Category Archives: Colds and Flu

Combating the Common Cold: What Herbals Work?

Isn’t it humbling that we have no cure for the world’s most common illness? Yes, the common cold, globally the #1 cause of sick days and doctor visits, still stampedes across the world, blissfully immune to any Eastern or Western prescriptions. As a family doctor, I’m always a bit frustrated that I can’t offer much to these patients, at least in terms of Western allopathic medicines. So, I decided to scour the literature again to see if any new research has shown benefits from herbals and supplements. And the good news is yes: there may actually be a couple of supplements which can help you get better, quicker. Here’s my advice below. (Please note that this research is for treating, and not preventing, colds and flu.)

Evidence-Based Literature Search

When it comes to supplements and natural therapies, I use only a tiny handful of resources that I consider trustworthy. All are certified by the Health on the Net Foundation as sources of trustworthy medical information. All these sites would review only the best, most unbiased research, which usually means the gold standard of all research: placebo-controlled, randomized controlled trials. I strongly recommend that everyone use HONCode’s search engine anytime you’re looking for medical advice, especially regarding supplements. For example, you’ll never see the anti-vaccine snake-oil salesman Dr. Mercola on their list. Here are my favorite medical resources, and their evaluations of therapies for the common cold:

A graphical image and time line for cold symptoms. Note how the cough is always the last to improve…


Let’s break it down into the supplements that have the most evidence:

  • Zinc: This seems to have the most support, especially higher doses (>75 mg daily) of lozenges containing zinc gluconate or zinc acetate. Some good studies show reduction in cough, runny nose, headache, sore throat and overall time of illness. But side effects are common, especially nausea and a bad taste in the mouth. Also, definitely do not do the zinc nasal sprays, which have clear evidence to permanently cause loss of smell. The data suggests you should stick with lozenges and not pills. I see a few brands of logenzes up to 23 mg each, which at three times a day would help. The test results from ConsumerLab show 23 mg in Nature’s Way Zinc lozenges, and 13.8 mg in Cold-Eeze Cold Remedy Lozenges (but much more expensive). I see a few popular brands with only 5 mg zinc each, which seems far too low to work. I wouldn’t advise using these for children.
  • echinaceaEchinacea: This is probably the one you’ve heard about, and the evidence is encouraging — but not totally clear. Some “double-blind, placebo-controlled studies have found that various forms and species of echinacea can reduce the symptoms and duration of a common cold, at least in adults. The best evidence is for products that include the above-ground portion of E. purpurea rather than the root.” But it’s very difficult for me to recommend a proper dose, as studies have used multiple regimens via drops, pills and teas, also using many types of echinacea, as well as different combinations of root and plant. Here’s a useful list of test results from ConsumerLab showing which brands in the USA have proper amounts of the herb.
  • andrographisAndrographis peniculata: An Indian herb very popular in Ayurvedic medicine and now in Europe, I think this actually has some good evidence.  A handful of double-blind, placebo-controlled have shown benefit in reducing the duration and severity of cold symptoms, especially cough. An excellent meta-analysis of herbals from Germany showed significant improvement in severity and duration of a cough, especially via liquid formulation. The usual dose seems to be 48-500mg of the andrographolide aerial parts, usually divided three times a day. You can find a good list of andrographis brands on I keep reading about a Swedish patented combination with eleutherococcus and sambucus (Kan Jang Plus), but I don’t see it sold anywhere in the USA.
  • pelargonium-409238_960_720.jpgPelargonium sidoides (Umckaloabo): This is an interesting herbal, very popular in Europe and perhaps should be more popular here in the USA. That same German meta-analysis I mentioned above found strong evidence that it helped with cough, fevers, and sore throat — including for children as young as one year old, although the German independent Institute for Quality and Efficiency in Health Care says it shouldn’t be used for children under six years. The Cochrane Library also reviewed this herb and concluded, “P. sidoides may be effective in alleviating symptoms of acute rhinosinusitis and the common cold in adults, but doubt exists.” As with andrographis, the liquids and syrups were better than tablets. I see on iHerb a series of pelargonium products called Umcka with good reviews.
  • Probiotics: Probiotics actually have pretty good evidence that taking them for months, especially over the winter, can markedly improve both the frequency and the severity of colds — for kids and for adults (as does vitamin D). That’s great news! But for symptom relief during a cold, the evidence is much more scant. I couldn’t find one good study for this; none of the groups above recommend probiotics as treatment.
  • Vitamin C: Here’s another super popular supplement, which many people swear by. But again the evidence isn’t conclusive, and the few studies that do show a benefit show only mild improvement. Still, at least it seems safe for adults and children, and evidence is even stronger as a preventive during the cold seasons.


