Fish oil rich in omega-3 fatty acids have long been encouraged by doctors as supplements to support heart and joint health, among other benefits. But the supplements have a dark side. Michigan State University Researchers found it induced severe colitis and colon cancer in mice.
Jennifer Fenton, a food science and human nutrition researcher at MSU led the research that supported the need to establish a dose limit for docosahexaenoic acid (DHA), one of the omega-3 fatty acids present in fish oil, particularly for people suffering from chronic conditions such as inflammatory bowel disease (IBD).
“We found that mice developed deadly, late-stage colon cancer when given high doses of fish oil,” Fenton said. “More importantly, with increased inflammation, it only took four weeks for the tumors to develop.”
The study findings, published in the October, 2010 issue of Cancer Research, support a growing body of literature implicating harmful effects of high doses of fish oil consumption in relation to certain diseases.
The MSU researchers found an increase in the severity and an aggressive progression of the cancer not only in the mice receiving the higher doses, but also in those receiving lower doses of DHA. The researchers observed the mice were prone to inflammatory-like bowel disease; inflammation is an important risk factor for many types of cancers, including colon cancer and prostate cancer.
The findings were surprising to the researchers who initially hypothesized DHA-enriched fish oil would decrease the cancer risk in the animal models. DHA has been shown in previous studies to have some anti-inflammatory properties.
“We actually found the opposite. These mice were less equipped to mount a successful immune response to bacteria that increased colon cancer tumors,” Fenton said.
Colon cancer rates in the United States are high compared to other nations. The National Cancer Institute estimates that one in 20 people of either sex will be diagnosed with colon cancer during their lifetime.
Individuals with IBD diseases, including ulcerative colitis and Crohn's disease, have an increased risk of developing cancer of the intestinal tract, and when the cancer metastasizes it can be fatal.
Fenton cautioned that people may not need to avoid fish oil entirely as it does have some known benefits. However, individuals already receiving enough omega-3 fatty acids through a well-balanced diet have no need for adding supplements which could increase their risk. But the research community also believe that a substantial number of people are dangerously omega-3 deficient.
The challenge is “with fish oil, we don’t know yet how much is appropriate,” she said.
As such, academics and the food industry have called for establishing dietary guidelines for omega-3 consumption. To accomplish this, Fenton and colleagues plan future tests of omega-3 fatty acids in people with IBD to determine how these findings correlate to human populations and what, if any, amount is safe.
Lynette Summerill is an award-winning writer who lives in Scottsdale, Arizona. In addition to writing about cancer-related issues for EmpowHER, she pens Nonsmoking Nation, a blog following global tobacco news and events.
Add a Comment13 Comments
Hi, excess of anything is bad. If we see around us everything is having some positive points also negative points. If we observe fish oil then it is been great help to many people in the area of reducing lower blood pressure, improving eye health and reducing the risk of heart disease. While talking on this research I don’t believe that a mice has the same power of immune system like human.February 6, 2013 - 1:49am
"Fenton cautioned that people may not need to avoid fish oil entirely as it does have some known benefits". This is the kind of comment which turns the public against scientific studies as seen by comments.April 17, 2011 - 8:37am
This is just "political science" to get funding for next grant! I think after reading 6 times it is irresponsible reporting - bad! Even further, bad science to extrapolate from mice metabolism to that of humans. In an ideal world we humans would eat a balanced diet, but many do not. Judicious guidance can be a help to encourage the public to counter as noted a reduction in "deficiency of omega 3 oil in our diets".
