By Sarah A LoBisco, ND
I just posted July’s 2013 Top Holistic Health Reads on my website. It includes summaries regarding: the finding of a fat gene, the use of green tea for a genetic disease in children, the link between the gut and autism, more disability even though there’s longer life stats in US, the emotional impact of mammograms, and the link of statins to breast cancer.
I hope you can find the time to skim through the headlines and decide if you want to dip deeper to learn more via reading the excerpts or going to the source links.
On this blog, I’d like to highlight the TOP NUTRIGENOMIC STORY of July 2013, the touted fish oil-cancer connection.
Below are some excerpts from a few articles that explain how the study was flawed and some conclusions we can trust (emphasis mine).
Data Used was From the SELECT Study
When you use data from a study to extrapolate what was not being controlled for to test, yikes!! Here’s a summary of how this leads to misinformation:
The pedigree of the study source is impressive. It was published in the Journal of the National Cancer Institute and was conducted by researchers from the Fred Hutchinson Cancer Center in Seattle, WA.1 Yet, the data they used is from the much maligned Selenium and Vitamin E Cancer Prevention Trial (SELECT). That is the real problem.
The SELECT study was a very large clinical study that attempted to determine whether vitamin E could prevent prostate cancer. Previous studies had shown 50 IU of vitamin E was protective against prostate cancer, but the SELECT study chose to use 400 IU of synthetic vitamin E (dl-alpha-tocopherol) at a dosage of 400 IU. Results showed that the subjects taking vitamin E alone had a 17% higher risk of prostate cancer compared to the control group.
In the new analysis, researchers measured the levels of fats in the blood (plasma phospholipids) and concluded that men with the highest concentrations of EPA, DPA and DHA-three fatty acids derived from fish and fish-oil supplements-had an increased risk of prostate cancer. Specifically, they reported a 71 percent increased risk of high-grade prostate cancer; a 44 percent increase in the risk of low-grade prostate cancer and an overall 43 percent increase in risk for total prostate cancer in a subset of patients with the highest level of these omega-3 fatty acids.
Important considerations of this data are the following:
• This study is not consistent with other studies (discussed below)
• The study did NOT include information or documentation of fish or fish oil intake in the study group. It was NOT set up initially to evaluate these factors, hence its relevance is not as significant as studies designed to specifically determine the impact of omega-3 fatty acids on prostate cancer risk.
• There is no evidence that anybody in this study took fish oil supplements or even ate fish.
• In usual circumstances, plasma levels of EPA and DHA reflect very recent intake and are considered a poor biomarker of long-term omega-3 intake.
• Patients with prostate cancer may have only recently increased their fish and/or fish oil consumption.
• Fish and fish oil ingestion produces a big rise in plasma omega-3 levels in about 4.5 hours and washes out around 48 hours.
• The data may reflect cancer activity rather than a causative association. Without dietary history or documentation of fish oil use there is no way of knowing.
Lastly, the following statement by the authors suggests that they may have significant bias:
“There is really no evidence that taking dietary supplements is beneficial to health, and there is increasing evidence that taking high doses is harmful.” Such a statement shows a clear axe to grind in light of a great deal of scientific evidence on the value of dietary supplementation.
A Closer Look at the Reported Results
Let’s take a closer look at the reported results to see if things add up. The bottom line is that they do not. Let’s first take a look at the blood levels of EPA+DHA – the major forms of long-chain omega-3 fatty acids found in fish oil supplements. As Table 1 shows the levels are quite similar among the groups. These blood levels of EPA+DHA are actually quite modest and do not reflect huge levels of fish or fish supplements being consumed. The average EPA+DHA plasma level for men is generally approximately 4%. So, the levels reported here are typical, but a little lower than normal and the ratio of EPA to DHA is also a little lower as well.
