Dr. Amy Tuteur is an obstetrician-gynecologist. She received her undergraduate degree from Harvard College and her medical degree from Boston University School of Medicine. Dr. Tuteur is a former clinical instructor at Harvard Medical School.

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APRIL 1, 2010 7:38AM

Do vitamins increase the risk of cancer?

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vitamin supplements

Among believers in alternative health, it is an article of faith that vitamin supplements prevent all manner of serious diseases including cancer. Yet the reality is almost exactly the opposite. According to Kristal and Lippman, writing in the Journal of the National Cancer Institute (Nutritional Prevention of Cancer: New Directions for an Increasingly Complex Challenge):

The prospects for cancer prevention through micronutrient supplementation have never looked worse. Several large, randomized cancer prevention trials have recently reported no reduced risk from micronutrient supplementation, and [there is] a growing body of evidence that micronutrient supplementation may be harmful...
The authors are commenting on a paper that appears in the same issue of JNCI that investigated whether folate supplementation decreased the risk of precancerous growths in the colon. Folate did not decrease the risk; it increased it by 67%. Further analysis revealed that folate supplementation increased the risk of prostate cancer by 167%.

The authors note:
... Among studies addressing micronutrient supplementation for the prevention of cancer, only a single randomized trial, testing 1200 mg of calcium for preventing the recurrence of colorectal polyps, has reported a statistically significant and positive result for its primary cancer outcome, whereas large trials testing supplementation with multivitamins, folate, selenium, β-carotene, and vitamins E, C, D, B 6 , and B 12 have found no benefits.
... Even clinical trials designed to test agents that were found to reduce cancer risk in secondary analyses of previous trials, such as vitamin E and selenium for prevention of prostate cancer, have failed to find benefit from supplementation. The harmful effects of β-carotene supplementation in heavy smokers are well established, and it now appears that folate supplementation may increase cancer risk as well...
The scientific rationale for testing vitamin supplements for cancer prevention was sound. A variety of studies have shown that people who don't have cancer have higher levels of certain micronutrients. Unfortunately, the assumption that these vitamins and minerals prevent cancer was unjustified.
... the notion that some is good and therefore more is better has been proven wrong; it is more likely that for any given micronutrient, there is an optimal range of intake.
That's not surprising, considering how vitamins and minerals function within the body. Micronutrients are like nails in a house. Without enough nails to hold the various parts together, a house will fall apart. However, once the optimal number of nails has been reached, adding more will not increase the stability of the house and in large amounts, might even decrease stability.

That explains why vitamin supplements fail to prevent cancer. How would supplements act to cause cancer?
... using the folate supplementation trial as an example, it is not unreasonable to assume that optimal levels of folate are associated with more fidelity in DNA replication and thus a lower risk of spontaneous mutations, but high folate may also support more rapid cell growth and promote carcinogenesis in previously initiated cells.
Another possibility is that large quantities of specific vitamins or minerals may be consumed by particular types of cancer. In that case, low levels of that vitamin or mineral in cancer patients reflect the fact that the cancer needs the micronutrient. The level has dropped not because high levels of the vitamin or mineral prevent cancer, but because the cancer has used up what is available. Far from preventing cancer, supplements might actually feed the cancer and promote rapid growth.

Whatever the reason, it is clear that supplements do not represent the next frontier in cancer prevention. As the authors acknowledge:
... It is safe to conclude that cancer prevention is not going to be as simple as recommending high-dose micronutrient supplements for middle-aged and older adults.

In fact, the opposite may turn out to be true. Vitamin and mineral supplements may promote cancer growth

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When I was diagnosed with cancer in 2004 I went on a vitamin kick and I found that large doses of vitamins... along with radiation treatment, worked:) Hmmm... maybe it was more the radiation treatment...

My oncologist told me in 2004 that he believed that large doses of vitamins could make cancer cells grow faster... made sense to me. Rated.
Maybe vitamins work like placebos. I have thought for a while that vitamins aren't completly healthy, I knew someone who worked in a plant that made vitamins and basically they aren't really regulated, like the doses aren't necessarily consistant pill to pill.
"My oncologist told me in 2004 that he believed that large doses of vitamins could make cancer cells grow faster"

Some forms of cancer are treated by interfering with the action of folate in the body. Taking folate reverses the effect of the chemotherapy.
"like the doses aren't necessarily consistant pill to pill."

