Naked Science Forum
On the Lighter Side => Complementary Medicine => Topic started by: Andrew K Fletcher on 14/06/2009 10:45:27
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Vitamin C 'slows cancer growth'
TREATMENT IMPACT
See the impact of vitamin C treatment on mice with tumours.
An injection of a high dose of vitamin C may be able to hold back the advance of cancers, US scientists claim.
The vitamin may start a destructive chain reaction within the cancer cell, they add.
The jab halved the size of brain, ovarian and pancreatic tumours in mice, reported the journal Proceedings of the National Academy of Sciences.
However, Cancer Research UK said other studies suggested large vitamin C doses may interfere with cancer treatment.
This is encouraging work but it's at a very early stage because it involves cells grown in the lab and mice
Dr Alison Ross
Cancer Research UK
Earlier research by the team at the National Institutes of Health in Maryland had suggested that the vitamin, also called ascorbate, could kill cancer cells in the laboratory.
After these successful tests in mice, they are now suggesting that the treatment be considered for human use at similar levels.
The dose they employed - up to four grams per kilo of bodyweight - was far greater than any that could be achieved using diet or vitamin pills, as the digestive system does not absorb more than a fixed amount taken orally.
The mice were bred to have malfunctioning immune systems, then injected with human cancer cells, which as a result, grew quickly into large tumours. The vitamin was then injected into their abdominal cavity.
Tumour growth and weight fell by between 41% and 53%, and while in untreated mice, the disease spread rapidly to involve other body parts, no such spread was seen in the vitamin C-treated animals.
The researchers wrote: "These pre-clinical data provide the first firm basis for advancing pharmacologic ascorbate in cancer treatment in humans."
Peroxide bomb
The treatment works because a tumour cell is chemically different to a healthy cell.
The vitamin C reacts with this chemical make-up, producing enough hydrogen peroxide to kill the cell, while leaving healthy cells unscathed.
However, Dr Alison Ross, from Cancer Research UK said that much more work would have to be done to see if vitamin C could be a viable treatment.
"This is encouraging work but it's at a very early stage because it involves cells grown in the lab and mice.
"There is currently no evidence from clinical trials in humans that injecting or consuming vitamin C is an effective way to treat cancer.
"Some research even suggests that high doses of antioxidants can make cancer treatment less effective, reducing the benefits of radiotherapy and chemotherapy."
Images of mice showing tumours trated with ascorbate and controls.
http://news.bbc.co.uk/nol/shared/spl/hi/pop_ups/08/health_enl_1217848958/img/1.jpg
http://news.bbc.co.uk/1/hi/health/7540822.stm
Vitamin C 'helps to fight cancer'
oranges
High dose vitamin C injected into the bloodstream help fight cancer
High doses of vitamin C injected into the bloodstream may help fight cancer, a US study says.
Scientists found that intravenous vitamin C in the form of ascorbate killed cancer cells in lab tests.
The findings contradict earlier studies, but the Maryland-based Institutes of Health said they had looked at lower-dose oral vitamin C.
Cancer experts said the "overwhelming" evidence still suggested vitamin C was not an effective treatment.
Studies in the 1970s first suggested the administration of high doses of vitamin C could help treat cancer, but later research did not back this up.
There are many substances that have been shown to kill cancer cells in the lab but failed to fulfil that promise when tested in people
Henry Scowcroft, of Cancer Research UK
In the latest study, published in the Proceedings of the National Academy of Sciences, researchers conducted laboratory experiments which simulated clinical infusions of vitamin C on a range of nine cancer and four normal cells.
In five of the cancer lines, there was a 50% decrease in cell survival, while normal cells were unaffected.
A more detailed look at lymphoma cells - which were especially sensitive to ascorbate - showed they were killed completely.
The effective dose was around four millimoles, a concentration much higher than an oral dose but easily achievable by intravenous infusion.
Cells
Researchers were unable to explain what caused the results, although they did note the treatment led to the formation of hydrogen peroxide, a chemical known to be toxic to cells.
Alternative medicine practitioners have already administered high doses of intravenous ascorbate.
INTRAVENOUS VITAMIN C and CANCER
by Ron Hunninghake, M.D.
"...it takes much more than logic and clear-cut demonstrations to overcome the inertia and dogma of established thought." — Irving Stone
Irving Stone was an early thinker and writer about vitamin C (its scientific name is ascorbic acid). He knew it would be an uphill battle to change the way the medical profession viewed vitamin C. While most doctors accept that scurvy is a vitamin C deficiency illness, few have made the rather humongous jump to seeing high dose intravenous vitamin C as a major player in the management of cancer.
