Prostate Cancer is a type of cancer that develops in the prostate gland of the male reproductive system (ACS, 2010) .  The occurrence of prostate cancer varies widely across the world, suggesting that a major role is played by lifestyles and dietary factors. Areas such as Europe and the United States experience more frequent cases, while other areas such as South and East Asia have less frequent cases. Prostate cancer commonly occurs in men over 50 years (ACS, 2010) . Scientists have not been able to have a complete understanding of the causes of prostate cancer. However the primary risk factors have been established to be age, family history and obesity (ACS, 2010) .

A study was conducted by Brasky et al. to investigate the role of serum phospholipid fatty acids and prostate cancer risk ( 2011) . The study was based on the knowledge that inflammation may play a major role in the development and progression of cancer. The study therefore, examined the association between inflammation that is related to phospholipid fatty acids and the prevalence of prostate cancer in a nested case-control analysis of participants (Brasky, Till, White, & Neuhouser, 2011) . The findings of the study established no association between low-grade prostate cancer risk and fatty acids. However, docosahexaenoic acid was found to be positvely associated with high grade disease (Brasky, Till, White, & Neuhouser, 2011) . These findings suggested a complex relationship between fatty acids and prostate cancer risk (Brasky, Till, White, & Neuhouser, 2011) .

Recent studies have indicated that there might be an association between fish oil and the development of prostate cancer. Fish oil oils are made up of the omega-3 fatty acids; eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (Swansom, Block, & Mouse, 2012) . A number of studies have associated EPA and DHA to various health benefits, including anti-cancer effects. Various studies have reported conflicting accounts on whether fish oil has positive effect, negative effect or no effect on the development of prostate cancer (Swansom, Block, & Mouse, 2012) .  Laboratory investigations have indicated that n-3 fatty acids inhibit and n-6 fatty acids stimulate prostate tumor growth, but it still remains unclear if the dietary intake of these fatty acids affects the risk of prostate cancer in human beings (Leitzmann, et al., 2004) However, not all epidemiologic  studies support these findings (Chavarro, Stampfer, Li, Campos, Kurth, & Ma, 2007) .

A comprehensive assessment of the association between fish consumption and prostate cancer was conducted by Szmanski et al (2010) . The study analyzed the association of fish intake and prostate cancer by focusing on the incidence of the prostate cancer and prostate-cancer-specific mortality, and included a subgroup analyses that was based on race, fish type, method of fish preparation, and occurrence of high-grade and high-stage cancer (Szmanski, Wheeler, & Mucci, 2010) . The analysis did not establish any association between fish consumption and any subsequent significant reduction in the incidence of prostate cancer (Szymanski, Wheeler, & Mucci, 2010) .  The researchers were unable to perform a meta-analysis for the high grade prostate cancer disease.  The study however established an association between fish consumption and significant (63%) reduction in prostate cancer-specific mortality (Szymanski, Wheeler, & Mucci, 2010) . It was concluded that that, even though there was no strong evidence to show a protective association between fish consumption and prostate cancer incidence, fish consumption was linked to a significant reduction in prostate cancer-specific mortality (Szymanski, Wheeler, & Mucci, 2010) .

A study conducted by Leitzmann et al. prospectively evaluated the association between the intake of alpha-linolenic (ALA; 18:3n-3), eicosapentaenoic (EPA; 20:5n-3), docosahexaenoic (DHA; 22; 6n-3), linoleic (LA; 18:2n-6), and arachidonic (AA; 20:4n-6) acids and the risk of developing prostate cancer (2004) . The researchers studied 2965 total cases of prostate cancer in the follow-up, and up to 448 of these were identified to be advanced cases of prostate cancer (Leitzmann, et al., 2004) . The intake of ALA was not found to be associated with the risk of prostate cancer. In contrast, however, multivariate relative risks of 2.02 (95% CI: 1.35, 3.03) and 1.53 (0.88, 2.66, p=ns) were established when extreme quintiles of ALA from non-animal sources and ALA from meat and dairy sources, respectively (Leitzmann, et al., 2004) . The study did not find any association between the intake of linoleic and arachidonic acid, and the risk of prostate cancer (Leitzmann, et al., 2004) .  The researchers concluded that an increased dietary intake of ALA may result into an increased risk of the advanced form of prostate cancer. However, the intake of EPA and DHA may result in a reduced risk of total and advanced prostate cancer (Leitzmann, et al., 2004) .