That's true.
Amy, do you take any vitamins? Doesn't the AMA recommend vitamins now after it had previously not? It's funny you should write this now; I only just started taking vitamins. Nothing dramatic or excessive, just the simpler ones. Here's what I take every day: 1 multivitamin (not brand conscious, even though I notice that different brands have differing amounts of doses, although most are in the same ballpark); 1,000 D; 1 capsule fish oil supplement. What do you think of this regimen? I'm just curious if you take anything at all. In case you'll ask, I don't eat the best diet in the world.
everything in moderation ! I'm not surprised really. Far too often we think what works for one will work for another. Makes me feel ahead of the game refusing to take tons of vitamins that friends would try to push on me . chicken soup and a glass of OJ. more than enough.

"do you take any vitamins?"

No, I don't.

I just found out I have low vitamin D and my doctor recommend supplementation. I couldn't find much data that vitamin D supplements reduce the risk of disease, and I did see a small study that suggested that in African Americans vitamin D increased the risk of heart disease. It appears that vitamin D supplementation caused plaques in arteries to become calcified and therefore worse. I'm still trying to figure out what I am going to do.
"chicken soup and a glass of OJ. more than enough."

It's funny, but that's probably true for most people.
Your attacks on anything that might limit the medical establishment's profits continue. But doesn't matter. The American medical establishment is dying, victim of its own failures and greed. It's pricing itself out of existence and when that happens, people will find that maintaining quality health is really quite simple. Children can learn to do it.

No one needs expensive "experts" nor anything you silly, greedy AMA people offer as the public will soon find out, not to mention the fact that you kill around 500,000 people a year, more than any other cause!

And what's that latest disastrous pharmaceutical, the one for osteoporosis that actually CAUSES osteoporosis?! It causes the femur, the largest bone in the body, to snap and break! How many antidepressants actually CAUSE suicidal thoughts, even suicide?

My God! Snap out of your delusion, woman! You're part of a "con" that's killed millions of people!!
It would be kind of you to supply actual references that all of us in science are used to. Paraphrasing from a journal does not lend itself to authenticity. Research in any field does lead to conflicting results and from time to time and definitely need to be reassessed and revitalized. That is the every essence of peer-review. Knowledge does move forward and I am sure you will agree that medical advise given by celebrities or doctors is pretty serious business and needs far more scrutiny before being published as evidence based data.
You say, "I couldn't find much data that vitamin D supplements reduce the risk of disease"

I found a good number of studies have been published on PubMed regarding Vitamin D (or precursors) supplements in heart disease, osteoporosis, pregnancy and cancer. I haven't not read them all, so I would not try to summarize their findings. But considerable research exists, and appears to favor appropriate supplementation in specific conditions and populations.
I totally agree!

The best revenge is eating right, and getting your micronutrients from lots of fruits and vegetables. I dont really know how too much of most nutrients would be deleterious, as most are water soluble and are peed out quickly.

I am indecided as well regarding Vitamin D--as the majority of folks I'm checking these days seem borderline, and many are deficient. I have a friend who is an epidemiologist at the CDC, and they are having trouble establishing what is truly normal, especially for people with darker skin (who have lower vitamin D levels, but get much less osteoporosis). You would probably agree, that most of our patients just need to eat much better than they are, and exercise more!
Maybe it's a good thing that I am allergic to the binders in vitamins and unable to take them.
Vitamin D seems to be the new focus. I know the Cleveland Clinic has looked at it. All of a sudden it seems that even increasing by 1,000 or more doesn't budge the level in the blood. They say that boosting by tens of thousands to get it up and then maintaining at 1,000 is about right for some people who are low. I'm getting this from memory from an article in Cleveland here, but I've heard anecdotally that people I know/patients at the Clinic are being treated that way. Anyway, I'm curious if this will ultimately look like a fad in the rear view mirror.
Interesting article. thank you Dr Amy.
"But considerable research exists, and appears to favor appropriate supplementation in specific conditions and populations."

I'm looking for large, long term studies that give us a full appreciation for what happens when vitamin D supplementation is prescribed.
The question I want to ask is: do you recommend the pre-natal vitamins to your patients? It seems like that would be common sense, since it can help a woman be well-nourished during pregnancy and any increased risk of disease won't extend for more than a year or so.
"do you recommend the pre-natal vitamins to your patients?"

Prenatal vitamins are the standard of care and are recommended to reduce the risk of vitamin deficiencies which can have serious consequences in pregnancy. They are used only for a limited time. That's very different taking vitamin supplements for the express purpose of preventing chronic diseases like cancer and heart disease.