens, DrPH, CFS, Contributing Editor
Adjunct Professor, Univ. of Southern California’s School of Pharmacy,
Los Angeles, Calif.