Several large studies have linked higher blood levels of long-chain omega-3s with higher risks of prostate cancer. However, other research has shown that men who frequently eat seafood have lower prostate cancer death rates and that dietary intakes of long-chain omega-3s aren’t associated with prostate cancer risk. The reason for these apparently conflicting findings is unclear. 
Omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential nutrients that have potential preventive and therapeutic effects on psychiatric disorders, such as anxiety and depression,7-15 as well as comorbid depression and anxiety in physically ill patients,16-19 patients with coronary heart disease,20,21 and pregnant women.22,23 Preclinical data support the effectiveness of omega-3 PUFAs as treatment for anxiety disorders. Song et al24,25 found that an EPA-rich diet could reduce the development of anxiety-like behaviors in rats as well as normalize dopamine levels in the ventral striatum. In addition, Yamada et al26 showed that a high dietary omega-3 to omega-6 PUFA ratio reduced contextual fear behaviors in mice and that these effects were abolished by a cannabinoid CB1 receptor antagonist.
Other suspected health benefits of omega-3s and fish are less well established and need further study. They include suggestions of a reduced risk of breast cancer, colorectal cancer and possibly advanced prostate cancer, all related to eating fish rather than taking supplements. Some observational studies have associated omega-3s to a lower risk of cognitive decline, Alzheimer’s disease and dementia, as well as age-related macular degeneration.
Evidence linking fish oil and cancer has been all over the map. Some research suggests diets high in fatty fish or fish oil supplements might reduce the risk of certain cancers, including prostate cancer. Other research shows just the opposite, a  link between eating a lot of oily fish or taking potent fish oil supplements and a 43% increased risk for prostate cancer overall, and a 71% increased risk for aggressive prostate cancer.
Fish oil supplements vary in the amounts and ratios of DHA and EPA they contain. For example, salmon oil naturally contains more DHA than EPA; a supplement derived from algae may only contain DHA. Krill oil contains significant amounts of both EPA and DHA. Read the labels and remember whatever supplement you buy, it must have at least 600 mg of DHA.
There’s more good news when it comes to fish oil and eye health, and it’s just not just for diabetic this time. Fish oil has been shown to reverse age-related eye disorders. In March 2014, French researchers evaluated 290 patients with age-related macular degeneration (AMD), and they discovered that dietary oil fish and seafood intake were significantly lower in AMD patients. Due to the high EPA and DHA levels in fish oil, it was concluded that this kind of nutritional intervention could especially benefit those at high risk for neovascular age-related macular degeneration. (24)
CONDITIONS OF USE AND IMPORTANT INFORMATION: This information is meant to supplement, not replace advice from your doctor or healthcare provider and is not meant to cover all possible uses, precautions, interactions or adverse effects. This information may not fit your specific health circumstances. Never delay or disregard seeking professional medical advice from your doctor or other qualified health care provider because of something you have read on WebMD. You should always speak with your doctor or health care professional before you start, stop, or change any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you.
Heterogeneity was examined using the Q statistic and the corresponding P values,41 and the I2 statistic was used to evaluate the proportion of variation resulting from among-study differences. Any possible publication bias was detected with both funnel plots and Egger regression in the main part of the meta-analysis.42 By using Duval and Tweedie’s trim-and-fill test, we adjusted the effect sizes for potential publication bias if there was evidence of publication bias detected by this test in the Comprehensive Meta-analysis statistical software, version 3.43 To investigate the potential confounding effects of any outliers within the recruited studies, sensitivity testing was conducted with the 1-study removal method to detect the potential outliers.44

Meta‐analysis and sensitivity analyses suggested little or no effect of increasing LCn3 on all‐cause mortality (RR 0.98, 95% CI 0.90 to 1.03, 92,653 participants; 8189 deaths in 39 trials, high‐quality evidence), cardiovascular mortality (RR 0.95, 95% CI 0.87 to 1.03, 67,772 participants; 4544 CVD deaths in 25 RCTs), cardiovascular events (RR 0.99, 95% CI 0.94 to 1.04, 90,378 participants; 14,737 people experienced events in 38 trials, high‐quality evidence), coronary heart disease (CHD) mortality (RR 0.93, 95% CI 0.79 to 1.09, 73,491 participants; 1596 CHD deaths in 21 RCTs), stroke (RR 1.06, 95% CI 0.96 to 1.16, 89,358 participants; 1822 strokes in 28 trials) or arrhythmia (RR 0.97, 95% CI 0.90 to 1.05, 53,796 participants; 3788 people experienced arrhythmia in 28 RCTs). There was a suggestion that LCn3 reduced CHD events (RR 0.93, 95% CI 0.88 to 0.97, 84,301 participants; 5469 people experienced CHD events in 28 RCTs); however, this was not maintained in sensitivity analyses – LCn3 probably makes little or no difference to CHD event risk. All evidence was of moderate GRADE quality, except as noted.
