Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

Vitamin C Power

Vitamin C has a benefit that may surprise you. This episode features audio from Do Vitamin C Supplements Help with Anxiety?, What Is the Optimal Vitamin C Intake?, and The Role of Vitamin C in the Treatment of Terminal Cancer. Visit the video pages for all sources and doctor’s notes related to this podcast.


Let’s say you really need to find reliable information about the best diet – for high blood pressure – or heart disease – or diabetes. Where do you go? Do you go to a website sponsored by Big Pharma that wants to sell you pills to fix your problem?

Or, do you want to treat the cause? 

Welcome to the NutritionFacts podcast – with the latest peer-reviewed research on the best ways to eat healthy – and live longer.

Today – we take a close look at the mighty power , of vitamin C. 

And, we start with the risks and benefits of using vitamin C for depression and anxiety.

“Emerging evidence suggests that higher daily intake of fiber-rich fruits and vegetables is associated with lower incidences of anxiety in adults and at the same time, greater happiness, higher life satisfaction, and greater emotional well-being.” So, “persuading people to consume more fruits and vegetables may not only benefit their physical health in the long-run, but also their mental well-being in the short-run.” Fruit consumption, for example, has protective association with leading killers like heart disease, stroke, diabetes, and cancer, as well as depression. The question is: why?

Several different mechanisms have been proposed. For example, it may be the antioxidants and anti-inflammatory properties of produce scavenging the free radicals that are involved in some of the inflammation associated with depression. If that’s the case, what about just taking vitamin C supplements? The brain has some of the highest levels of vitamin C in the body; so, the thought is if we take extra vitamin C, it may have some sort of therapeutic role in brain diseases, especially given that it’s not just an antioxidant, but also has other critical functions in the brain, such as helping to build neurotransmitters like dopamine. But you don’t know whether it actually helps, until you put it to the test.

One study found a beneficial effect of adding vitamin C as an adjunct treatment to an antidepressant, while another study found no benefit from vitamin C supplementation.

So, there are mixed results for vitamin C and depression. Here’s another study that found no benefit when it came to depression, but those randomized to vitamin C instead of placebo pills did show a significant decrease in anxiety level. And this wasn’t only seen in this study.

The effects of oral vitamin C supplementation on anxiety in students: a double-blind, randomized, placebo-controlled trial. High school students were given 500mg a day or placebo. Taking 500mg of vitamin C is about what you’d find in five oranges, four yellow kiwifruit or guavas, or one and a half yellow bell peppers. Within just two weeks, the vitamin C reduced anxiety compared to placebo, along with providing a significant drop in heart rate.

Given these data showing vitamin C may have an anxiety-reducing effect, researchers sought to find out if only a single dose could acutely affect emotional states. And indeed, within only two hours of taking some vitamin C, subjects experienced a significant drop in anxiety compared to placebo, though only among those who started out the most anxious in the first place.

As a bonus, vitamin C supplementation may lower your blood pressure a few points, but whole fruits and vegetables can do the same thing, and may even do it better for those who need it the most. As I’ve shown previously, even just adding two servings of fruits and vegetables a day can have psychological well-being benefits within only two weeks. And you won’t be put at risk of kidney stones like you would with vitamin C supplements––though that appears to be only a problem in men.

Here’s a fun fact. There are now experiments that show us how much vitamin C our body absorbs and excretes. Here’s the story.

For many years, the RDA (the recommended daily allowance) for vitamins was just based on preventing deficiency with a margin of safety. But, the minuscule amount of vitamin C, for example, needed to avoid scurvy is not necessarily the ideal intake for optimal health. So, what might be the optimal intake of vitamin C? Let’s ask the body. How might we do that? By seeing how much the body absorbs and excretes.

If you swallow 15 milligrams of vitamin C, which is what you would get eating about one-quarter of an orange, your body sucks up nearly 90 percent of it. But, if you take a supplement containing 1,250 milligrams, your body seems to realize that’s too much—and so, clamps down on absorption at the intestinal lining level, and you end up absorbing less than half.

So, by doing experiments where you slowly ratchet up the level of intake, you can see when the body starts to say, “Okay, that’s enough.”  And, that magic level of intake appears to be about 200 milligrams a day. When you take up to 200 a day, your body sucks it all up. But, above that, the body tries to block further absorption—suggesting our intestinal vitamin C transport mechanisms “have evolved to fully absorb up to about 200 mg of vitamin C” a day.

In addition, vitamin C is reabsorbed in our kidneys, back into our bloodstream, to maintain our vitamin C blood levels up at around 70 or 80 micromoles per liter. That’s the shaded region here, which is what you reach at a vitamin C intake of about 200 milligrams a day. So, even if you take ten times as much in vitamin C supplements—2,000 milligrams a day—your body will just pee and poop it out to keep your blood levels in that narrow range. So, based on these kinds of data, one might propose that 200 milligrams is the optimal daily intake of vitamin C.

