All:
I came to this conclusion last week, and have been doing my usual thing of putting off posting until I have the time to go into it properly, which of course I never do ... and this is too important.
(1) has been posted both here and on sci.l-e, in the context of debating which forms of thiamine are superior to others and whether very-high-dose thiamine can exert similar effects as benfotiamine. But the actual, central import of the study was basically ignored or downplayed by everyone (myself included) in the context of the debate:
My attention was drawn back to this study when listening to an episode of CBC's Ideas podcast entitled "Science at the Summit," featuring prominent Canadian scientists, including Tak Mak, discoverer of the T-cell receptor. Beginning at about 0:24:30, Mak explained (in very simple terms) how and why his team is now going after novel cancer therapeutics on the basis of the new understanding of the "Warburg effect" -- the well-known phenomenon that many cancers are hypoxic, engaged in furious non-oxidative metabolism at the expense of oxidative phosphorylation as their energy source. This observation is consistently invoked by a variety of sales people and/or cultish devotees of various pseudoscientific diets, supplements, and quack cancer cures, as proof that cancer is caused by or relies upon either an acid metabolism or a lack of oxygen in the circulation -- which, of course, their supplement/therapy can reverse (for which assertion, in turn, they offer no good evidence).The effect of thiamine supplementation on tumour proliferation was demonstrated by in vivo experiments in mice with the ascites tumour. Thiamine supplementation in doses between 12.5 and 250 times the recommended dietary allowance (RDA) for mice were administered starting on day four of tumour inoculation. We observed a high stimulatory effect on tumour growth of 164% compared to controls at a thiamine dose of 25 times the RDA. This growth stimulatory effect was predicted on the basis of correction of the pre-existing level of thiamine deficiency (42%) [which evidently results from the cancer's gobbling up of high levels of thiamine, and "which has been observed for decades in cancer patients"] , as assayed by the cofactor/enzyme ratio.
Instead, Mak briefly explained that, rather than somehow preferring to use the very inefficient lactic acid pathway as their route to generate ATP instead of OXPHOS, these cancers are instead stuck using it, because of what they really need: they are trading off the wasted energetic potential of glucose, in favor of feeding glucose carbon into the pentose phosphate pathway to maximize nucleic acid ribose synthesis, and thereby maintain the massive production of proteins, DNA, and "novel fatty acids" that they need to maintain their runaway proliferation.
Of course, activation of the pentose phosphate shunt is exactly the route by which benfotiamine reduces the formation of intracellular oxoaldehydes -- and thereby, AGE -- in diabetes.
Without analyzing this in detail, I'll point everyone to the references appended. Several lines of evidence -- the high activity of thiamin-dependent, pentose-phosphate-activating transketolase-1 in many cancers, and its predictive role in poor disease prognosis; the efficacy of antithiamin chemotherapeutic agents against a range of cancers; weak evidence showing an apparent link between thiamin insufficiency and reduced cancer risk; and the supplementation study (1) -- all support this idea, and therefore suggest that, while you clearly don't want to go around frankly thiamine deficient in order to avoid cancer, having a chronic oversupply of bioactive thiamine (from benfotiamine, or any other source) likely creates a permissive environment for these cancers.
By strange coincidence, I see that Kismet has just very intelligently raised the question of the evidence basis for benfotiamine supplementation in normal, healthy people. The answer, of course, is that ultimately there isn't one: indeed, there is no really good evidence for any kind of supplementation in normal, healthy people, except for correction of frank nutrient deficiency. In my 2004 CR Society Conference lecture on supplementation, I classified benfotiamine as a 'Tier III' supplement: one for which there was some limited, speculative evidence of possible anti-aging benefit (in this case, based on the results of studies in diabetic animals and humans, and the speculation that it might have similar benefits in healthy folk during postprandial glucose surges, in response to dietary AGE, or in other risky metabolic states), and reasonably good evidence for lack of harm (based on extensive animal studies, some limited human clinical trials, and decades of use as a regulated and monitored 'drug' in Europe).
This was enough for me to take it, and to think it reasonable for others to do so, too; indeed, some of you are likely aware that I am the single person most logistically responsible for the initial availability of benfotiamine as a dietary supplement in North America, and (with the likely de facto exception of Michael Brownlee) for its promotion (starting with this) and its subsequent success and widespread availability from other sources.
