Tuesday, November 04, 2008

Coffee and cancer

I recently had an armchair expert tell me that french press style coffee vs a filtered coffee preparation method increases your risk of cancer. [Don't confuse french press coffee for the biological apparatus]. This person was foggy on the details but indeed got rid of their Bodum(tm). Personally I find coffee from a french press tastes superior, but then again, I'd drink it off a dog some mornings. Some googling revealled one source of the idea that unfiltered coffee increases your risk of cancer the source they cite is an article that shows increased homocysteine levels in drinkers of unfiltered coffee vs NO COFFEE. (no coffee?!?!) Homocysteine itself is not directly derived from your diet, however, high levels in the blood are indicators for high risk of heart attack and stroke, and possibly cancer. The thought was that filtering coffee removed what the authors assumed was causing the rise in homocysteine levels. Turns out filtering coffee doesn't change the fact that drinking coffee raises homocysteine levels.
To me this is a good example of something I see often, that is, cancer research NOT serving the public who funds it. If this is the crappy way that the public is informed about cancer research I'm surprised it still is funded. Someone gets rid of their french press because their concerns for their health based on the mainstream medias reporting of an incorrect assumption in the literature. What is also strange is that the damage is done. I think I would have a hard time convincing this person that their french press coffee is no worse for them.
Also I think there is a leap of logic here that I have heard is similar to the leap in logic made for the statin class of drugs. That is that since higher homocysteine levels correlate with higher risk of cancer (let's assume the one article I found linking the two is correct), then homocysteine is a cause of cancer. An indicator is not necessarily the cause but is merely associated with increased risk.
Also it may be that coffee raises cancer causing homocysteine levels by an appriciable amount, however, other factors associated with coffee drinking may result in an overall reduction in cancer incidence. So again even if homocysteine causes cancer, coffee may not.
Of course, perhaps coffee has so taken over control of my thought processes that I am in denial.


The Doc said...

Actually, this is also a topic quite near to my heart - a follow up study involving a very closely followed group of young people for 24 hours and giving them a dose of coffee (http://www.nature.com/ejcn/journal/v58/n9/abs/1601957a.html) appeared in my thesis and I'm one of the authors on that paper, and incidentally, one of the clinical study patients. It's the only study which directly connects the homocysteine with the coffee. In the study we used instant coffee (albeit a very strong one) for control purposes, and found that it acutely raises homocysteine. We then showed that the molecule in coffee which we thought was responsible (trigonelline) wasn't the nasty agent we thought it would be.

Homocysteine is an interesting molecule. It's so tightly linked to CVD that it's impossible to really understand it unless it's a causative agent. That being said, no-one's particularly nailed down HOW it's a causative agent. A few studies have popped out and concluded that reducing it (by folate and B12 - which is only half a story) after a CVD event has no real effect on further events, but they all suffer from the problem that the damage which may have been caused by homocysteine may have been done some time earlier, and by the time they intervine, it's too late.

I must confess, during my thesis, I never really read much about Hcy being connected to cancer - although I was so damned focussed on CVD and renal problems that I guess I never looked.

Coffee consumption has been linked to cancer protection, I believe. I don't think homocysteine levels will affect your risk of cancer that much... it'll knock you off via your circulatory system first.

Anonymous Coward said...

Another interesting study about coffee that appeared this week showed that even moderate amounts can harm the fetus . This contradicts previous study which suggested that pregnant women could drink small amounts of coffee without worrying.

Anonymous said...

Unfortunately prostate cancer symptoms are not seen in the early stages when it can be curable. Decrease in food intake, lack of hunger, weight loss, softening of bone are the symptoms seen in advanced stages.

Rob said...

@ the doc.
If you lower the levels of homocysteine it doesn't help, then how is it a causative agent? Again, it reminds me of statins. Great at lowering bad cholesterol, with no significant impact on mortality. To me that suggests they are just indicators that are correlated.
Perhaps you are right if homocysteine levels were lowered before CVD it would help, but until this is shown then it is difficult to say. No? That coupled with the uncertainty of where homocysteine levels in the blood are originating, makes the causative agent idea pretty premature.

The Doc said...

The main concern with the studies is that homocysteine is formed in one set of reactions (methylation by at least 300 different enzymes) - but there are then three alternate destinations for that homocysteine. Roughly half of the homocysteine is destroyed and converted into cysteine via cystathionine B-synthase, and vit B6, largely in the liver (tho not exclusively).

A quarter of it is remethylated by B12 and folate in pretty much every cell in your body. The last quarter is remethylated by an enzyme called Betaine-Homocysteine Methyltransferase, which makes up about 1-2% of ALL the soluble protein in your liver!

All those studies got rather small (but significant) drops in Hcy by treating with folate and B12. They completely ignored 75% of the whole pathway... despite a LOT of evidence that BHMT actually does all the grunt work of Hcy turnover... with folate/B12 taking up little bits of slack when you eat too much.

And to respond, there is actually quite a bit of evidence that lowering homocysteine early does reduce the risk of CVD - although most hyperhomocysteimia (spelling?!) is a result of genetic disorders which are usually treated by doctors via B12/folate. The betaine story has been largely ignored.