 Natural immuno-modulators, something that can help regulate our immune system without side effects, has been sought for centuries, and all the while they've been sitting in the produce aisle. Plants produce thousands of active compounds, many of which modulate our immune system enough to protect us from infection. But we can't forget the fungi. Mushrooms have been used for centuries as folk remedies, and for good reason. Some have been shown to boost immune function as well. So much so, a type of fiber-founded shiitake mushrooms is approved for use as adjunct chemotherapy injected intravenously to help treat a variety of cancers by rallying our immune defenses. Within 6,000 papers have been published on these so-called beta-glucans, but almost all the data about preventing infections has come from Petri dish or lab animal studies until a few years ago, when a series of experiments on athletes showed beneficial effects. But that was in, like, marathon runners. What about the rest of us? We didn't know until now. Beta-glucan fiber, found in bakers, brewers, and nutritional yeast, helps to maintain our body's defense against pathogens, even in non-athletes, according to this double-blind, randomized placebo-controlled trial, reducing the incidence of infections by the common cold by 25%, those that ate the equivalent of about a spoonful of nutritional yeast today, and had fewer cold-related sleeping difficulties if they did get sick. With about half a spoonful a day's worth, still worked big drop in common cold incidents and a reduction in symptoms as well. Why, though? This study found that not only were upper respiratory infection symptoms diminished, but that mood states appeared to be improved, like a significant boost in feelings of vigor. So they suggest 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 stomach aches, but they were both in the placebo group. Unlike antibiotics and antivirals, which are designed to kill the pathogen directly, these 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 that them is foreign. But if it's treated like an invader, might it trigger an inflammatory response? Turns out it 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 the inflammatory component. So oral intake can be considered safe and effective. Note they said oral intake, though I would not recommend injecting nutritional yeast into your veins, no matter how much you like the stuff. 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 for everyone else, is there any downsides? Well, if you look at some packages of nutritional yeast, in California some are slapped with Prop 65 warning stickers, suggesting that 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 a half a microgram of lead per daily serving. So I contacted the 6 brands I knew about and asked them how much lead was in their products. Cal originally said less than 5 parts per million, but then when we called back they said less than 3 parts per million. But even if it's 3, that translates into less than 45 micrograms per serving nearly 100 times more than the California limit. But perhaps better than Bob's Red Mill or Frontier Co-op, who evidently didn't test at all. At least they got back to me. Red Star brand failed to respond to multiple attempts to contact them. Now foods said, of course we test for lead. That's nice. And claim that at least their recent batches meet the less than half a microgram California standard. Unfortunately, despite repeated requests, they did not provide me with documentation to substantiate those numbers. My favorite response was from Braggs, who sent me the analysis certificate from the lab, showing less than 0.01 parts per million, 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 like 2 micrograms a day in the form of lollipops. But as far as I'm concerned, the less lead, the better.