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While browsing Health.SE, I came across an answer that makes the following claim:

A 2007 study by Nottingham University2 found that spicy foods can help kill cancer cells. Capsaicin, which is what makes many foods spicy, attacks the mitochondria of the cancer cells, triggering their death.

This footnote links to this BBC article, which claims that

They found capsaicin, an ingredient of jalapeno peppers, triggers cancer cell death by attacking mitochondria - the cells' energy-generating boiler rooms.

This news article does not provide their sources except for a '2007 study by Nottingham University'. I was unable to find anything about this study using Google. I also tried searching through Google Scholar and did not find anything about this.

So, I'm skeptical. If this was really discovered in 2007, why haven't I heard of it being used at all? Why can't I find the study?

Do hot peppers kill cancer cells?

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    For capsaicins to kill cancer cells but not normal cells in the body (rather than in a test tube), they would have to pass into the bloodstream unaltered by digestion and reach the cells. Is there evidence that this happens? Then there would have to be some difference in the mitochondria of cancer cells which would cause them to be selectively attacked. AFAIK there generally isn't, as mitochondria contain their own DNA. – jamesqf Jun 11 '17 at 17:26
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    Capsaicin is the chemical that causes the burning feeling. If you've ever eaten something very spicy, you'll find it burns both on the way in and the way out. So yeah, capsaicin probably isn't absorbed into your bloodstream very effectively through digestion. – DCON Jun 12 '17 at 15:54
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    @DonnachaConnolly I can vouch that accidentally eating a(n) habenero that was in the hot sauce "because you thought it was a tomato" is a very effective way to map out your digestive tract over the next few hours – Michael Jun 12 '17 at 21:38
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    Please, people, stop posting the XKCD cartoon! – Jamiec Jun 13 '17 at 11:18
  • Well, the existing link is obfuscated and the cartoon is on-topic, so people post it when they don't see it... – Vladimir F Jun 13 '17 at 11:31
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To the best of my knowledge, the paper cited by the BBC is "Vanilloid receptor agonists and antagonists are mitochondrial inhibitors: how vanilloids cause non-vanilloid receptor mediated cell death" (PMID: 17214968 DOI: 10.1016/j.bbrc.2006.12.179), which lists Timothy E Bates as an author (the last one, which means he was the primary investigator -- h/t Mad Scientist for correcting my mistake on that), coming from the University of Nottingham School of Biomedical Sciences, and published "2007 Mar 2" (online 2007 Jan 2). The abstract says

These data support the hypothesis that (E)-capsaicin [...] are all mitochondrial inhibitors, able to activate apoptosis and/or necrosis via non-receptor mediated mechanisms, and also support the use of TRPV1 ligands as anti-cancer agents.

As to why this isn't widely used (yet?), that BBC article you linked to says

However, Josephine Querido, cancer information officer at Cancer Research UK, said: "This research does not suggest that eating vast quantities of chilli pepper will help prevent or treat cancer.

"The experiments showed that pepper extracts killed cancer cells grown in the laboratory, but these have not yet been tested to see if they are safe and effective in humans."

Cancer Research UK recommends reducing the risk of cancer by eating a healthy, balanced diet, with plenty of vegetables and fruit.

And, of course, things that kill cancer cells in a petri dish aren't necessarily useful as cures.

I searched Google quickly for "capsaicin cancer," and found some more recent articles about it, including "Anticancer Properties of Capsaicin Against Human Cancer" (PMID: 26976969), from March 2016. (The article is freely available online, on the Anticancer Research website.) The abstract of that review article mentions a few different ways that capsaicin might affect cancer, not just as mitochondrial inhibitors. However, they also write that more study is needed before capsaicin can be utilized practically to fight cancer:

While the preponderance of the data strongly indicates significant anticancer benefits of capsaicin, more information to highlight molecular mechanisms of its action is required to improve our knowledge to be able to propose a potential therapeutic strategy for use of capsaicin against cancer.

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    "things that kill cancer cells in a petri dish aren't necessarily useful as cures" - To add to this, barring an explanation for why/how capsaicin can trigger apoptosis only in cancerous cells, the default hypothesis would generally be that ingesting sufficient amounts of capsaicin to kill cancer cells may be quite damaging to your normal, healthy cells as well. – aroth Jun 12 '17 at 6:37
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    Mitochondria are present and indispensable in most human cell types. As @aroth writes, something that non-specifically inhibits mitochondrial function may be about as useful against cancer as hard radiation - which does kill cancer cells, yes, but also healthy cells, and so must be carefully targeted. – S. Kolassa - Reinstate Monica Jun 12 '17 at 10:31
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    @StephanKolassa Wouldn't Chemotherapy be a more relevant treatment for comparison? – JimmyJames Jun 12 '17 at 14:49
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    The hard part of curing cancer isn't killing cancer cells. The hard part is not killing the patient as a side effect. – Mark Jun 13 '17 at 0:37
  • @Mark just curious, are you quoting someone, or is that an original? – SQB Jun 18 '17 at 15:35

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