My Bottom Line

For immune boosting,  don’t forget the most important advice: get a good’s night sleep; eat a lot of anti-oxidant foods; and stay well hydrated.

In terms of supplements, I think it’s appropriate for adults (not kids) to try some of the above supplements — and the sooner, the better, within 24 hours of your symptoms starting.

For what it’s worth, here’s my plan for myself and my wife the next time we get a cold: we’re going to continue our usual vitamin C + zinc bursts, usually using Airborne effervescent tablets, three times a day. Emergen-C and Wellness Formula also are similar, all three with a ton of vitamin C, some zinc and an assortment of herbals, many of which are mentioned above. I’m also adding andrographis 400mg twice a day and also pelargonium; and I’ll continue doubling up on my probiotic supplement, despite the lack of evidence. (One small note: last week my wife tried andrographis for the first time and had a horribly itchy rash for days. I was fine.)

In general, for children, I’m still hesitant about using any of these herbals for children under 6 years old, and I remain cautious about what I use with my own kids, both under 4 years of age. I still like probiotics during a cold, and I’m a big fan of honey for cough for all ages above one year, which studies show works better than any OTC syrup. I’m encouraged with the European studies using pelargonium and also ivy/primrose/thyme syrups, some of which are partially included in American brands like Zarbees. For more age-specific advice, please look at the recommendations in my previous article about curing a cough.

What herbals and supplements have you used? Please leave comments below.


Curing a Cough: What’s the Best Medicine?

Coughing from a cold or flu is probably the most frustrating symptom we can have — for children, their parents, and even the doctor treating them. Why? Because there’s honestly very little that we can do to treat it. That’s a hard pill to swallow, and it’s especially humbling for me as a family physician. But it’s also very frustrating for me as a father of two toddlers, as they just started daycare and are fighting new viruses every week. As we comfort them at two in the morning with a hacking cough, I’ll face same question from my wife as from parents in my clinic: “which cough syrup should we use?”

First, it’s important to note that a cough is generally a good thing. It’s our body’s natural attempt to get germs and toxins out of our bodies, so it’s not such a healthy idea to suppress the cough too much. Of course, a cough can become too severe, or painful, and lack of sleep isn’t good for anyone’s immune system. So in terms of that, I think it’s reasonable to try something safe. But it’s clear that no matter what you use, nothing makes a cough completely go away for more than a couple of hours. And it’s also important to note from the graph below that the cough is always the last symptom to get better, and may linger even for a couple of weeks.

a graphical image and time line for cold symptoms

Having said that, I’d like to help you cut through the confusion at your pharmacy and make this simple: don’t bother with almost any of the OTC cough syrups. First, try some honey.

Your pharmacy shelves have a bewildering assortment of cough and cold medicines. It’s confusing for me as well, even with my training! Overdosing is quite a problem, especially for children. In fact, drug makers in 2008 voluntarily changed their warning labels (with a gentle push from the FDA), pulling off the shelves all cough medicines used for children under two years old, and changing warning labels to say “do not use in children under 4 years of age” (you can read the FDA statement here). The American Academy of Pediatrics is even more strict: no OTC cough medicines for any child under 6 years old, and caution from ages 6 to 12. The major concern has been the number of overdoses, even deaths, in children taking too much of these medicines — especially acetaminophen, otherwise known as Tylenol, which is added for pain and fever relief. In a proper dose it works wonderfully, but in high doses it causes liver failure.

