Shark Week

Hello and welcome to the Nutrition Facts podcast. I’m your host, Dr. Michael Greger. 

Now, I know I’m known for explaining how not to do certain things  (just look at my books, How Not to Die, the one I’m working on right now–How Not to Diet), but what I actually have to share with you is quite positive and boils down to this: What’s the best way to live a healthy life?  Here are some answers.

Just in time for summer fun at the beach it’s shark week here on the Nutrition Facts podcast.  Why are millions of dollars spent on shark cartilage supplements?  Here are some answers.

An assessment of “websites on complementary and alternative medicine for cancer” found that “[m]any endorse unproven therapies and some that are outright dangerous,” potentially exploit[ing] highly vulnerable patients and enrich[ing] irresponsible snake oil peddlers”—or for that matter, shark-cartilage peddlers, accounting for millions of dollars of sales every year. Why shark cartilage, of all things?

“…[I]nterest in shark cartilage as an anticancer agent arose because many people believed that sharks did not get cancer.” Why would they think such a thing? Because some shark-cartilage supplement hawker wrote a book called Sharks Don’t Get Cancer. But that’s simply not true. “Sharks do get cancer.” “…[B]oth benign and cancerous…lesions have been reported in 21 species of sharks from [more than] 9 families.”

Now, some “shark cartilage distributors insist [instead] that sharks [just] rarely get cancer,” [but] actual cancer rates in sharks have [never] been determined.” “[T]here [has simply] been no systematic tumor surveys of sharks” for them to make such a claim. But look, “even if sharks [were] less susceptible to cancer,” how can one logically jump from that to cancer patients benefiting from eating powdered cartilage from a shark?

“We know, for example, that there are [certain] proteins that allow [some bacteria to survive] in boiling hot [springs].” Uh, does that mean if we eat those bacteria we can survive boiling water, too? It doesn’t make any sense. “The illogic behind the pursuit of shark cartilage therapies has implications beyond the reduction of shark populations and the misdirection of patients to ineffective cancer therapies.” The stuff may be harmful, and I’m not just talking about the rare case of “shark cartilage-induced liver [inflammation].” Shark products can contain the neurotoxin BMAA, which I’ve talked about before. It’s been detected at elevated levels in the brains of Alzheimer’s disease and ALS patients, and may “play…a role in [the development of] neurodegenerative diseases.”

So, the “consumption of shark-fin soup may pose a significant health risk.” But what about shark-cartilage supplements? They tested 16 commercial shark-cartilage supplements, right off the shelves, and found BMAA “in fifteen out of sixteen.” But look, even if shark-cartilage supplements carry “pro-inflammatory properties, which could pose a potential health risk for consumers,” we’re talking about cancer. There are chemotherapy agents that are life-threateningly dangerous, but sometimes the benefits can outweigh the risks, when confronted with cancer. So, the question then becomes: are there any benefits to shark cartilage?

I mean, it’s not a completely wacky idea. “[C]artilage [in general] is highly resistant to invasion by tumor cells.” So, maybe there’s some “cartilage-derived anti-invasion factor.” “Less interesting alternative explanations…are” that it’s just hard for the cancer to penetrate the cartilage, or perhaps because of the poor blood supply in cartilage, cancer doesn’t consider it a particularly fertile ground. But maybe that lack of blood vessels in cartilage can be exploited. The reason that no blood vessels end up in cartilage is because cartilage cells produce angiogenesis inhibitors, blood vessel-creation inhibitors. So, maybe we can starve tumor growth by infusing these cartilage factors. What scientists do is implant tumors into the eyeballs of rabbits, so they can visualize how many blood vessels the tumor is able to draw to itself.

And, indeed: “Shark cartilage contains inhibitors of tumor angiogenesis.” “Such findings made the sales [of shark cartilage sky]rocket, [driving]…two shark species…to the brink of extinction.” But, cow cartilage does the same thing and so does human cartilage, for that matter. So, why sell shark cartilage? Well, it does sound so much more exotic, and sharks have like 10 times more cartilage per animal. One 20-foot shark could net like 50 pounds of cartilage.

Just because cartilage has blood vessel-inhibiting chemicals in it, though, doesn’t mean if cancer patients eat it, it will help them. It’s kind of like magical thinking: shark cartilage stops blood-vessel growth. “Thus, by consuming shark cartilage, humans will [somehow] be…protected.” I mean, the “shark cartilage protein molecules [would seem to be] too large to be absorbed by the gut.” It’s not like you’re injecting shark cartilage into your bloodstream through an IV.

But there was this rat study that did find that just feeding shark cartilage to animals, you could cut down on blood vessel growth within their body. Okay, but does that translate out to stopping the growth and spread of cancer? Apparently not, as “none of the shark cartilage doses tested had any retarding effect on [cancer growth]” or spread in tumor-bearing mice. But just because it doesn’t work in rodents doesn’t mean it doesn’t work in humans. To find that out, you need to put it to the test, evaluating shark cartilage in human cancer patients, which we’ll cover, next.