Lead researcher Dr Mark Levine said the treatment would have to be proved safe before being given to patients.
But he added: "Ascorbate as a potential cancer therapeutic agent has a controversial and emotionally charged past."
Henry Scowcroft, senior information officer at Cancer Research UK, said despite the findings, the "overwhelming" evidence still pointed to vitamin C not being an effective treatment.
"This work is at a very early stage. There are many substances that have been shown to kill cancer cells in the lab, but failed to fulfil that promise when tested in people.
"But we do know that eating a healthy, balanced diet, including plenty of fresh fruit and vegetables, is an effective way to reduce the risk of getting cancer in the first place."
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OK, Lets have a close look at all that.
"Cancer Research UK said other studies suggested large vitamin C doses may interfere with cancer treatment."
"This is encouraging work but it's at a very early stage because it involves cells grown in the lab and mice."
"The mice were bred to have malfunctioning immune systems, "
"There is currently no evidence from clinical trials in humans that injecting or consuming vitamin C is an effective way to treat cancer.
Cancer experts said the "overwhelming" evidence still suggested vitamin C was not an effective treatment.
"Studies in the 1970s first suggested the administration of high doses of vitamin C could help treat cancer, but later research did not back this up."
"Some research even suggests that high doses of antioxidants can make cancer treatment less effective, reducing the benefits of radiotherapy and chemotherapy."
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Ok let's have a closer look.
Read a while back a little about those "other studies" turned out they used a much lower oral dose, compared to the very high doses used intravenously.
BRIEF COMMUNICATION
Vitamin C Pharmacokinetics: Implications for Oral and Intravenous Use
right arrow Sebastian J. Padayatty, MRCP, PhD; He Sun, PhD, CBS; Yaohui Wang, MD; Hugh D. Riordan, MD; Stephen M. Hewitt, MD, PhD; Arie Katz, MD; Robert A. Wesley, PhD; and Mark Levine, MD
6 April 2004 | Volume 140 Issue 7 | Pages 533-537
Background: Vitamin C at high concentrations is toxic to cancer cells in vitro. Early clinical studies of vitamin C in patients with terminal cancer suggested clinical benefit, but 2 double-blind, placebo-controlled trials showed none. However, these studies used different routes of administration.
Objective: To determine whether plasma vitamin C concentrations vary substantially with the route of administration.
Design: Dose concentration studies and pharmacokinetic modeling.
Setting: Academic medical center.
Participants: 17 healthy hospitalized volunteers.
Measurements: Vitamin C plasma and urine concentrations were measured after administration of oral and intravenous doses at a dose range of 0.015 to 1.25 g, and plasma concentrations were calculated for a dose range of 1 to 100 g.
Results: Peak plasma vitamin C concentrations were higher after administration of intravenous doses than after administration of oral doses (P < 0.001), and the difference increased according to dose. Vitamin C at a dose of 1.25 g administered orally produced mean (±sd) peak plasma concentrations of 134.8 ± 20.6 µmol/L compared with 885 ± 201.2 µmol/L for intravenous administration. For the maximum tolerated oral dose of 3 g every 4 hours, pharmacokinetic modeling predicted peak plasma vitamin C concentrations of 220 µmol/L and 13 400 µmol/L for a 50-g intravenous dose. Peak predicted urine concentrations of vitamin C from intravenous administration were 140-fold higher than those from maximum oral doses.
Limitations: Patient data are not available to confirm pharmacokinetic modeling at high doses and in patients with cancer.
Conclusions: Oral vitamin C produces plasma concentrations that are tightly controlled. Only intravenous administration of vitamin C produces high plasma and urine concentrations that might have antitumor activity. Because efficacy of vitamin C treatment cannot be judged from clinical trials that use only oral dosing, the role of vitamin C in cancer treatment should be reevaluated.
Sebastian J. Padayatty, Hugh D. Riordan, Stephen M. Hewitt, Arie Katz, L. John Hoffer, Mark Levine
Intravenously administered vitamin C as cancer therapy:
three cases http://www.cmaj.ca/cgi/reprint/174/7/937
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A study of healthy volunteers doesn't really tell you a lot about the effect of vitamin C on cancer. It would be interesting to see what adverse effects (if any) were observed in people dosed with about 0.1% of their body weight.