Not only are these medicines potentially dangerous, they also barely work anyway. For example, the decongestant phenylephrine, which is now in almost every combination medicine, is no better than placebo in the best research results. In other words, there’s a good reason your runny nose isn’t getting better — it’s because the medicine doesn’t work. This medicine a couple of years ago replaced the far more effective drug pseudoephedrine — but this is now only behind the pharmacy counter, because people were buying pseudoephedrine-containing pills in bulk and cooking it down to make methamphetamine. So if you really want sinus relief, you have to ask the pharmacist for pseudoephedrine. It’s still OTC, so you don’t need a prescription from your doctor, but you’re only allowed two boxes.

The bright side to all this is that the most useful cough syrup may be in your home right now. It’s honey! A Cochrane database review from 2014 showed that honey helped better than dextromethorphan and also diphenhydramine for cough frequency, severity and quality of sleep, for children and their parents, with minimal side effects.

My advice for a cough in different age groups is as follows:

Age one and under: no OTC syrups are safe, including honey, which carries the risk of botulism. The best advice is to take care of the cause of the cough, often from post-nasal drip, by using nasal saline drops or spray. A bedroom humidifier can also help if the room is too dry, especially in cold winter nights. Probiotics also can be helpful, as a growing number of studies are showing their effectiveness in reducing duration of a cold, less severe symptoms, and less time away from school or work. The best research is on bifidobacteria and Lactobacillus GG probiotics. Also, don’t forget to get the annual flu shot for any child over 6 months of age. If they’re younger, they’re vulnerable to get the flu — which is why it’s even more important that all caretakers and family members get the annual flu shot, so they won’t pass along the flu virus to the baby. Coughing can also cause pain from a sore throat or rib inflammation, so if your baby is fussy but has no fever, they may be in pain, so don’t be afraid to give them ibuprofen or acetaminophen syrups for comfort (and better sleep).

Ages 1-6: I think honey or honey-based herbal mixtures (not homeopathic) should be the first choice for a cough. Probiotics should also be used during the illness. Taking care of nasal congestion often can help decrease a cough, again including the safe remedy of nasal saline rinsing. As a second choice of syrups, a cough syrup containing only dextromethorphan could also help a bit, as was shown in that Cochrane review from 2014. This medicine is the “DM” part of many labels.

Ages 6-12: Again, honey-based syrup is not only the most effective but also the safest choice. At this age, the risk-benefit ratio of other treatments becomes more favorable, including my favorite nasal decongestant combination: pseudoephedrine pills and oxymetazoline nasal spray. Probiotics during the illness also are helpful. But don’t forget that many doctors would still be hesitant to recommend any OTC medicines until 12 years of age. Also, while the oxymetazoline nasal spray works rapidly for nasal congestion, never take it for more than 5 days in a row, otherwise you can develop rebound nasal congestion and could become dependent on it (we call it “Afrin addiction”).

Ages 12 and up: We’re finally at the “adult” age where most OTC medicines at least are safe to use, whether or not they’re effective. I would still stick with honey syrup, and the decongestants as I mentioned above. Again, don’t forget about probiotics. Also, don’t forget about common sense items such as a healthy amount of sleep, as well as foods full of antioxidants, and light exercise to boost your immune system. In terms of natural medicines, elderberry syrup has some evidence to help decrease symptoms of the flu.

Ages 65 and older: Here we start getting cautious again with OTC medicines, as many might have unwanted side effect combinations with the prescribed medicines for chronic diseases that many elderly people take. As we get older, we can’t fight off infections as well as we could when younger. So it’s important not to get sick in the first place — with the annual flu vaccine, as well as the pneumonia vaccines. If you do get a cold, some OTC medicines may cause more side effects in the elderly, such as dangerously high blood pressure from pseudoephedrine, or confusion, urinary retention and lethargy from diphenhydramine. I would focus on honey or dextromethorphan syrups, and nasal saline spray for a decongestant.

