Omega-3 fatty acids — do they increase or decrease prostate cancer risk?
A recent study produced confusing results. It found that a higher blood concentration of omega-3 fatty acids was associated with increased risk of high-grade prostate cancer, and a higher concentration of trans-fats was associated with decreased risk. Since these men were not supplementing with liquid fish oil, it can be assumed that their higher blood level concentrations were the result of fish intake. Before the data was collected and analyzed, the authors hypothesized the opposite, and were unable to explain the results. So how should men proceed regarding omega-3 supplementation? We know that DHA is good for the heart and the brain, but is it really bad for the prostate? What about trans-fats ? how could more of this unhealthy fat possibly be beneficial for the prostate?
Inflammation and fatty acids in prostate cancer
Chronic inflammation is a contributor to most of the chronic diseases that befall Americans ? in fact, inflammation is thought to be a causative factor in 20% of all human cancers.1 There is plenty of evidence that inflammatory processes drive the growth of prostate tumors, and that inflammatory enzymes are highly expressed in prostate tumors.2 Since in general, omega-6 fatty acids promote inflammatory processes, and omega-3 fatty acids promote anti-inflammatory processes, cell culture and animal studies have been carried out to test whether omega-3 fatty acids might slow prostate cancer cell and tumor growth.
Treatment of human prostate cancer cells with EPA or DHA (the long chain fatty acids found in fish and supplements) has consistently decreased proliferation and/or increased programmed cell death, supporting the idea that using EPA and DHA to curb inflammation could prevent or slow prostate tumor growth. In addition, omega-3 treatment has diminished pro-inflammatory gene expression and cell signaling, as well as the invasive properties of human prostate cancer cells.3-11 In animal studies, diets enriched in omega-3s either slowed (in three studies) or had no effect (in one study) on prostate tumor growth or other markers of prostate cancer progression.4, 12-14 Clearly, there are biological mechanisms by which omega-3 fatty acids can prevent the growth of prostate cancer cells and tumors.
Other studies of fish and omega-3 consumption
In 2010, a meta-analysis of 31 studies on fish consumption and prostate cancer risk was published. When pooling the data, the authors did not find a significant effect of fish consumption on prostate cancer incidence, but the individual studies varied widely in their results. The risks of prostate cancer diagnosis calculated for high fish consumption ranged from a 61% decrease in risk to a 77% increase in risk, and several showed no significant differences in risk at all.15
In the same meta-analysis, pooling data from the 4 studies that used death from prostate cancer (rather than diagnosis of prostate cancer) as the outcome, there was a 63% decrease in risk for high fish consumption. There was a greater degree of consistency in these studies ? all showed decreases in risk, although of varying sizes.15 These results, suggesting that fish consumption decreases the risk of death from prostate cancer, completely contradict the finding in the recent study on blood omega-3 fatty acids, adding more doubt to the findings.
The most recent meta-analysis of studies of ALA intake (ALA is the short chain omega-3 fatty acid abundant in plant foods like flax, hemp, chia, and walnuts, and small amounts in leafy greens) concluded that there was a small but significant decrease in risk (5%) for men consuming more than 1.5 grams of ALA per day.16 An earlier meta-analysis (2004) found a decreased risk of fatal heart disease but increased risk of prostate cancer for high ALA intake ? however, this report also mentioned that the major sources of ALA in the U.S. are mayonnaise, salad dressings, margarine, butter, and meats ? not seeds and walnuts.17 Regardless of the findings from this recent, contradictory study, if we were to conclude anything from all the studies available on this subject it would be that fish and omega-3 fats in general do not have a major impact on this disease.
Rather than relying on subjects? reports of their dietary intake, at least 15 studies (the recent study included), have used blood concentrations of omega-3 fatty acids as a measure of omega-3 intake. Unfortunately, similar to the fish consumption studies the results have been inconsistent ? some studies reported increased risk, some decreased risk, and some no effect.