A prospective study was conducted by Chavarro et al. to examine the association between polyunsaturated fatty acid levels in blood and the risk of prostate cancer (2007) .  Blood samples drawn from 14,916 healthy men were used as control during the study. The blood fatty acid level was then evaluated in 476 men diagnosed with prostate cancer during a 13-year follow-up period, and matched with the controls (Chavarro, Stampfer, Li, Campos, Kurth, & Ma, 2007) . An analysis conducted using conditional logistic regression showed that the whole blood levels of all long-chain n-3 fatty acids and of linoleic acid were inversely related to the overall risk of prostate cancer (Chavarro, Stampfer, Li, Campos, Kurth, & Ma, 2007) . The blood levels of gamma-linolenic and dihomo-gamma-linolenic acids and fatty acids, which are associated with linoleic acid metabolism, were directly associated with an increased risk of prostate cancer (Chavarro, Stampfer, Li, Campos, Kurth, & Ma, 2007) .  The study concluded that the higher blood levels of long-chain n-3 fatty acids, mostly found in marine foods, and linoleic acid, mainly sourced from non-hydrogenated vegetable oils, are linked to a reduced risk of cancer (Chavarro, Stampfer, Li, Campos, Kurth, & Ma, 2007) .

A multi-ethnic case control study was conducted to establish the risk of prostate cancer in association with circulating fatty acids (Park, et al., 2009) . The study aimed at investigating the conflicting findings on the contribution of dietary fat, including specific fatty acids, in the pathogenesis of prostate cancer.  The researchers examined the association between the erythrocyte membrane fatty acid composition and prostate cancer risk in a nested case-control study in multiethnic cohort that included African Americans, Native Hawaiians, Japanese Americans, Latinos, and Whites (Park, et al., 2009) .  The study utilized conditional logistic regression to estimate the odd ratios and 95% confidence intervals with adjustments in the case for multiple covariates (Park, et al., 2009) .

The findings of the study showed that there was no significant association between saturated, mono- and polyunsaturated fatty acids, or for the specific n-3 and n-6 fatty acids, even when the analysis was only conducted in the advanced or high grade prostate cancer (Park, et al., 2009) .  The ethnic-specific analysis showed that there was a positive association with palmitic acid (supplied primarily by palm oils, but is also found in high-saturated animal fat foods such as meat, cheese, butter, and dairy products) in Japanese Americans that was found to be significantly different from the null findings from other groups.  The study also identified an increased risk with n-3 fatty acids and the ratio of n-3/n-6 fatty acids in white people (Park, et al., 2009) .

Several other studies have shown that it is healthy to consume fatty fish, particularly for the purpose of reducing cancer risk. A study was conducted by Terry et al. to establish the relationship between fatty fish consumption and prostate cancer risk in Swedish men (2001) . The association was studied in a prospective cohort consisting of 6,272 Swedish men. In the course of the 30-year follow-up, the study established that men who did not consume any fish at all had two to three times higher occurrence of prostate cancer as compared to those who ate higher or moderate amounts (Terry, Lichtenstein, Feychting, Ahlbom, & Wolk, 2001) .  The results of the study suggested that fish consumption could decrease the risk of prostate cancer.  Similar associations have also been established in studies that investigated the relationship between fish oil and other types of cancers.

A study done by Zheng et al. investigated on the relationship between the intake of marine n-3 polyunsaturated fatty acids and the risk of breast cancer (Zheng, Hu, Zhao, Yang, & Li, 2013) . The study was carried out as a meta-analysis and systematic review of prospective cohort studies.  In these studies, relative risk and 95% confidence intervals for the occurrence of breast cancer according to fish intake and n-3 PUFA intake were evaluated (Zheng, Hu, Zhao, Yang, & Li, 2013) .  The findings of the study indicated that marine n-3 PUFA was associated with a 14% reduction in the risk of breast cancer (Zheng, Hu, Zhao, Yang, & Li, 2013) .  The researchers concluded that higher consumption of dietary marine n-3 PUFA was associated with a reduced risk of breast cancer.

