Antioxidants & Cancer: Read the studies carefully

When I first saw headlines of articles about how “could help spreading growth of cancer cells” by antioxidants, I initially thought, oh boy, another sacred cow of the nutrition scolds takes in on the chin. My first idea about this post was to point out how we jump on fads (acai berries) with the slimmest of scientific evidence, following by food marketers rapidly jumping on the bandwagon so they can label some product (probably otherwise bad for you) with the latest superfood miracle cure.

But as I did a little more digging into the articles I began to switch my thoughts more to using this example to repeat my warnings about reading the popular press and how it may distort whatever science is being studied. After digging through numerous of the popscience articles I finally found the link to the Nature article, certainly a respectable journal (although also publishing a defense of alternative medicine, already denounced by Orac, so maybe their woo has sneaked through). Anyway, as usual the actual science article is hidden behind a paywall so all I could access with the abstract and a couple of charts revealing the actual data. The abstract says:

Solid cancer cells commonly enter the blood and disseminate systemically, but are highly inefficient at forming distant metastases for poorly understood reasons. Here we studied human melanomas that differed in their metastasis histories in patients and in their capacity to metastasize in NOD-SCID-Il2rg−/− (NSG) mice. We show that melanomas had high frequencies of cells that formed subcutaneous tumours, but much lower percentages of cells that formed tumours after intravenous or intrasplenic transplantation, particularly among inefficiently metastasizing melanomas. Melanoma cells in the blood and visceral organs experienced oxidative stress not observed in established subcutaneous tumours. Successfully metastasizing melanomas underwent reversible metabolic changes during metastasis that increased their capacity to withstand oxidative stress, including increased dependence on NADPH-generating enzymes in the folate pathway. Antioxidants promoted distant metastasis in NSG mice. Folate pathway inhibition using low-dose methotrexate, ALDH1L2 knockdown, or MTHFD1 knockdown inhibited distant metastasis without significantly affecting the growth of subcutaneous tumours in the same mice. Oxidative stress thus limits distant metastasis by melanoma cells in vivo.

Now of course even this abstract has a fair amount of science-y jargon, but with a bit of basic knowledge it’s not too hard to parse, but let’s contrast this with a report about this article in a popular press article whose headline starts with “Horrifying findings …”:

To be clear, the research doesn’t suggest that antioxidants cause cancer. Instead, it finds that already present cancer will grow far more rapidly in an environment rich with antioxidants.

The first mistake all the popular press articles have is simply using the term ‘cancer’. This is a very imprecise umbrella term that covers hundreds of more specific cellular conditions, each one with different prognosis and treatment. The referenced article only dealt with melanoma, a particular nasty type of abnormal cellular growth, but only one of many. So, inappropriately, the popular press articles expand the narrow scientific conclusion to cover all cancers, even something like prostate which is completely unrelated.

Second, it’s an interesting turn of phrase to say “will grow far more rapidly”. While technically within the context of the actual article the popular press article is implying a causation link, which is not actually what the science says.  They’re actual referring to “inefficiently metastasizing melanomas“. Now metastasizing and “growing” aren’t very much the same thing (“spreading” would be better but still imprecise term for the non-scientific). And some process that in the absence of an outside chemical that works poorly and then works a little better in the presence of that chemical is hardly “grow far more rapidly”.

Now I expect Orac to weigh in on this topic soon enough and as both a cancer researcher and surgeon, plus I’m sure he can read the entire article in Nature, he can address the scientific points much better than me,  But I still think I’m qualifying to raise some cautions/skepticism to reading too much into the popular press accounts.

Another issue that the lay public doesn’t understand is science reported in any study is always provisional. Science is a process, not just a bunch of facts. And it is a self-correcting process. I’m sure there will be critics of this study who will try to find its flaws. Honest factual debate is a good thing in science because that is how results get verified or discarded, not just rhetorical debate of the usual political kind. Perhaps you remember headlines about faster-than-light neutrinos; now that would be an astonishing discovery so naturally lots of scientist dug into every detail of that study, and, guess what, the results were wrong due to a loose cable. A finding has to withstand scrutiny and has to be replicated before it gains any weight of evidence, often over even hundreds of studies and decades. A tantalizing study is a nice starting point, but not an end point. Several of the popular press articles hint at (but not citations) other studies with similar or at least related conclusions. Assuming popular science writers have access to PubMed (everyone does, free access) and maybe some subscriptions to journals (many do, I don’t) it wouldn’t take much time to provide some references, both confirming and denying this latest study.

In the nutrition arena we are constantly seeing dogma established and then later completely discarded. Why did the dogma spread so quickly on such thin data? Some minimal, possibly ambiguous, and quite probably wrong (like the Mediterranean diet nonsense) get thrown around in the echo chamber of popular press and then winds its way into advocacy sites (the various naturalist sites) and then even into woo sites (foodbabe, I’m looking at you). Every step further from the science allows more and more misinterpretation where eventually any statements at all are pure mush, almost always completely wrong (you can still find plenty of nutrition sites denouncing dietary cholesterol as cause of elevated serum cholesterol levels when this has been thoroughly debunked).

So even though the conclusions of this study tend to match my biases (no such thing as “superfoods”, just popular nonsense) I still suggest caution. Plus how many thousands of ways will the public misinterpret even the accurately reported results? Are blueberries going to now go out of fashion, even though nothing in this studies could possibly justify that fear for any more than a few percent of the population? Or will all the “natural” food sites just denounce this study as more indication that science is stupid and somehow “faith” is a better way to decide what you put in your mouth?

I think a lot of the total garbage one reads about nutrition is partly due to the steady decline of science literacy in the general public and the anti-science attitude of the rightwingnuts and carbon polluters and creationists. The public deserves better. You don’t need an MIT degree to be a more critical reader, esp. about a finding that might (or might not) actually affect you.

There’s not much you can do about intelligence (you’ve got what you’ve got) but there is a lot anyone can do about ignorance, which is completely curable with actually paying attention and doing some digging. The Internet is a wonderful tool, far better than anything ever created before, for making information available – it’s just too bad most of it a garbage and too few people know how to look at the avalanche of information critically.

Advertisements

About dmill96

old fat (but now getting trim and fit) guy, who used to create software in Silicon Valley (almost before it was called that), who used to go backpacking and bicycling and cross-country skiing and now geodashes, drives AWD in Wyoming, takes pictures, and writes long blog posts and does xizquvjyk.
This entry was posted in comment and tagged , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s