You can confirm using disease data. At what daily intake of vitamin C is there the lowest stroke risk? Apparently, at about 200 milligrams a day. While dietary vitamin C intake was associated with lower stroke risk, vitamin C supplements were not—which is consistent with the overall body of evidence showing that antioxidant supplements in general don’t seem to protect against heart attacks or strokes.

But, wait, can you get up to an intake of 200 milligrams a day without taking supplements? No problem. Single servings of fruits and vegetables may have about 50 milligrams each; so, a measly five servings of fruits and veggies a day could get you to ideal blood levels.

Finally, today – what can we conclude about the role of IV vitamin C after 33 years of trials involving more than 1,500 patients?

Studies in the 70’s showed an extraordinary survival gain in terminal cancer patients with vitamin C, a simple, relatively nontoxic therapy. So, no wonder it got a lot of attention, especially when reported by a world-renowned scientist, Linus Pauling.  But studies like this in the 1980’s found no such benefit.  So, alas, they were left with the inevitable conclusion that the apparent positive results in the original study were the product of bias rather than treatment effectiveness. In the 1990’s, though, an alternative explanation arose. The disappointing 80’s research only used oral vitamin C, whereas the apparently successful 70’s experiments also gave vitamin C intravenously, and we didn’t realize until the 90’s that the same dose given IV can lead to dramatically higher levels in the bloodstream than if taken orally. So, maybe high dose vitamin C does help in terminal cancer, but maybe only when given intravenously.

Encouraging case reports continued to be published. Here, there was a regression, remission, and cure documented in individual cases of advanced kidney cancer, bladder cancer, and lymphoma. But that was three success stories out of how many? If it was three out of a hundred, or even three out of a thousand, well ok, if the treatment is sufficiently nontoxic. But there’s evidence that IV vitamin C is widely used in the alternative medicine world, as in 86 percent of  practitioners surveyed. Just those 172 practitioners alone treated about 10,000 patients a year. And you ask the manufacturers, and they’re selling hundreds of thousands of vials of this stuff in the U.S. Now, it’s not all being used for cancer, but presumably at least thousands of cancer patients are being treated every year with IV vitamin C, making the publication of three remarkable case reports seem less impressive. So, no matter how amazing these cases seemed, it’s possible the cancers just spontaneously regressed all on their own, and it was just a coincidence that it happened after they were given vitamin C. To know for sure, you have to put it to the test.

To date, there have been some small pilot studies, and the results so far have been disappointing. The good news is that even insane doses of IV vitamin C seem remarkably safe, but failed, in this study of two dozen patients, to demonstrate anticancer activity. Similar small studies have been published, all the way through to the present with tantalizing but inconclusive results.  What we do know is that the present state of cancer treatment is unsatisfactory. People have this perception that chemotherapy will significantly enhance their chances for a cure, but put all our cancer-killing chemo together and the overall contribution to 5-year survival is on the order of 2 percent. All those side-effects for 2.1 percent, at a cost of maybe $100,000 per patient per year. So, it may be worth looking deeper into therapies likes IV vitamin C. However, the lack of financial reward, since vitamin C can’t be patented and sold for $100,000, and bias against alternative medicine could dissuade conventional investigators and funding agencies from seriously considering this approach.

So, decades later what can we conclude? After trials which have included at least 1,600 patients over 33 years, we have to conclude that we still do not know whether vitamin C has any clinically significant anti-tumor activity. Although there is currently no definitive evidence of benefit, the Mayo Clinic randomized controlled trials do not negate the potential benefit based on what we now know about oral versus IV routes of administration. So, we’re kind of back to square one: does it work or not? There are highly polarized views on both sides, but everyone’s working off the same incomplete data. What we need are carefully controlled clinical trials. The question, though, is what do we do until then?

If it was completely nontoxic, then one could argue what have you got to lose, but it’s not; it’s only relatively nontoxic. For example, there have been rare but serious cases of kidney injury reported. After all, if it’s so safe, why did our bodies evolve to so tightly control against excess absorption? It can also be expensive and time-consuming. Each infusion can cost one to two hundred dollars out of pocket, since insurance doesn’t pay for it, which can be quite a boon for alternative medicine practitioners. About 90 percent of the millions of doses of vitamin C being dispensed are in for-profit arrangements; so, there’s financial pressures pushing in both directions, for and against this treatment.

Given the relative safety and expense, though, if controlled studies even find a small benefit, it would be worthwhile. And if they don’t, the vitamin C question can be put to rest once and for all, but in cancer treatment, we don’t have the luxury of jettisoning possibly effective relatively nontoxic treatments. We should revisit promising avenues, without prejudice, and with open minds.

We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition. Go to nutritionfacts.org slash testimonials. We may share it on our social media to help inspire others.

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

For a timely text on the pathogens that cause pandemics – you can order the E-book, audio book, or the hard copy of my last book “How to Survive a Pandemic.”

For recipes, check out my second-to-last book, my “How Not to Diet Cookbook.” It’s beautifully designed, with more than 100 recipes for delicious and nutritious meals. And, all the proceeds I receive from the sales of all my books go to charity.

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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.

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