Transcript: Eggs, Choline, and Cancer
Two million men in the U.S. are living with prostate cancer, but that's better than dying from prostate cancer. Catch it when it's localized and your 5-year survival is practically guaranteed, but once it really starts spreading your chances drop to 1 in 3. "Thus, identification of modifiable factors that affect the progression of prostate cancer is something that deserves study.” So Harvard researchers took more than a thousand men with early stage prostate cancer and followed them for a couple years to see if there was anything in their diet associated with a resurgence of the cancer, such as spread to the bone.
Compared to men who hardly ate any eggs, men who ate even less than a single egg a day had a significant 2-fold increased risk of prostate cancer progression. The only thing worse was poultry consumption. Up to 4 times the risk of progression among high-risk men. They think it might be the cooked meat carcinogens—the heterocyclic amines that for some reason build up more in chicken and turkey muscle than in other meats.
But what about the eggs? Why would less than once-a-day egg consumption double the risk of cancer progression? It may be the choline. A plausible breakfast mechanism that may explain the association between eggs and prostate cancer progression is high dietary choline. Egg consumption is a determinant of how much choline you have in your blood, and higher blood choline has been associated with a greater risk of getting prostate cancer in the first place. So the choline in eggs may both increase one's risk of getting it, then having it spread, and also having it kill you.
Choline intake and the risk of lethal prostate cancer. Choline consumption associated not just with getting cancer and spreading cancer, but also a significantly increased risk of dying from it. Those that ate the most had a 70% increased risk of lethal prostate cancer. Another recent study found that men who consumed 2 and a half or more eggs per week—that's just like one egg every three days--had an 81% increased risk of lethal prostate cancer. Now it could just be the cholesterol in eggs that's increasing fatal cancer risk, but it could also be that choline.
Maybe that's why meat, milk, and eggs have all been associated with advanced prostate cancer, because of the choline. In fact, choline is so concentrated in cancer cells that if you follow choline uptake you can track the spread of cancer through the body. But why may dietary choline increase the risk of lethal prostate cancer? Remember, dietary choline is converted in the gut to trimethylamine, and so the Harvard researchers speculated that the TMAO from the high dietary choline intake may increase inflammation. This may promote progression of prostate cancer to lethal disease.
In the New England Journal of Medicine, that same Cleveland Clinic research team that did the famous study on carnitine repeated the study, but this time instead of feeding people a steak, they fed people some hard-boiled eggs. Just as they suspected, a similar spike in that toxic TMAO, so it's not just red meat. And the link between TMAO levels in the blood and strokes, heart attack, and death was seen even in low-risk groups like those with low-risk cholesterol levels. Thus eating eggs may increase our risk regardless what our cholesterol is, because of the choline.
It's ironic that the choline content of eggs is something the egg industry actually boasts about. And the industry is aware of the cancer data. Through the Freedom of Information Act I was able to get my hands on an email from the executive director of the industry's Egg Nutrition Center to an American Egg Board executive talking about how choline may be a culprit in promoting cancer progression, "Certainly worth keeping in mind as we continue to promote choline as another good reason to consume eggs."
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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