Natural immunomodulators that can help regulate our immune system without side-effects have been sought for centuries, and all the while they've been sitting in the produce aisle. Plants produce thousand of active compounds, many of which modulate our immune system, but we can't forget the fungi (see Boosting Immunity While Reducing Inflammation).
Mushrooms have used for centuries as folk remedies, and for good reason. Some have been shown to boost immune function, so much so that a type of fiber found in shiitake mushrooms is approved for use as adjunct chemotherapy, injected intravenously to help treat a variety of cancers by rallying our immune defenses.
More than 6,000 papers have been published on these so-called beta glucans, but almost all of the data about preventing infections had come from petri dish or lab animal studies, until a few years ago when a series of experiments on athletes showed beneficial effects in marathon runners (see Preserving Immune Function in Athletes With Nutritional Yeast). What about the rest of us? We didn't know... until now.
As I explore in my video, Nutritional Yeast to Prevent the Common Cold, beta glucan fiber found in baker's, brewer's and nutritional yeast helps to maintain our body's defense against pathogens even in nonathletes, according to a double-blind, randomized, placebo-controlled trial. The recurrence of infections with the common cold was reduced by 25% in those that ate the equivalent of about a spoonful of nutritional yeast a day, and had fewer cold-related sleeping difficulties when they did get sick.
What about half a spoonful a day? Still worked! Subjects experienced a big drop in common cold incidence and a reduction in symptoms as well. Why is this? This study found that not only were upper respiratory infection symptoms diminished, but that mood states appeared to improve, for example a significant boost in feelings of "vigor." So the researchers suggest that maybe the yeast fiber is able to counteract the negative effects of stress on the immune system.
In terms of side-effects, two folks reported stomachaches, but they were both in the placebo group.
Unlike antibiotics and antivirals, which are designed to kill the pathogen directly, these yeast compounds instead appear to work by stimulating our immune defenses, and as such don't share the same antibiotic side effects. They stimulate our immune defenses presumably because our body recognizes them as foreign. But if it's treated like an invader, might it trigger an inflammatory response? Turns out these fiber compounds may actually have an anti-inflammatory effect, suggesting nutritional yeast may offer the best of both worlds, boosting the infection fighting side of the immune system while suppressing inflammatory components.
Yeast is high in purines, so those with gout, uric acid kidney stones, and new organ transplant recipients may want to keep their intake to less than a teaspoon a day. But is there any downside for everyone else? In California some packages of nutritional yeast are slapped with prop 65 warning stickers, suggesting there's something in it exceeding cancer or birth defect safety limits. I called around to the companies and it turns out the problem is lead. California state law says a product cannot contain more than half of a microgram of lead per daily serving, so I contacted the six brands I knew about and asked them how much lead was in their products.
KAL originally said "<5 ppm," but when we called back they said "<3 ppm." Even if it's 3, that translates into less than 45 micrograms per serving, nearly a 100 times more than the California limit. But perhaps that's better than Bob's Red Mill or Frontier Coop, who evidently don't test at all. But at least they got back to me. Redstar brand failed to respond to multiple attempts to contact them. Now Foods said they test for lead and claim that at least their recent batches meet the less than a half a microgram California standard. Unfortunately, despite repeated requests they would not provide me with documentation to substantiate their numbers. My favorite response was from Bragg's who sent me the analysis certificate from the lab showing less than 0.01 ppm, which means at most less than half the California standard, which I believe is the most stringent in the world. To put the numbers in context, in determining how much lead manufacturers can put into candy likely to be frequently consumed by small children, the Food and Drug Administration would allow about 2 micrograms a day in the form of lollipops, but as far as I'm concerned the less lead the better.
I was so frustrated by the lack of transparency I decided to test them for lead myself. NutritionFacts.org hired an independent lab to conduct our own tests for lead and shipped out 8 samples of nutritional yeast in their original package. The lab used standard practices for lead testing known as Official Methods of Analysis set by AOAC International. Lab technicians determined the lead values based on California Prop 65 standards. Here are the results from the brands we tested:
Bob's Red Mill - Test report shows no detectable lead (<0.01 ppm).
Bragg - Test report shows no detectable lead (< 0.01 ppm).
Dr. Fuhrman - Test report shows no detectable lead (< 0.01 ppm).
Frontier Coop - Test report shows lead levels at 0.021 ppm. It would take six tablespoons a day (based on the manufacture's listed density) to exceed the California Office of Environmental Health Hazard Assessment Maximum Allowable Dose Level (MADL) for chemicals causing reproductive toxicity.*
KAL - Test report shows lead levels at 0.011 ppm. It would take seven tablespoons a day to exceed the MADL.*
NOW Foods - Test report shows no detectable lead (< 0.01 ppm).
Red Star - Test report shows no detectable lead (< 0.01 ppm).
Whole Foods - Test report shows lead levels at 0.012 ppm. It would take six tablespoons a day to exceed the MADL.*
So what do all those numbers mean? None of the brands tested exceeded California prop 65 standards. No matter what brand, consuming a typical serving (2 tablespoons) per day is still well within safe limits.
Michael Greger, M.D.
PS: If you haven't yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:
- 2012: Uprooting the Leading Causes of Death
- 2013: More Than an Apple a Day
- 2014: From Table to Able: Combating Disabling Diseases with Food
- 2015: Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet
- 2016: How Not To Die: The Role of Diet in Preventing, Arresting, and Reversing Our Top 15 Killers
* The Maximum Allowable Dose Level for lead as a developmental toxin is 0.5 micrograms a day. How are MADL's calculated? Basically scientists figure out what the "no observable effect level" is, the level at which no birth defects or reproductive toxicity can be found, and then introduce a 1000-fold safety buffer. So for example, let's say there's some chemical that causes birth defects if expectant moms are exposed to two drops of the chemical a day, but there's no evidence that one drop a day is harmful. Do they set the Maximum Allowable Dose Level at one drop? No, they set it at 1/1000th of a drop to account for scientific uncertainty and to err on the side of caution. So by saying six tablespoons a day of nutritional yeast may exceed the MADL is in effect saying that the level of lead found in 6,000 tablespoons of nutritional yeast may cause birth defects. Like mercury, though, as far as I'm concerned the less lead exposure the better. I hope this will inspire companies to do further testing to see if the levels we found were just flukes.
Image Credit: Sally Plank / Flickr. This image has been modified.