Surprise! It now looks like a bad bet. Benfotiamine's speculative ability to lower AGE in normal, healthy people cannot outweigh the (also still-unproven) risk that it may promote the growth and survival of nascent cancers.
Yes, I've also seen this:
Interestingly, at very high overdoses of thiamine, approximately 2500 times the RDA, thiamine supplementation had the opposite effect and caused 10% inhibition of tumour growth.(1)
So, are you going to gamble on the notion, based on this one study, performed in one particular cancer model, that you're safe if you just take even more of the stuff? My friend, please think twice. You are sowing the wind, and I fear the whirlwind to come.
And remember: there is orders of magnitude more evidence for the safety of this molecule in humans than for any other hot dietary supplement you care to mention, with (again) the exception of essential nutrients taken at doses tailored to the correction of frank deficiency. Show me, most notably, the long-term safety record for taking various phytochemicals at doses multiple times more than is present in a normal, healthy diet, such as resveratrol at more than the ~5 mg you'd get from a few glasses of red wine, or more than a hundred or so milligrams of curcumin.
Remember the concerns about a potential cancer-promoting effect of folic acid, and further worries about supra-RDA intake of selenium. Look at the metabolic mess created by just a little too much zinc. Remember the results of the trials with alpha-tocopherol for heart disease ... or antioxidants for cancer ... or the epidemiology on high-potency multivitamin use and prostate cancer ... or preformed vitamin A (retinol -- not carotenoids) and fracture risk ...Hell, even supra-RDA vitamin D supplementation is only strictly speaking evidence-based practice in osteoporotic menopausal women -- though I want to be clear that I still practice and preach this last. I'm just putting it out on the table for the plain fact that it is.*
The days of "supplements are harmless; it can't hurt, and it might help" are over, people.
-Michael
*"So what the hell do you think is sound supplementation practice, Michael??" For some ideas, see here.
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2 Population thiamine status and varying cancer rates between western, Asian and African countries.
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Thomas AA, Le Huerou Y, De Meese J, Gunawardana I, Kaplan T, Romoff TT, Gonzales SS, Condroski K, Boyd SA, Ballard J, Bernat B, DeWolf W, Han M, Lee P, Lemieux C, Pedersen R, Pheneger J, Poch G, Smith D, Sullivan F, Weiler S, Wright SK, Lin J, Brandhuber B, Vigers G.
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14 Prodrug thiamine analogs as inhibitors of the enzyme transketolase.
Le Huerou Y, Gunawardana I, Thomas AA, Boyd SA, de Meese J, Dewolf W, Gonzales SS, Han M, Hayter L, Kaplan T, Lemieux C, Lee P, Pheneger J, Poch G, Romoff TT, Sullivan F, Weiler S, Wright SK, Lin J.
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15 Overexpression of transketolase TKTL1 is associated with shorter survival in laryngeal squamous cell carcinomas.
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16 Transketolase protein TKTL1 overexpression: A potential biomarker and therapeutic target in breast cancer.
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18 Expression of transketolase TKTL1 predicts colon and urothelial cancer patient survival: Warburg effect reinterpreted.
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19 In situ localization of transketolase activity in epithelial cells of different rat tissues and subcellularly in liver parenchymal cells.
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20 Identification of novel small-molecule inhibitors for human transketolase by high-throughput screening with fluorescent intensity (FLINT) assay.
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21 Role of thiamin (vitamin B-1) and transketolase in tumor cell proliferation.
Cascante M, Centelles JJ, Veech RL, Lee WN, Boros LG.
Nutr Cancer. 2000;36(2):150-4. Review.
PMID: 10890024 [PubMed - indexed for MEDLINE]
22 [Glucose-6-phosphate dehydrogenase and transketolase activity in the blood of neurological oncologic patients preoperatively and in the dynamics of the postoperative period]
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23 [Activities of dehydrogenases of the pentose phosphate pathway and transketolase in transplanted mouse hepatomas with different growth rates and in organs of tumor carriers]
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24 Behavior of transaldolase (EC 2.2.1.2) and transketolase (EC 2.2.1.1) Activities in normal, neoplastic, differentiating, and regenerating liver.
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