Friday, February 17, 2012

Another Study Hints At increased Cancer Risk From Omega-3

This study investigated whether taking B vitamins or omega-3 fatty acids could reduce the risk of cancer. It found they didn't:

B Vitamin And/Or Omega-3 Fatty Acid Supplementation And Cancer, Archives of Internal Medicine, February 2012
"We found no beneficial effects of supplementation with relatively low doses of B vitamins and/or omega-3 fatty acids on cancer outcomes in individuals with prior cardiovascular disease."
Participants (n=2501) took supplements for 5 years. They were divided into 4 groups:
  1. B vitamins: Folate (0.56 mg) and Vitamin B6 (3 mg) and Vitamin B12 (0.02 mg)
  2. Omega-3 fatty acids: EPA (400 mg) and DHA (200 mg)
  3. B vitamins plus Omega-3s
  4. Placebo
Researchers did, however, find a statistically significant increased cancer risk among women taking the omega-3s; a 3-fold greater risk of developing cancer (HR 3.02) and an over 5-fold increased risk of dying from cancer (HR 5.49).

The lead investigator, Dr. Valentina Andreeva, said:
"People should be very careful when deciding to self-medicate with these dietary supplements because they are active substances. The findings need to be confirmed and should be interpreted with caution, but there is some indication that they might have adverse effects. Taking these supplements without a physician's advice and over the long term might not be a good idea."
- Heartwire
Five years isn't long for cancer to develop and progress to the point of death, so the cancer was probably there already, small and undetected. If anything, the omega-3 may have hastened its progression.

This adds evidence to the possible connection between omega-3s and cancer. So far I've seen it linked to prostate cancer:
How Much Fish Oil Is Good?
Omega-3 Fatty Acid DHA Found To Increase Risk For Prostate Cancer

And colon cancer:
Fish Oil, Colitis, And Cancer

The mechanism? Who knows. Maybe a reduction in natural killer cells:
Can Omega-3 Fatty Acids (Fish Oil) Predispose Someone To Cancer?

Or maybe it's something about the manufacture of these supplements. How do you keep all that highly processed fish oil from going rancid?


Angela and Melinda said...

OK, I'm curious. You say that you don't recommend a vegan diet as healthy in general. So what do *you* eat that's not vegan, or are you actually a vegan? I'm really curious--I do NOT mean this in a confrontational way!!!!!

Bix said...

I'm not a vegan. I like a little salmon once in a while. As I read it, Dr. McDougall says he isn't a vegan; he likes a little turkey on Thanksgiving :) Even Dr. Campbell says, to the effect of, "Go for the 95%."

Bix said...

As regards this post, I think it's the fish oil capsule that's suspect. It's an extracted, processed, filtered, concentrated substance that has probably been subjected to heat and chemicals.

Getting omega-3 in foods ... greens, fish, walnuts, flax ... is healthy as all get out, no?

As soon as you say something is good, people eat a lot of it or take it in a pill. Likewise, if you say it's not a good idea to eat a lot of something, people banish it from their diet. Either of these extremes, IMHO, is unhealthful.

I think (as if it matters) that a diet which excludes all animal products is not as good as a diet that includes some.

Laurie Endicott Thomas said...

Dr. Campbell's research showed that even small amounts of animal-based food in the diet was associated with a small increase in the risk of death from chronic disease. There's no safe level of intake. He has suggested that the optimal amount of animal-based food in the diet seems to be zero.

The increased risk of cancer associated with a high intake of omega 3 fatty acids is most likely due to immune suppression from omega 3 overdose, not to the processing of the capsules.

Angela and Melinda said...

Thanks for the good info, Bix! I agree w/ you re supplements vs getting healthy substances from food, though of course one always has to wonder about how the food was raised and how recently it was harvested/processed. With flax in particular, I had the impression that flax seeds/oils had to be kept cold all the time or else they would become rancid. Or is that only true of the oil, but not the seeds? Also, if flax is cooked in a recipe--baked, stir-fried, boiled--does it lose its efficacy in terms of Omega-3?

Bix said...

I was in a health food store a few months ago and the woman in front of me purchased all the flax seed they had on their shelves. There was a mountain of flax on the conveyor belt! I wondered what she would do with it all. It occurred to me that she has a belief in some, I don't know, extra-ordinary property of flax. And it occurred to me, as it often does these days, that her belief may be the stronger source of any effect of flax (compared to a measurable? effect of flax itself).

Anyway, your comment just reminded me of that story. I don't mean to sully flax's reputation ... in that it's a good source of the shorter-chain, plant-based omega-3. And, yes, as a food with a lot of polyunsatured fat, it's best to keep it cold, out of direct sunlight, to decrease oxidation ... both the oil and the seed, although the oil is more vulnerable.

I would guess that heating (bake/fry/boil) does degrade some of the omega-3 fatty acids, not all.

Bix said...

"... though of course one always has to wonder about how the food was raised and how recently it was harvested/processed."

Isn't that the truth!

Claudia said...

To Laurie Endicott Thomas, where do you get vitamin B12 if you don't eat meat?