However, the widely acknowledged positive role that of fish oils and fatty fish consumption in the reduction of prostate cancer risk was thrown into question by the findings of a recent study. The study was led by Theodore Brasky, and its findings were published in the Journal of the National Cancer institute ( 2013) .  The study investigated the blood levels of omega-3 fatty acids in patients who were enrolled at the Selenium and Vitamin E cancer Prevention Trial (SELECT) and evaluated more than 35,000 males aged 50 years and above in the United States, Puerto Rico, and Canada (Brasky, et al., 2013) . During the study, 834 men from the trial diagnosed with prostate cancer were compared a group of 1,393 participants who were randomly drawn from the 35,000 participants (Simon, 2013) .  The findings of the study showed that men with the highest levels of omega-3 had a paradoxical 43 percent higher risk of developing prostate cancer, and a 71% chance of developing a high-grade prostate cancer (Simon, 2013) .  The study did not however collect diet information on the men included in the study and, therefore, it’s not clear whether the omega-3 fatty acids in their blood were as a result of dietary supplements or food consumption (Brasky, et al., 2013) .
The results of the study have been rejected by many researchers, and practitioners who see these findings as both scientifically weak and irresponsible. This is primarily due to the large volume of scientific evidence to the contrary that indicate the health benefits of marine omega-3 fatty acids.

The suggested weaknesses of this analysis include: the failure of the study to examine the exact relationship between the intake of omega-3 fatty acids and prostate cancer; the basing of the conclusions of this study on a minimal 0.2% difference in the levels of omega-3;  the lack of epidemiological data to support the findings of the study, given the widespread consumption of fish across the world, the epidemiologic findings of lower prostate cancer risks in populations consuming high levels of fatty fish in their diets; the use of plasma measurements that did not reflect long term consumption of omega 3s, and which could be influenced by a single meal; the failure to report on the serum levels of EPA, DHA, DPAn-3; the lack of documentation to show rate of fish consumption in the study group; the study was not designed to specifically evaluate omega -3s intake, and was confounded with selenium and vitamin E, which are used in treatment regimens and could contribute beneficial or deleterious effects; the CPH model used did not show a statistically significant relationship between EPA, DPA and DHA; the lead author in the study did not find similar findings in a study conducted in 2011; the test cohort included a sample of both sick and healthy individuals, and it is possible that the sickest participants in this study were taking higher levels fish oil supplements, creating a selection bias. (Advances in EPA & DHA Research, 2013) .

Summary
Numerous studies have reported on the health benefits of fish oils. Omega -3s, EPA, and DHA have widely been reported to reduce the risk of various health conditions and this is supported by findings of studies conducted over several decades. This long-standing knowledge has been challenged by the results of a recent study; Omega-3s and Prostate Cancer Risk. There are however a number or questions that about the study that challenges the credibility of the findings, and it is best to discuss these results with your personal physician before discontinuing a prescribed supplement regimen, or undertaking any new supplemental regimen.

For more information, see also: Diet, the Immune System and Prostate Cancer,
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Author's Bio: 

Dr. Steven Petrosino received his Baccalaureate (BA) degree in both Science and English from Penn State University in 1975, pursued his Masters degree (American Studies) with honors at Penn State in 1977-1978, and graduated Summa Cum Laude with a Doctorate in Nutrition from Lasalle University in 1995. He currently is enrolled in a Ph.D. program at Walden University (Public Health). In 1996-1998 he was involved in external post-doctoral research at the Ohio State University in the Department of Cancer Prevention and Natural Products Research. In 2002, he was enrolled in a post-doctoral external course (Immunobiology) at the University of Pennsylvania.

Dr. Petrosino is currently employed as a Senior Medical Science Liaison with Human Genome Sciences, Inc. He is married to the former Lynn Tutoli, and he and his wife reside in Dublin, OH. They have two children, Angela Petrosino Johnson, (32) and Aaron (28). Visit his website here: http://www.nutritionadvisor.com