Yes, shark cartilage supplements carry risks, but so do many cancer treatments. The question is does it work.

When it comes to marketing “unproven cancer treatments,” “the Internet has become the Wild West. Fraudsters are…able…to take advantage of people” like never before. “Cancer Patients Find Quackery on The Web”, bemoaned the National Cancer Institute. Did you know there were “[m]ore than 200,000 documents about cancer…on the…Web”? What? When was this published? Oh, 1996. That’s just a few years after the web was born. Not to worry, though, said the author of Dr. Linden’s Guide to Online Medicine, “it takes a lot of time and money to maintain a Web page.” So, don’t worry, “the mass of information on the Internet will dwindle during the next few years as the Internet matures.”  Riiiiight. Yes, dwindling from 200,000 down to a mere quarter of a billion. And, one of the most commonly recommended “alternative cancer cures” on popular websites is shark cartilage.

“Much has been made in recent years of the mystical aura afforded [to the stuff]. Clearly, part of [it is the] visceral fear of cancer combined with a healthy respect for a creature [who] has survived [basically unchanged since] prehistoric times. It has been reported that sharks rarely get cancer,” and their skeleton is made out of cartilage, and so, “[l]ogic has led some to believe that this must be the reason for sharks’ relative health.” Not exactly sure that’s logical, but they do have a lot of cartilage. Cartilage, in general, has few blood vessels, and blood vessels are important for cancer growth, and all this “conspired to prime fraught [cancer] patients for shameful exploitation by pseudoscience and the supplement industry with the addition of just one myth” and that “sharks don’t get cancer.” But, they “do get cancer” after all. Just another “layer…of fallacious arguments,…successfully convinc[ing] desperate cancer patients to buy ineffective products.” But wait, you don’t know if it’s ineffective, until you put it to the test.

Sixty patients with a variety of advanced cancers given like a dozen scoops a day of shark cartilage, and…not a single, even partial, response was noted in any of their tumors. Ineffective with “no salutary effect on [the] quality of life.” In fact, they suffering significant gastrointestinal toxicity from the stuff, all the while the tumors progressed in all the patients.

But what’s missing from this survival graph? What happened in the control group? There was no control group. How do we know the cancers wouldn’t have progressed even faster without the shark cartilage? That’s why we need randomized, controlled trials, but there weren’t any, until the Mayo Clinic stepped up. “[A]…randomized, placebo-controlled, double-blind, clinical trial [for] [p]atients with incurable breast or colorectal carcinoma.”

“Data on a total of 83…patients [was] analyzed. And? “There was no difference in…survival between patients [getting]…shark cartilage…versus [those getting] placebo”—nor any “suggestion of improvement in quality of life.”

There was evidently a prostate cancer study, too. Only five patients were even able to complete the study, and, in all five, their cancers continued to progress unabated.

So, “Unfortunately, the claims for the benefits of shark cartilage are completely unsubstantiated by any objective data from controlled clinical trials.”

Not so fast, said supplement manufacturers. Maybe these crude commercial shark cartilage powders just don’t have high enough levels of whatever active components there may be. So, cancer patients should instead be taking shark cartilage extract pills. So, the National Cancer Institute said fine, we’ll test that too, just to make absolutely sure. And so, they funded a randomized, double-blinded, placebo-controlled trial to put it to the test.

Unlike the other shark cartilage dietary supplement studies, they used the purified extract, and “the study outcome [was] unambiguous.” It failed. The shark cartilage group lived 14 months, and the placebo group lived 15 months. So, no significant difference in survival or time to progression or tumor response rate. So, “[t]hese clinical studies [suggest] shark cartilage is not just [an] unproven…cancer remedy, [but actually a] well disproven [one].” Yet, “[d]espite [the] overwhelming evidence to the contrary, such claims persisted. For example, the huckster who started it all wrote a sequel, Sharks Still Don’t Get Cancer. Perhaps “[t]he only cure for this myth is to spread the rumor that cartilage from the noses of [such] quacks [fights cancer too].”

Anyway, if you really wanted to eat angiogenesis inhibitors, why sit down to a bowl of cartilage powder, when you could just eat an apple, or drink green tea, or turmeric, or pomegranates, berries and nuts, soybeans, flax seeds, broccoli—all of which have been shown to have anti-angiogenic effects.

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need – plus links to all the sources we cite for each of these topics.

Be sure to check out my new How Not to Die Cookbook.  It’s beautifully designed, with more than 120 recipes for delicious, plant-based meals, snacks and beverages.  All the proceeds from the sales of all my books all go to charity.  I just want you to be healthier.  

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There’s no ads, no corporate sponsorship.  It’s strictly non-commercial.  I’m not selling anything. I just put it up as a public service, as a labor of love – as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts.  I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.