In the current study, higher percentages of DHA and EPA+DHA (but not EPA only) were not associated with low grade prostate cancer, but were associated with increased incidence of high grade prostate cancer.18 In this study, very few of the men were taking omega-3 supplements, so EPA and DHA levels primarily reflect fish intake.19 Similarly in the previous studies on blood fatty acids, sometimes the results varied based on cancer grade. For example, in a large study published in 2008, high blood ALA decreased the risk of low grade prostate cancer, but increased the risk of high grade cancer. Also, EPA increased the risk of high grade cancer but had no effect on low grade cancer.20 Low grade cancers mutate into high grade cancers, so this inconsistent finding demonstrates the levels are likely caused by the cancer rather than the cause of the cancer.
Fish consumption: the good, the bad and the ugly
Why, in all of these studies on fish and omega-3 blood levels (which reflect omega-3 intake, primarily from fish), were there so many different results? Remember that when looking at fish intake, we are not looking at omega-3 intake alone. Fish are rich in omega-3s, but they also contain a significant amount of animal protein and accumulated environmental pollutants. Animal protein raises IGF-1 levels, which are linked to prostate cancer.21, 22 Regarding pollutants in fish, the Environmental Protection Agency warns primarily of mercury, PCBs, chlordane, dioxins, and DDT. High levels of PCBs and chlordane in adipose tissue are associated with significant increases in prostate cancer risk ? between 3 and 11-fold increases.23 Occupational exposure to dioxin has also been identified as a potential risk for prostate cancer.24 So the variety of findings likely represents regional differences in the type of fish consumed and the toxicity or pollution of the available fish supply. A more accurate depiction of the effects of omega-3 fatty acids on prostate cancer risk would probably be obtained from a study on omega-3 supplementation rather than fish consumption, but these studies have not yet been conducted.
The only study on the effects of omega-3 supplementation and prostate cancer risk found no association between long-chain omega-3 supplementation and prostate cancer risk or progression.25 More studies are needed to determine whether supplementation has the same beneficial effects as treatment of cultured prostate cancer cells with EPA and DHA, or heterogeneous effects on prostate cancer risk, like fish consumption.
Trans-fats and blood levels; more confusion in the midst.
Since trans fats are consumed as an ingredient in processed foods and fried fast foods, this study also demonstrated a protective effect from the consumption of more fast food and junk food. There must be another explanation. Before you start eating Twinkies and French Fries fried in trans fat for their prostate cancer protection, let?s consider that conclusion of this study has to be scrapped for another reason too. We must assume when you eat junk food with trans fats (trans fats are man-made fat, already linked with cancer in multiple studies) those inflammatory fats get burned, removed or stored in the body. Levels of fats in the blood may fluctuate abnormally due to cancer. When you develop an aggressive cancer the cancer cells have enhanced metabolic activity and fatty acid requirements. Certain cancer cells also produce cholesterol and secrete fats. Therefore the confusing results of this study could be early signs of developing cancer, rather than the cause of it. This study is contradictory, confusing and does not come to conclusions that should dictate changes in everything we know about a cancer-protective lifestyle. With regard to trans-fats, the current study stands in contradiction with other studies on the topic. Three previous studies on either trans-fat intake or blood trans-fats have found increased risk of prostate cancer,26-28 so it is likely that the current study is the outlier. In any case, trans-fats should be avoided and for reasons not altogether clear, this study should be avoided too.29
Remember that omega-3s are essential fatty acids ? we must get them from our diet. We cannot make ALA, and we have a limited capacity to make EPA and especially DHA from ALA. These fats are crucial structural components of the brain, and omega-3 supplementation is associated with reduced risk of cardiovascular disease.30,31 However, it is not likely that omega-3 supplementation will prevent prostate cancer or any other cancer. Cancer is a complex disease, however when we consider the overall picture, we should be cautious with supplementation because even if a little is good, it doesn?t mean that high amounts are better. More than needed may not be better when it comes to omega-3 fatty acids. However, a deficiency of nutrients the body requires is never favorable for health. In conclusion, for healthy men I still recommend omega-3 sufficiency (100-200 mg/day of DHA plus 1 tbsp. of ground flaxseed for ALA). All nutrients can be harmful in deficiency or excess.
For more information on prostate cancer prevention, read my newsletter on prostate cancer and articles on cancer protection.
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