The fact that you can pour more acid into someone's bloodstraem that you can get to travel through the gut wall isn't that shocking.
Why do you think that a lot of drugs are given by injection?
Contrary to popular belief, it's not because doctors like sticking needles in patients. (they do, but that's just a side benefit).
It's reasonable enough to say that "the role of vitamin C in cancer treatment should be reevaluated.", but only if there is some other evidence for a carcinolytic effect of vitamin C or a theoretical reason why it should have such an effect.
3 cases of aparent remission is interesting. It's certainly grounds for further testing, particularly since the stuff is dirt cheap and not very toxic.
However, 3 cases isn't a proven cure.
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BC I agree with you that 3 cases is not enough to prove it either way and there will be more cases out there that have worked and probably even more that have not worked, but it should be investigated further, and as you say it is not an expensive drug, but this is the point of the forum to open up subjects for debate and investigate possibilities rather than accepting the impossibilities associated with cancer and many other illnesses with the poorest of prognosis.
The pictures of the mice were interesting did you follow the link?
Andrew
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Just incase anyone comes here by google and doesn't already know:
1) there's very little evidence of any benefit for cancer in taking large doses of vitamin C orally
2) for people on chemotherapy there is some evidence that vitamin C is measurably counter-productive, as it protects the cancer cells against the chemo agents
http://www.reuters.com/article/scienceNews/idUSTRE49010120081001
so don't start supplements without talking to your treating doctor (I haven't got time to look for better coverage than the Reuters release, so I haven't read it properly either)
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Hi Rosy
For anyone coming here by google:
1. Chemotherapy has been the main treatment for most cancers.
2. Deaths from cancer continue to increase
3. Studies conducted to test vitamin C have deliberately used low doses so will inevitably produce the desired negative results!
4. blunted results from chemotherapy study translated could mean also had a curative / protection effect for the cells in the body!
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I think Rosy was just being responsible - in case anyone decides to try self-medicating with high dose vit c without discussing it with their doctor first.
but...
3. Studies conducted to test vitamin C have deliberately used low doses so will inevitably produce the desired negative results!
Tests have used lower dosages, yes, but nowhere does it say that this was to intentionally produce negative results - this is your irrational bias showing through.
4. blunted results from chemotherapy study translated could mean also had a curative / protection effect for the cells in the body!
Are you aware of what cancer cells are?
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A study of healthy volunteers doesn't really tell you a lot about the effect of vitamin C on cancer. It would be interesting to see what adverse effects (if any) were observed in people dosed with about 0.1% of their body weight.
not a whole lot, its LD50 is 11.3g per kg of body weight. thats a lot!
apparently many animals can produce it themselves...
it can cause iron poisoning in people with high iron (as it helps the body to absorb iron)
might have a link to kidney stones
high megadoses during early pregnancy (in rats) can suppress progesterone production, and cause miscarriage
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3 cases of apparent remission is interesting. It's certainly grounds for further testing, particularly since the stuff is dirt cheap and not very toxic.
However, 3 cases isn't a proven cure.
I knew it this way:
1 case is just 1 case.
2 cases are a coincidence.
3 cases are worth a scientific paper...
...still far away from any proof or evidence! [;)]
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A study of healthy volunteers doesn't really tell you a lot about the effect of vitamin C on cancer. It would be interesting to see what adverse effects (if any) were observed in people dosed with about 0.1% of their body weight.
not a whole lot, its LD50 is 11.3g per kg of body weight. thats a lot!
apparently many animals can produce it themselves...
it can cause iron poisoning in people with high iron (as it helps the body to absorb iron)
might have a link to kidney stones
high megadoses during early pregnancy (in rats) can suppress progesterone production, and cause miscarriage
At roughly a tenth of the LD50 I would expect some symptoms.
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It is a complementary / alternative forum.
Yes I do understand what cancer cells are. Dad, wifes mum, grandmother, died of this dreadful condition and many friends have over the years. Don't need a lecture on what it is and what it does thanks Ben.
We need to go in a completely different direction if we are ever to treat this condition and prevent deaths. Bombarding the body with highly toxic chemicals in the hope that you get all the cancer cells is unlikely and the damage it does to the normal cells in the body is a high price to pay for a hit and miss approach.
However, a new approach using chemo therapy in Germany is introducing the toxic soup directly into the tumours causing a far less toxic localised treatment that is showing much promise. Again early days but certainly a lot less hit and miss.
