¿Te has preguntado si existe una manera natural de bajar tus niveles de presión arterial, protegerte contra el alzhéimer, perder peso y sentirte mejor? Resulta que sí la hay. El doctor Michael Greger (FACLM), fundador de NutritionFacts.org y autor del rotundo éxito de ventas del New York Times "How Not to Die" (Comer para no morir), nos presenta la nutrición basada en la evidencia para añadir años a nuestra vida y vida a nuestros años.

I know that the news today can be overwhelming, even just mentioning the word facts can trigger all sorts of reactions.  I’m Dr. Michael Greger and I happen to really like facts! So, I’ve devoted my life to learning all there is to know about the latest nutrition research, so that you and your family can lead healthier, more productive lives.

Today we do some detective work on vitamin supplements – by asking a few key questions; first: do we need them – and if so – what kinds do we need? 

As it turns out there are two vitamins not produced by plants that may require supplementation for those eating healthy diets.  Here’s the story.

In terms of longevity, there’s one last supplement to consider: vitamin D. Who votes shorter life? Who votes same life expectancy? Longer life? Vitamin D seems to be the only supplement that will actually make us live longer.

Before we start the next round, I want to note the two vitamins that we can’t get enough of from a healthy diet, and vitamin D is one of them. Vitamin D is made mostly by animals, such as yourself—when you’re exposed to sunlight.

The tiny amounts added to cow’s milk or soy milk isn’t enough for optimal health. There are only two ways to truly get enough—sun or supplements, and it depends where you live.

Basically, no matter how long you sunbathe nude in December and January—in our nation’s capital, for example—the sun’s rays are at such an angle that we don’t make any vitamin D. So, the latest science supports supplemental D during the winter if you’re above LA/Dallas/Atlanta—or, for anyone, anywhere, anytime not getting enough sun.

All right, it’s time for a lightning round question. Before I give you the question, I’ll give you the answer. Anyone?

Okay, the question is: what is the only other vitamin not made by plants? Vitamin B12. It’s not made by animals either, though. It’s made by little microbes, bacteria that blanket the earth. These bacteria grow in the guts of some of the animals people eat, and so their bodies can be sources of B12 for those eating animals.

We likely used to get all the B12 we needed drinking out of mountain streams or well water, but now we chlorinate our water supply to kill off any bacteria. So, we don’t get a lot of B12 in our water anymore; we don’t get a lot of cholera either! So, that’s a good thing!

But in our sanitized modern world, studies continue to show that those eating plant-based diets are simply not getting enough vitamin B12. Is this really a problem? Let me review the medical literature on B12 deficiency just over the last year. 

Keep in mind that it’s so easy to get B12, from either B12-fortified foods or supplements. But like everything else, you actually have to do it.  But you can suffer cognitive decline, or become suicidally depressed because of B12 deficiency.  But, not taking vitamin B12 during pregnancy is inexcusable. It can cause infantile seizures, for example.

Vegan babies should be a lot of things, but floppy is not one of them. It is these negligent vegans that led this year to an official pronouncement from the European Society for Pediatric Nutrition: “Infants and young children should not be fed a vegan diet,” they wrote. Now, what they should have said is, make sure vegan kids get their B12. I mean Dr. Spock even told us to raise our kids with no meat, no dairy.

And the B12 recommendation probably goes for everyone, not just those eating plant-based diets. New studies on the bioavailability of B12 suggest that animal products are not great sources after all. Less than 4% of the B12 in scrambled eggs, for example, is actually absorbed, according to these new studies.

In fact, in modern society, only those eating fortified foods, like breakfast cereal or supplements, seem to be getting enough for optimum health. So, there’s been a renewed call for all grain products in the U.S. to be fortified with B12, like they already do in Israel—which could mean that by law, all bread, all pasta, would have to be enriched with B12, and well, hopefully, never have to hear cases like this ever again.

Sun exposure is associated with lower rates of 15 different cancers and improved cancer survival. In our next story we discover what happens when vitamin D supplements are put to the test.

Johns Hopkins researchers were trying to figure out why states like New Mexico and Arizona had only about half the colon cancer rates of states like New York, New Hampshire, and Vermont. Maybe it’s because they got so much sun. And so, they proposed that maybe the sunshine vitamin—vitamin D—is a protective factor against colon cancer. Since then, sun exposure has been associated with lower rates of 14 other types of cancer, too.

Vitamin D may also affect cancer survival. Higher blood levels of vitamin D were associated with lower mortality of patients with colorectal cancer. How much lower? Like nearly half the mortality. And, the higher the D levels, the lower the death rate appeared to fall. This may explain why the survival rate from colon cancer may depend, on part, on the season of diagnosis—the reason the risk of rapid death is lowest if you’re diagnosed in the fall, after you’ve spent the summer building up your vitamin D stores.

But look; there are other risk factors that could be seasonal, too. Maybe people are taking advantage of the fall harvest, and eating healthier. Maybe that’s why the lower risk in the fall season. Or, maybe there’s more drinking in the winter. And, in the summer, running around outside, not only are you getting more sun; you’re running around outside, getting more exercise—which may itself be protective.

So, these kind of studies just provide circumstantial evidence. Establishing a cause-and-effect relationship between colon cancer and vitamin D deficiency using observational studies is challenging, because of confounding factors like the exercise—so-called “lurking variables.” For example, there may be a tight correlation between ice cream sales and drowning deaths, but that doesn’t mean ice cream causes drowning. A more likely explanation is that there is a lurking third variable—like hot weather, summertime—that explains why drowning deaths are highest when ice cream consumption is highest.