The last time I heard, fish oil had high amounts of vitamin A, which nearly any health-concious person knows can be very toxic in high amounts. A woman that I know was being treated for suspected liver cancer. Then they found she didn't have cancer and the doctors were scratching their heads. She started brainstorming with family members and someone mentioned that she had started taking fish oil (she has some heart trouble) and was taking a little extra. She stopped the pills and the trouble went away. Bottom line, take no more than the recommended daily dose (or even less) unless your doctor tells you otherwise and you'll probably be okay.April 12, 2011 - 7:36am
Do mice eat fish? I would think fish oil would be a foreign substance to most mice. Probably not a good indicator of likely effects on humans.April 2, 2011 - 11:16am
Hard to know whether it's bad research or just bad reporting. Is the reporter saying that ALL people should be cautious about fish oil supplements, or ONLY those who have a condition such as Crohn's disease or IBD? (And if you have one of those, you are most certainly aware of it.) Did all of the mice in the study have these conditions, or was there a control group of mice without them? Is there a risk that fish oil supplements would cause or accelerate colon cancer development in an otherwise healthy person, one who doesn't have Crohn's or IBD? The article is not clear. Attention Editor! Do you not have anyone to copy-read your copy for clarification?March 12, 2011 - 11:21am
Hmmm...bad research or bad reporting? I read through this twice to be sure, and I think it is just bad reading on your part. You seem to have missed a great deal of information and, to a greater extent, the entire point. Try reading it again...slowly.March 13, 2011 - 12:39pm
I WOULD HAVE AGREE THAT TO MUCH OF ANYTHING WILL CAUSE HARM .I THINK IF A PERSON IN THERE RIGHT FRAME OF MIND THAT TAKE ANY TYPE OF SUPPLEMENT WILL, AND SHOULD TAKE THEM IN MODERATION.I THINK THAT WE ALL KNOW THAT MORE ISN'T ALWAYS BETTER.I THINK IT IS JUST COMMON SENSE YOU HAVE TO TAKE THESE SUPPLEMENTS AS THEY WERE MEANT TO BE TAKEN.IT ONLY TAKES A HANDFUL OF PEOPLE TO HAVE THE GOVERNMENT TO START TELLING WHAT WE CAN AND CAN NOT TAKE .I DON'T NEED ANYONE TO REGUALATE WHAT I PUT IN MY BODY.I BELIEVE THAT I HAVE THE COMMON SENSE TO KNOW WHAT'S GOOD AND BAD FOR ME WITH A DOCTORS ADVISE.DOESN'T THE GOVERNMENT HAVE ENOUGH ON THERE TABLE AS IT IS ???March 10, 2011 - 10:29am
I agree that the methodology of this study is suspicious.
I tend to be skeptical of supplements in general. Humans evolved to eat foods in their natural context--fish oil in fish, phytochemicals in plants in the natural concentrations and mixes in which they occur. When you isolate and refine individual components of a food, you risk overdosing on one component of the food. You also often miss out on positive interactions--one ingredient may enhance the absorption of nutrients, or may block adverse effects of an excessive dose of some other chemical. Refining foods and processing them to concentrate certain ingredients both minimizes these positive interactions and increases the risk of something harmful happening.
I wouldn't give up on fish; just eat whole fish. But I would agree that, even without this study, fish oil pills, like most pills, in my opinion, are best avoided.March 9, 2011 - 1:33pm
WHY IS IT EVERY TIME WE FIND SOME THING THAT MAY BE GOOD FOR US AS HUMANS THEN TEN YEARS LATER WE ARE TOLD THAT IT NOW CAUSES CANCER.I SOMETIME WONDER IS SOME OF THE STUFF PUBLISHED IS FACTUAL OR DOES SOME OF THESE RESEARCHER HAVE SOME SPECIAL INTEREST.I SECOND IT'S GOOD FOR YOU AND IN A BLINK OF AN EYE IT ISN'T.I HATE THE SCARE TACTIC THAT THE MEDIA USES FOR THERE OWN SPECIAL INTEREST.PLEASE STOP ALL OF THIS NOW.DO WE REALLY KNOW FOR SURE WHAT'S GOING ON WITH THE FISH OIL....STOP NOWMarch 9, 2011 - 10:58am
The simple answer to your question is that regulations governing how much testing must be done and for how long those tests run have been weakened to the point of non-existence so companies can rush products to market without comprehensive testing to improve their bottom lines. Further, fish oil is considered a supplement, over which there is virtually no testing for safety or effectiveness. The general population is the study group for all these products, and it takes about 10 years for the effects to start showing up in the population.March 13, 2011 - 12:36pm