I think Rosy was just being responsible - in case anyone decides to try self-medicating with high dose vit c without discussing it with their doctor first.
but...
3. Studies conducted to test vitamin C have deliberately used low doses so will inevitably produce the desired negative results!
Tests have used lower dosages, yes, but nowhere does it say that this was to intentionally produce negative results - this is your irrational bias showing through.
4. blunted results from chemotherapy study translated could mean also had a curative / protection effect for the cells in the body!
Are you aware of what cancer cells are?
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i worked in a hospital and knew many people who died after they started chemo. In fact, I don't know one survivor who had cancer that spread, went on chemo and lived. I'd say you'd have a better shot at avoiding sugar and going on an adam and eve diet.
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It is a complementary / alternative forum.
My personal feelings about this section of TNS aside.. complimentary means in conjunction with, I'm assuming, modern medicine.. not complete disregard of.
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Conventional chemotherapy is nasy by all accounts. It uses drugs that simply would not be used for any other condition. That's why it's pretty much only used for people who are terminally ill. That's why most people die after chemo- the point being that they die later than they otherwise would have.
Of course there are some orther less agressive forms of pharmacological therapy that are not in this category; like tamoxifen where it's amot point if it should be considered chemotherapy.
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Chemtester, Thanks for your post, it tells it just the way it is. The question is why do we keep going down the same old tried & tested & lethal route when so many £billions have been invested in finding a different path? The answer is of course do the people who stand to gain the most money really want to shoot themselves in the foot and eliminate such a lucrative income by finding either a cause or a cure?
Why not invest a fraction of that money into finding an alternative treatment?
More to the point why not invest that money into finding the cause?
http://www.mymeso.org/tags/johann-wolfgang-goethe-university-of-frankfurt/ One such pioneer who has produced some impressive results by applying common sense to chemotherapy and should having more attention to his research has recently recieved some mainstream publicity.
i worked in a hospital and knew many people who died after they started chemo. In fact, I don't know one survivor who had cancer that spread, went on chemo and lived. I'd say you'd have a better shot at avoiding sugar and going on an adam and eve diet.
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There has been much debate over ascorbate ever since the 1970s when Linus Pauling published research showing significant positive effects of large intravenous (IV) doses. It's a very heated issue, with those opposing relying on:
1. studies based on oral administration of vitamin C, which does not allow blood concentration to reach therapeutic levels
2. the fact that many mainstream cancer treatments rely on reactive oxygen species (the very species antioxidants quelch) to destroy tumours via chemotherapy and vitamin C, as a known antioxidant, could potentially interfere with chemotherapy.
The recent research suggests that, in high IV doses, ascorbate ceases to act as a antioxidant and instead delivers hydrogen peroxide selectively to cancer cells, triggering tumor cell death.
IV vitamin C used as a cancer treatment would constitute a very disruptive technology, with most oncologists lacking the training to create and deliver the requisite protocols, even though such protocols exist (I've experienced them myself and seen firsthand the unnnecessary fear among doctors and nurses associated with delivering IV ascorbate). The disruptiveness would also extend to the economic sphere, as vitamin C is much, much cheaper than chemotherapy and the pharmaceutical industry would have every incentive to resist its introduction.
This debate will continue for years, but it's time some serious large scale clinical trials took place.
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Iconoclast. I agree it is time for clinical trials with this simple yet logical approach and as some politicians and even the directors of the drug companies will eventually inevitably have to face cancer maybe it's time they stopped playing at research and got their heads around their own mortality for once.
Andrew
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I always wonder who these " politicians and even the directors of the drug companies " are.
They must be a bunch of politicians who don't want to save the taxpayer money- which is odd and directors of companies who are not only utterly amoral, but who, as you say, even on their deathbeds don't have the sense to say "OK, It's a fair cop- we lied about the cancer drugs. Get me some vitamin C!".
It seems they are prepared die to protect a secret that won't help themselves or their loved ones
Do you understand why I don't believe in them?
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People become blinkered when £$ signs hang in front of their eyes and tend to want to make more and more money as proven with some of the horror drug stories that have unfolded even on this forum.
Ironically it is this blinkered approach to everything that will eventually bring about their own demise.
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I think there's a difference between "blinkered" and "suicidal".
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The Naked Scientists do not endorse any of Andrew K Fletcher's Physical, Biological or Medical assertions or opinions, regardless of any impression he may give on his own website.