Murray, M. How a SELECTed Bad Study Became Big News. GreenMedInfo.com. July 12, 2013. http://www.greenmedinfo.com/blog/how-selected-bad-study-became-big-news?utm_source=GreenMedInfo+Weekly&utm_campaign=9d62297a1b-Greenmedinfo&utm_medium=email&utm_term=0_62bb7ef31e-9d62297a1b-86825417
More Fish Oil Study Refute
What we can be sure of is that association does not prove cause and effect. If this had been an intervention design study, where half the participants got fish oil and half didn’t and they were followed for 20 years to see if they got prostate cancer, then you can say pretty definitively that they are connected. Bottom line, this type of study does not prove cause and effect. If I did a study on sunrise and humans waking up, I would find 100% correlation, but that doesn’t mean that the sun came up because you woke up. Correlation, yes; causation, no.
Another problem with the study is that the researchers did not address whether the men who were studied got their omega-3 fatty acids from eating fatty fish or from taking supplements. Also, there was no regard for their health status before starting the study. Did they start using fish oil as a therapy once diagnosed with prostate cancer or had they been taking it all along?
And what about the myriad other factors that can lead to the onset and progression of cancer, such as how lifestyle affects genetics? Smoking, nutrition, exercise, environmental toxicity, stress: none of these things were taken into account. It is too simplistic to reduce a disease as complex as cancer down to one trigger. In fact, perhaps we should be asking if these men were exposed to toxins and heavy metals from eating mercury-containing fish, which can cause cancer. Or did the men smoke or drink to excess? Was there a history of cancer in the family? What was their personal health history prior to diagnosis? Were they overweight or obese, and did they have other symptoms of diabesity?
Another major flaw with this study’s design involves the way the researchers got their data. They analyzed blood plasma instead of red blood cells. And they did so with one single blood draw! The conclusions would have been stronger and more reliable had they used red blood cell samples, because those provide a more accurate assessment over the long term (plasma tends to provide only a short-term picture). Because the research was based only on samples of a single blood draw, the red blood cell analysis would have given a better picture of long-term omega-3 intake (a couple months of eating salmon, for example, instead of what happens in the body after a single meal). That’s why I suggest people use the omega-3 index test, which measures levels from within the red blood cells.
Hyman, M. Can Fish Oil Cause Prostate Cancer? Drhyman.com. July 26, 2013. http://drhyman.com/blog/2013/07/26/can-fish-oil-cause-prostate-cancer/#close
Confounding Factors in Prostate Study Summary- Sounds Fishy to Me!
Confounding Factors Ignored
Another problem with studies looking at correlations only, is that the factor you’re looking at
may only be a minor player, or completely irrelevant, compared to other factors. For example, in this case:22
• 53 percent of the subjects with prostate cancer were smokers
• 64 percent of the cancer subjects regularly consumed alcohol
• 80 percent of the cancer subjects were overweight or obese
According to a 2011 study published in PLoS One,23 aggressive prostate cancer was associated with obesity. More recently, a cohort study published in Cancer Epidemiology, Biomarkers & Prevention24 in April of this year found that men who were overweight or obese increased their risk of prostate cancer by 57 percent–a percentage that falls right smack in the middle of that 44-71 percentage range attributed to high DHA serum levels in the featured study. And this association between obesity and prostate cancer held for all cases– low-grade and high-grade, early stage and late, nonaggressive and aggressive prostate cancer.
Mercola, J. Absurd Study Claims Omega-3 Fats Raise Prostate Cancer Risk. Mercola.com. July 31, 2013. http://articles.mercola.com/sites/articles/archive/2013/07/31/omega-3-fats.aspx?e_cid=20130731_DNL_art_1&utm_source=dnl&utm_medium=email&utm_content=art1&utm_campaign=20130731
The Bottom line to me:
The use of fish oil for a therapeutic trial should be studied using a proper trial with a population that truly tests the intervention at hand. Data should not be extrapolated from a prior study. It also supports individualized medicine.