Exploring the science behind popular immune-boosting nutrients and remedies. Which supplements like vitamin D, vitamin C, and zinc have evidence-based benefits, how the microbiome influences immunity, and why practices like good hygiene, sleep, and stress management matter most.
Exploring the science behind popular immune-boosting nutrients and remedies. Which supplements like vitamin D, vitamin C, and zinc have evidence-based benefits, how the microbiome influences immunity, and why practices like good hygiene, sleep, and stress management matter most.
Mentioned in this episode:
Vitamin C reduces the severity of common colds: a meta-analysis | BMC Public Health | Full Text
Nutrition Diva #787 - Sunscreen vs. Vitamin D: Finding the right balance
Nutrition Diva is hosted by Monica Reinagel, MS, LDN. Transcripts are available at Simplecast.
Hi, and welcome to the Nutrition Diva podcast, a show where we take a closer look at nutrient research, headlines, and trends so that you can make more informed decisions about what you eat. I’m your host, Monica Reinagel, and as we head into another cold and flu season, you’re probably hearing a lot of talk about “boosting” your immune system. There are a lot of supplements that claim to help you ward off colds and other respiratory infections. But what does the science say?
We often think about boosting immune function as being similar to the way you might turn up the volume on your speakers. But that’s not really how it works.
The immune system is not just a single thing. It’s a whole orchestra of different types of cells and chemical messengers that respond to different types of threats in a lot of different ways. Instead of that single volume knob, picture a giant mixing board with dozens of knobs and sliders that control different frequencies and aspects of the sound, all working together to produce a harmonious effect.
In other words, simply saying that a specific nutrient or an herb boosts immune function doesn’t really tell you very much. Furthermore, just because a nutrient is involved in some aspect of the immune response, it doesn’t necessarily follow that taking large amounts of that nutrient will boost your immunity. In fact, excessive amounts of some of these “immune boosting” nutrients could even end up suppressing immune response.
That said, I hate colds as much as anyone else. And, as an aside, although facial masks are no longer as ubiquitous as they were during the height of the COVID-19 pandemic, I still keep them on hand. They are actually very effective in preventing transmission of air-borne viruses, such as those that cause the common cold. And if I find myself in close quarters with someone who has obvious symptoms (sitting next to them on a plane or at a concert, for example), I am thrilled to have access to such an easy and convenient way to protect myself. I have a lot fewer colds than I used to and I think this is a big part of the reason why.
But, I digress. As I was saying, I hate colds as much as anyone else. So, I can certainly sympathize with anyone who finds themselves tempted by products promising to make them less susceptible to seasonal sniffles. So, let’s take a look at those that actually have some science to support them and how they are best used.
Low vitamin D levels are linked to a higher risk of respiratory infections–and levels often dip in the winter when our exposure to sunlight is limited. And there’s even research to suggest that taking a vitamin D supplement might reduce the severity of infections if you do catch a cold or flu.
So, this winter, you might want to focus on getting enough vitamin D, either from foods or a supplement. Food sources include oily fish, milk (which is fortified with vitamin D), liver, and egg yolks. And, as I mentioned in a recent episode, mushrooms can also be a good source of vitamin D if they’ve been exposed to natural sunlight.
Vitamin C has long been a go-to supplement for cold prevention. Unfortunately, vitamin C doesn’t seem to reduce the likelihood that you’ll catch a cold. But, as with vitamin D, taking a vitamin C supplement might shorten the duration and severity of symptoms. There is a catch, however. You can’t wait until you feel the first signs of a cold to start pounding the vitamin C. It only seems to help if you’re getting a good dose of C on an ongoing basis.
Vitamin C is also one of those nutrients that is not stored in the body. So, ideally, you want to have some vitamin C rich foods in your diet every day. Citrus fruit, strawberries and kiwi are all good sources, but so are green peppers, broccoli, Brussels sprouts, cabbage, and even potatoes!
Zinc lozenges may help reduce the duration of cold symptoms–and, unlike vitamin C, they are effective if taken at the first sign of illness. And, in fact, this is one you want to keep up your sleeve (with your spare kleenex) until you actually need it. Sucking on zinc lozenges all the time can actually make them less effective in this regard.
I have also used them for 24 hours or so after being exposed to someone with obvious cold symptoms, even if I didn’t feel sick myself. Taking zinc as a dietary supplement (or eating foods rich in zinc) does not help reduce cold symptoms, by the way.
You might also remember zinc nasal sprays for cold prevention. These have largely been discontinued because there is a risk of permanent damage to your sense of smell. Brands that sell zinc lozenges may still sell nasal sprays, but they no longer contain zinc. If you have an old bottle of zinc nasal spray lying around, it’s probably time to toss it out.
We’re also hearing a lot more about the role of the microbiome (the beneficial bacteria that live in our gut) in immune health. One of the many benefits of cultivating a healthy gut population is a strong immune system. Eating fermented and cultured foods, such as yogurt, kefir, kimchi and other fermented vegetables is a good practice. But eating a variety of fiber rich foods may be even more impactful.
But, what about taking a probiotic? There is a limited amount of evidence that probiotic supplementation might modestly reduce cold symptoms. The trick here is that these studies look at very specific strains of bacteria and it's really hard to extrapolate those results to the hundreds of different probiotic supplements on the market.
Interestingly, some of the research seems to suggest that the beneficial bacteria in the mouth and oral cavity (as opposed to the gut) may be key to improving our defenses against colds and other respiratory infections. I was intrigued by a https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.789063/fulls, featuring a strain called thermophilus K12, were found to reduce respiratory tract infections.
You can also promote a healthy oral microbiome by brushing and flossing regularly, avoiding sugary foods and drinks, and drinking plenty of water. Many oral health experts also advise against using mouthwashes containing alcohol, as these decimate all the bacteria in your mouth, including the beneficial microbes and not just the bacteria that cause tooth decay and gum disease.
Finally, we should talk about elderberry and echinacea, two popular herbal remedies. Neither one appears to be very helpful in preventing infection. But both have some research supporting their use in reducing the duration and severity of symptoms. So these are also remedies that you want to save for when you either think you might be getting sick or, potentially, for times when you feel like you might be at increased risk, such as when you’re traveling or under stress. But they’re probably things that you want to take every day on an ongoing basis.
Many of us have a specific protocol that we turn to when we’re coming down with something. It might be echinacea and vitamin C, it might be elderberry syrup and garlic, or perhaps zinc lozenges and ginger tea.
Whatever our particular protocol is, we believe that it helps. And, honestly, that belief may actually be part of the magic. Taking positive action helps us feel a little bit more in control of the situation, and that in and of itself (plus our optimism) can make us feel better. In other words, the placebo effect is real. Why not take advantage of it?
And finally I should point out that nutrition is just one piece of the puzzle. Other things that can reduce your chances of getting sick and help you bounce back more easily if you do include getting enough sleep, managing stress, and regular exercise. Finally, don’t underestimate the power of good hygiene practices: Frequent handwashing, avoiding close contact with sick individuals, and trying not to touch your face can all reduce the likelihood of getting a pesky cold this season.
I hope this helps clear up some of the confusion around immune-boosting foods supplements, and gives you some actionable tips for staying healthy this season. If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206
Nutrition Diva is a Quick and Dirty Tips podcast. Our team includes Brannan Goetschius, Nathan Semes, Davina Tomlin, Holly Hutchings, and Morgan Christianson and Nathaniel Hoopes.
That's all for this episode. Thanks for listening! I'll see you next week.