Why would they? Who asked them to? The impression I may give?
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The question is why do we keep going down the same old tried & tested & lethal route when so many £billions have been invested in finding a different path? The answer is of course do the people who stand to gain the most money really want to shoot themselves in the foot and eliminate such a lucrative income by finding either a cause or a cure?
In january 2010, I'll start working for the EORTC (European Organization for Research and Treatment of Cancer). This is a non-profit organization, just like the NCI (National Cancer Institute) in the USA... How do you reconcile your quoted opinion with the existence of such npo's?
And Andrew, I sincerely hope you'll never get cancer, but if you would get it, would you ignore your physician's medical advice and self-medicate with huge doses of prescription-free Vitamin C?
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Who knows, I will let you know. But I would not have chemo therapy mega dose either. Mustard gas is not that appealing to me having watched what it did in the trenches.
However, in Frankfurt a doctor is catheterizing tiny amounts of cheomtherapy directly into the tumor. Now this appears logical rather than poisoning the whole body and inducing multiple organ failure.
This is a discussion forum, let us not conveniently forget this. My post in the "alternatives forum was to stimulate some interesting debate, not to stimulate some rather blinkered attacks.
I like the idea that alternatives such as ascorbic acid is being investigated by universities around the globe.
I do not like the rip off merchants mentioned by BC charging extortionate amounts of money for what is after all a very inexpensive vitamin.
Yet, Chemo therapy is another inexpensive group of chemicals, why is so much money made from it?
And what are the real costs to the people who receive it and their after care?
Frequency and Cost of Chemotherapy-Related Serious Adverse Effects in a Population Sample of Women With Breast Cancer
http://jnci.oxfordjournals.org/cgi/content/short/98/16/1108
Chemotherapy recipients incurred large incremental expenditures for chemotherapy-related serious adverse effects ($1271 per person per year) and ambulatory encounters ($17 617 per person per year). Conclusions: Chemotherapy-related serious adverse effects among younger, commercially insured women with breast cancer may be more common than reported by large clinical trials and lead to more patient suffering and health care expenditures than previously estimated.
Michael J. Hassett, A. James O'Malley, Juliana R. Pakes, Joseph P. Newhouse, Craig C. Earle
I do not have to reconcile my opinion just follow the money.
Andrew
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I do not have to reconcile my opinion just follow the money.
That'll be a short journey in a non-profit organization.
And for the big pharma companies: they have to recuperate their research costs. A patent on a medicine is valid for about 20 years. Pharma companies take patents on experimental drugs that show promise in the lab (in bacterial systems). After about 10 years, the experimental drugs would be ready to be sold on the market if all clinical trials prove that it's an improvement compared to current drugs on the market.
So the big pharma now has 10 years exclusiveness on the market to sell their drugs, before other pharmas can make the cheap generic version. However, the big pharma will have invested about 1 billion dollars in the research of this new drug that has to be recuperated, plus all costs for candidate experimental drugs that never reach the market (which most people tend to forget). So on average, to break even, a big pharma must earn about 100 million per year, because after 10 years, nobody will buy this medicine anymore and everyone will buy the cheaper generic medicine.
Now, if big pharma's would be forced by governments to lower their prices, the effect will be that after a few decades, there will be no more new drugs on the market, because no big pharma would take the risk to invest in experimental drugs without the guarantee that it would be approved to be distributed.
Disclaimer: the numbers I've used are realistic estimates, not exact.
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"Yet, Chemo therapy is another inexpensive group of chemicals, why is so much money made from it?
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Actually, some of them are quite expensive to make but the real costs are due to the fact that they are relatively small volume products- there isn't the ecconomy of scale you get with aspirin (or, indeed, with vitamin C).
Another factor is that they are really quite toxic chemicals so the precautions needdd in the manufacturing plant are expensive.
Don't get me wrong- I know that the drugs companies make big profits (for reasons Nizzle explained) but you still need to answer the point I made earlier about the VP of a drug company dying rather than blowing the whistle and saying "Never mind the chemotherapy- get me some vitamin C".
There's no money involved here (just the price of an orange to a rich man).
You really do need to reconcile that if you want to be taken seriously.
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Vitamin C is key to creating stem cells
Vitamin C could be used to overcome hurdles in creating stem cells for treating human diseases, scientists believe.