Marine and freshwater fish oil vary in contents of arachidonic acid, EPA and DHA.[15] The various species range from lean to fatty and their oil content in the tissues has been shown to vary from 0.7% to 15.5%.[16] They also differ in their effects on organ lipids.[15] Studies have revealed that there is no relation between total fish intake or estimated omega−3 fatty acid intake from all fish, and serum omega−3 fatty acid concentrations.[17] Only fatty fish intake, particularly salmonid, and estimated EPA + DHA intake from fatty fish has been observed to be significantly associated with increase in serum EPA + DHA.[17]
There have been conflicting results reported about EPA and DHA and their use with regard to major coronary events and their use after myocardial infarction. EPA+DHA has been associated with a reduced risk of recurrent coronary artery events and sudden cardiac death after an acute myocardial infarction (RR, 0.47; 95% CI: 0.219–0.995) and a reduction in heart failure events (adjusted HR: 0.92; 99% CI: 0.849–0.999) (34–36). A study using EPA supplementation in combination with a statin, compared with statin therapy alone, found that, after 5 y, the patients in the EPA group (n = 262) who had a history of coronary artery disease had a 19% relative reduction in major coronary events (P = 0.011). However, in patients with no history of coronary artery disease (n = 104), major coronary events were reduced by 18%, but this finding was not significant (37). This Japanese population already has a high relative intake of fish compared with other nations, and, thus, these data suggest that supplementation has cardiovascular benefits in those who already have sufficient baseline EPA+DHA levels. Another study compared patients with impaired glucose metabolism (n = 4565) with normoglycemic patients (n = 14,080). Impaired glucose metabolism patients had a significantly higher coronary artery disease HR (1.71 in the non-EPA group and 1.63 in the EPA group). The primary endpoint was any major coronary event including sudden cardiac death, myocardial infarction, and other nonfatal events. Treatment of impaired glucose metabolism patients with EPA showed a significantly lower major coronary event HR of 0.78 compared with the non–EPA-treated impaired glucose metabolism patients (95% CI: 0.60–0.998; P = 0.048), which demonstrates that EPA significantly suppresses major coronary events (38). When looking at the use of EPA+DHA and cardiovascular events after myocardial infarction, of 4837 patients, a major cardiovascular event occurred in 671 patients (13.9%) (39). A post hoc analysis of the data from these diabetic patients showed that rates of fatal coronary heart disease and arrhythmia-related events were lower among patients in the EPA+DHA group than among the placebo group (HR for fatal coronary heart disease: 0.51; 95% CI: 0.27–0.97; HR for arrhythmia-related events: 0.51; 95% CI: 0.24–1.11, not statistically significant) (39). Another study found that there was no significant difference in sudden cardiac death or total mortality between an EPA+DHA supplementation group and a control group in those patients treated after myocardial infarction (40). Although these last 2 studies appear to be negative in their results, it is possible that the more aggressive treatment with medications in these more recent studies could attribute to this.
Thanks to fatdog11 for that informative post about PCB’s in fish-oil supplements. Are these same toxicity levels found in fish themselves, or possibly are these levels so high only in highly concentrated fish-oil products? Also, can fatdog11 please inform us more about algae-derived omega-3. What are the DHA and EPA levels in these capsules? What is the cost, and where can they be purchased?
According to the National Psoriasis Foundation, fish oil can aid in preventing or slowing heart disease, which is especially great for psoriasis and psoriatic arthritis sufferers who are at a higher risk of developing heart disease. (27) When it comes to using fish oil supplements for the alleviation of psoriasis symptoms, studies have been mixed with some showing improvement but others showing no effect. If you suffer from psoriasis, you may want to try a fish oil supplement, or else I highly recommend that you make sure to have fish rich in omega-3s regularly.
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In fact, dietary fat intake has been among the most widely studied dietary risk factors for breast and prostate cancers. Two studies from 2002 explain how omega-3 can protect against breast cancer. BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) are two tumor suppressor genes that, when functioning normally, help repair DNA damage, a process that also prevents tumor development.
Maximizing the benefits you get from omega-3s is highly dependent on how they are absorbed and transported throughout your body. Although these fatty acids are water soluble, they cannot be easily transported into your blood in their free form. Therefore, they need to be packaged in lipoprotein vehicles for them to be better absorbed into your bloodstream.
For example, large predatory fish like shark, swordfish, king mackerel, tilefish and albacore tuna can contain high levels of methyl mercury, a toxin that would override any health benefit, especially for the developing brains of fetuses and young children as well as for adults, Dr. Nesheim and Marion Nestle, professor emerita of nutrition, food studies and public health at New York University, noted in 2014 in an editorial in the American Journal of Clinical Nutrition. (Levels of mercury and other contaminants in fish have since declined somewhat but are not negligible.)

Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.