Lycopene, the red pigment that colors tomatoes. Source: Jeff Dahl, Wikimedia Commons
Finding ways to facilitate the prevention of prostate cancer remains an important area of research, as prostate cancer is still the second leading cause of cancer deaths among men in the United States.
In a new prospective study on the role of dietary lycopene in reducing the risk of prostate cancer, Edward Giovannucci, MD, of the department of nutrition at the Harvard School of Public Health, and colleagues found that consuming foods high in lycopene is linked to reduced risk of lethal prostate cancer. They suggest that with the advent of prostate-specific antigen screening, which has resulted in an uptick of asymptomatic, early-stage, and indolent prostate cancer diagnoses, the more relevant endpoint for lycopene studies may be the detection of lethal prostate cancer rather than indolent disease. The study was published in the Journal of the National Cancer Institute.
Higher intake of dietary lycopene was inversely associated with any prostate cancer, with the strongest association for lethal prostate cancer (hazard ratio of 0.47; P = .009). Higher lycopene consumption was also associated with prostate tumors with less angiogenic potential, according to the study authors.
Lycopene-a carotenoid and antioxidant found in red colored fruits and vegetables-has been investigated in many studies for its potential ability to prevent the development of prostate cancer. Earlier studies provided evidence that consumption of foods high in lycopene, such as tomatoes and tomato-rich products like tomato paste, can reduce prostate cancer risk by as much as 25% when high levels of lycopene in the blood serum were detected. But more recently, studies have found either no association or an inverse association. For example, a 3,500-participant study conducted at the Fred Hutchinson Cancer Research Center in 2011-one of the largest studies to examine the role of lycopene in protection against prostate cancer-found no association when participants’ blood samples were analyzed for lycopene levels.
The new study analyzed dietary data from 49,898 men participating in the Health Professionals Follow-Up Study. Men between the ages of 40 and 75 were enrolled and submitted questionnaires every 2 years on lifestyle and health, and every 4 years on dietary habits. The new study re-evaluated the dietary questionnaire data from 1986 through 2010. A previous assessment of the data from this same cohort showed that dietary lycopene was linked to a 20% lower risk of prostate cancer.
In the current analysis, baseline height, body mass index, history of prostate cancer, smoking history, total dietary calorie intake, total carbohydrate consumption, and percentage of PSA screening did not vary in the different quintiles of lycopene consumption. Men in the upper quintiles of lycopene consumption tended to be slightly younger (median 52.9 years of age vs 56.8 years of age for the lowest quintile) and more likely to do vigorous physical activity. The men who ate more lycopene consumed higher amounts of tomatoes and tomato products, such as tomato juice and pizza. The men who consumed more lycopene also tended to consume less alcohol, coffee, and all types of fat, but more fruits, vegetables, and fiber.
Compared with the bottom quintile of lycopene consumption, the top quintile was associated with a hazard ratio of 0.72 for total prostate cancer and a hazard ratio of 0.47 for lethal prostate cancer. The difference in median lycopene levels between the highest and the lowest quintiles was fourfold (3,160 mg/day compared with 13,391 mg/day).
In a subanalysis of only men who had undergone PSA screening and had at least one negative test result, the highest lycopene intake quintile was inversely associated with lethal prostate cancer (P = .009). “Men with the highest intake were half as likely to develop lethal prostate cancer compared with those with the lowest intake,” stated the authors. Consumption of lycopene earlier in the study was more strongly associated with lower risk compared with more recent lycopene consumption, which the authors suggest supports the idea that long-term or early dietary lycopene intake may be more relevant for prostate cancer prevention, particularly prevention of aggressive prostate tumors.
Using archival fixed tumor samples from 1,180 men who were diagnosed with clinical localized prostate cancer through 2002 and underwent prostatectomy or transurethral resection of the prostate, the study authors found that men who consumed higher levels of lycopene had tumors with less angiogenic potential. The blood vessels of these tumors had smaller diameters, consisted of a smaller area, and were less irregular compared with those from men in the lower quintiles of lycopene consumption.
Studies linking dietary intake with clinical outcomes are generally difficult to conduct. In the case of lycopene, the antioxidant can be difficult to measure in foods and its bioavailability can vary greatly. The strengths of the current study included the number of participants, repeated measurements of lycopene consumption, the ability to track changes in diet over a longer time frame, and the ability to assess tumor samples. Limitations included the inability to account for all possible confounding factors and the use of participant-reported data.