Published: 5:00PM GMT 24 Dec 2009
The vitamin boosts the reprogramming of adult cells to give them the properties of embryonic stem cells.
Scientists who made the discovery believe it may help them overcome long-standing problems in creating the reprogrammed cells, called induced pluripotent stem cells (iPSCs).
IPSCs offer a solution to the ethical problems involved in producing embryonic stem cells with the potential to become any kind of human tissue, from bone to brain.
Embryonic stem cells have to be extracted by cannibalising early stage embryos obtained from fertility clinics. IPSCs, on the other hand, are made in the laboratory from ordinary adult cells by altering their genes.
Many experts believe iPSCs are the future of stem cell medicine, since they behave in a similar way to embryonic stem cells and are also capable of developing into a wide range of tissues.
The conversion of ordinary cells into iPSCs is highly inefficient and difficult to achieve. Often the cells age prematurely and stop dividing or may die, a process known as senescence.
more...
http://www.telegraph.co.uk/health/he...tem-cells.html
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Interesting stuf, but not an answer to my question.
Why don't you answer?
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Which is the question you want answered?
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imho vitamin c is probably more of a preventive of getting certain types of cancer.in the olden days people believed cancer was contagious and that idea was scoffed at and/or forgotten until the last 20 years when lo and behold medical science has found correlation between certain types of cancer,genetic predispostion and viruses.Eat healthy,avoid fatty and fried foods etc is your best bet.My Dad, god bless his soul, was diagnosed with pancreatic cancer at age 74-one of the worst, most agressive cancers you can get.he lived and basically recovered from a major stroke at age 60;had heart disease and a bypass 6 months before he was diagnosed with pancreatic cancer.he had been on coumidin, a blood thinner since he had a stroke and had to avoid any vegetables and other foods with high ammounts of vitamin D. i heard recently that there was a correlation between vitamin D and pancreatic cancer and wonder if that had contributed to his getting cancer.
you can flame me, think I am an idiot whatever but in my opinion chemotherapy and radiation is a barbaric treatment-I'm not saying it is not without merit or cure some people diagnosed at early stages of cancer.I've seen the other side of it-it's not pretty. They are basically trying to kill the cancer without killing you. Mark my words -in the future it will be considered a barbaric practice much like medicine in the past.
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"imho vitamin c is probably more of a preventive of getting certain types of cancer."
Why?
Is there any actual science that shows this?
It might be true; I don't know but, since this is a science forum. just saying "I think..." won't do.
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well it makes logical sense to me. its a known fact viruses trigger cancer onset. I'm sure you wont argue a diet rich in vitamins helps prevent or reduce effects of illnesses such as cold or flu. Its also a known fact your general diet can increase your risk of cancer among other illnesses. There is a correlatioj between diets rich in certain foods,culturally speaking and the certain cancers that are prevalent in certain countries.For example china/asian countries had high rates of stomach cancer. America, I believe(by 'I believe' I mean I am not sure which cancer was prevalent in North America 20 years ago but there was one prevalent type)had higher rates of lung cancer. At least 20 years ago they were-this might have changed since the times have changed. But you get my point-the fact that diet affects your health. Don't get me wrong-I in no way believe once you get cancer that any ammount of vitamins or change in a diet will rid your body of cancer. I do in fact believe it can prevent it in alot of types of cancer, I also believe it is foolhardy to discount the idea since it is logical and harmless to take care of your body with a balanced and healthy diet.
Yes this is a science forum but it is not a scientific journal.I don't see anhywhere in the rules regarding posting scientific study data only. I don't feel the need to defend my 'opinion' since they are based on facts and logical thought. I stand by my right to post my thoughts ideas and responses as i see them. Theres no need to try to inflame me -it wont work. [;)]
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There is virtually no chance that vitamin C can be a cure for all cancers. That being said, there is the possibility that vitamin C therapies can work against certain types of cancers. How this might work depends on the cancer and the system you are testing it in. For example, vitamin C has been shown to reduce inflammation, an important part of etiology of some cancers. Vitamin C may also affect the immune system, which may also have an effect in defense against cancer. Vitamin C has recently been used intravenously to produce levels of hydrogen peroxide that may be cytotoxic to cancer cells. Vitamin C also may work with existing therapies (such as chemo) to prevent damage to normal tissues.
I could go on. There's a lot of possibilities, but that's all they are: POSSIBLE answers. Not a lot of people are researching vitamin C and cancer right now. It's not an easy thing to do.