That’s kind of a trivial example. But, this actually happened with hormone replacement therapy. Women taking drugs like Premarin appeared to have 50% less risk of heart disease. And so, doctors prescribed it to women by the millions. But, if you dig a little deeper into the data, yes, women taking estrogen had 50% lower risk of dying from heart disease. But, they also had a 50% lower risk of dying from accidents and homicide. So, it probably wasn’t the drug.

See, the only way to know for sure is to put it to the test, in a randomized clinical trial, where you give half the women the drug, see what happens and, a decade later, they did. And, instead of having a 50% drop in risk, within a year of being given the hormone pills, heart attack and death rates shot up 50%. In retrospect, the lurking variable was likely socioeconomic class. Poor women are less likely to be prescribed hormone replacement therapy, and more likely to be murdered, and die of heart disease. Because of the lurking variable, a drug we now know to be dangerous had appeared protective.

Besides lurking variables, there’s also the possibility of reverse causation. Maybe low vitamin D levels didn’t worsen the cancer. Maybe the cancer worsened the vitamin D levels. This may be unlikely, since tumors don’t appear to directly affect vitamin D levels. But cancer treatment might. Even simple knee surgery can dramatically drop vitamin D levels within hours, thought to be because of just the inflammatory insult of cutting into somebody. So, maybe that could help explain the link between lower D, and lower survival. And hey, if you’ve got cancer, maybe you’re spending less time running around at the beach.

So, yes, higher vitamin D levels are associated with improved survival in colorectal cancer, and in breast cancer. In fact, about double the risk of breast cancer recurrence and death in women with the lowest vitamin D levels. And, vitamin D levels also associated with longer survival with ovarian cancer, and other cancers, like lymphoma. But, bottom-line, as we learned with hormone replacement, is that you have to put it to the test. But, there weren’t a lot of randomized controlled trials on vitamin D supplements and cancer—until now.

We now have a few randomized controlled trials, and vitamin D supplements do indeed appear to reduce the risk of dying from cancer. What dose? The researchers suggest maybe getting blood levels up to at least around 75 nanomoles per liter–levels not reached by as many as three-quarters of women with breast cancer, or a striking 97% of colon cancer patients.

Getting up to these kind of levels, 75, or perhaps even better, 100, might require about 2,000 to 4,000 international units of vitamin D a day—levels of intake for which there appear to be no credible evidence of harm. Regardless of what the exact level is, the findings of these kind of studies may have a profound influence on future cancer treatment.

What are the benefits and risks of taking vitamin C supplements?  Here are some answers. 

Mainstream medicine has long had a healthy skepticism of dietary supplements, extending to the present day. “Enough is enough.” But, this commentary in the Archives of Internal Medicine argued we may have gone too far, as evidenced by our “uncritical acceptance” of supposed toxicities; the surprisingly “angry, scornful tone” found in medical texts, with words like “careless, useless,…indefensible, wasteful, [and] insidious,” as well as ignoring evidence of possible benefit.

“To illustrate the uncritical acceptance of bad news” [about supplements], they discuss the well-known concept that “high-dose [vitamin C] can cause kidney stones.” But, just because something is “well known” in medicine doesn’t mean it’s necessarily true. They couldn’t find a single reported case. We’ve known that vitamin C is turned into oxalates in the body, and if the level of oxalates in the urine gets too high, stones can form. But, even at 4,000 mg of vitamin C a day (that’s like a couple gallons of orange juice worth), urinary oxalates may not get very high.

But, you know, there may be rare individuals that have increased capacity for this conversion into oxalate and, so, a theoretical risk of kidney stones with high-dose vitamin C supplements was raised in a letter printed in a medical journal back in 1973. Okay, but when it’s talked about in the medical literature, they make it sound like it’s an established phenomenon.

Here’s a reference to seven citations, supposedly suggesting an association between excessive vitamin C intake and “the formation of oxalate [kidney] stones.” There were actually studies that followed populations of people taking vitamin C supplements, and found no increased kidney stone risk among men; then later, women, same thing. So, you can understand this author’s frustration that vitamin C supplements appeared to be unfairly villainized.

The irony is that now we know that vitamin C supplements do indeed appear to increase kidney stone risk. This population of men was followed further out, and men taking vitamin C supplements did indeed end up with higher risk—confirmed now in a second study, though also of men. We don’t know if women are similarly at risk, though there’s now also been a case reported of a child also running into problems.

What does doubling of risk mean exactly, in this context? That means those taking like 1,000 milligrams a day of vitamin C may have a 1 in 300 chance of getting a kidney stone every year, instead of a 1 in 600 chance, which is not an insignificant risk—1 in 300. Kidney stones can be really painful; so, they conclude that, look, since there’s no benefits, and some risk, better to stay away.

But, there are benefits. Taking vitamin C just when you get a cold doesn’t seem to help, and regular supplement users don’t seem to get fewer colds. But, when they do get sick, they don’t get as sick, and get better about 10% faster. And, those under extreme physical stress may cut their cold risk in half. So, it’s really up to each individual to balance the potential common cold benefit with the potential kidney stone risk.

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

Be sure to check out my How Not to Die Cookbook, beautifully designed, with more than 100 recipes for delicious and nutritious meals, snacks and beverages. All proceeds I receive from the sale of my books go to charity.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

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 there as a public service, as a labor of love—as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.

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