Which OTC medicines don’t work at all, at any age? I would advise not to use any homeopathic remedies, such as Oscillococcinum or Zicam, which may seem appealing to many but literally have no evidence of effectiveness, as you would expect from a product which by definition has zero molecules of any active drug. The FTC recently issued an enforcement requiring homeopathic labels to state ” (1) There is no scientific evidence that the product works and (2) the product’s claims are based only on theories of homeopathy from the 1700s that are not accepted by most modern medical experts.” And it’s also dangerous to assume that homeopathic medicines are safer, as noted by this winter’s warnings by the FDA against homeopathic teething tablets, which tests show may have toxic amounts of belladonna, and which could be related to ten deaths of infants. Clearly this is a case where the risks far outweigh benefits.

For more information about treating the common cold, you can read my family practice academy’s parent handout about treating the common cold in children ; and more articles about the common cold at my wellness blog at MyFamily Health Guide.


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Antibacterial Soap: As Useless As Your Multivitamin

Hand washingIt hasn’t been a good week for a couple of daily household items common in millions of homes across the world. First we had nail-in-the-coffin proof that our daily multivitamins are useless for the great majority of people in preventing any disease or prolonging life. Now we find out that antibacterial soaps not only are useless but possibly harmful, and the FDA may step in and regulate the entire industry. There goes half of my Christmas stocking stuffers!

Let’s be clear here that the FDA is specifically referring to the consumer products which contain the pesticide chemical called triclosan. The alcohol-based hand washes are still considered effective and safe. So what is the FDA so worried about? In their Consumer Update this week, they have three concerns:

  1. Triclosan looks to be an endocrine disruptor in animal studies, getting absorbed and messing around with hormones in ways we’re still unclear about  (the same concerns behind BPA and other chemicals)  — but concerning enough that most companies have already started to bow to consumer pressure and are already phasing triclosan out.
  2. Triclosan use makes the surviving bacteria stronger, leading to resistance in the community. So when you actually have a real bacterial infection and might need antibiotics for real, your pills may no longer be effective.
  3. Triclosan levels are popping up in the general community and literally downstream from waste plants, and given the possible endocrine harm, it may be a good idea to limit future exposure.

Perhaps most importantly, there is zero evidence that triclosan soaps wipe out more bacteria than simple soap and water! The FDA now is going to require companies selling such soaps and body washes to provide actual data showing not only that they wipe out bacteria, but that they don’t breed resistance. Plus, they will have to prove that they are more effective than simple soap and water. Such studies are very expensive, likely drying up most of this market. I say good riddance. It was always pure marketing, anyway, with plenty of warnings from public health researchers about potential harm. Here is a scary quote from the FDA (via a Wired article) about the potential hormonal harm:

…triclosan is an antiseptic active ingredient commonly found in consumer antiseptic hand and body wash products. It is absorbed through the skin and has been found in both human breast milk and urine. Further, triclosan has been found at relatively consistent levels in urine samples collected from a representative sample of the U.S. population since sampling began in 2003. We believe that the consequences of this systemic exposure need to be assessed.

One effect of systemic exposure to consumer antiseptic wash ingredients that has come to our attention since publication of the 1994 TFM is data suggesting that triclosan and triclocarban can cause alterations in thyroid, reproductive, growth, and developmental systems of neonatal and adolescent animals. Hormonally active compounds have been shown to affect not only the exposed organism, but also subsequent generations. These effects may not be related to direct deoxyribonucleic acid (DNA) mutation, but rather to alterations in factors that regulate gene expression.

A hormonally active compound that causes reproductive system disruption in the fetus or infant may have effects that are not apparent until many years after initial exposure. There are also critical times in fetal development when a change in hormonal balance that would not cause any lasting effect in an adult could cause a permanent developmental abnormality in a child.

The sad point about all of this is that we’re all usually buying these products to protect us from colds and flu — almost all of which are caused by viruses, and not bacteria. Thus, the triclosan is useless in the first place!

My advice? Throw away any of your home products with triclosan, and stick to soap and water. And throw a small alcohol-based hand gel into your day bag. It’s all too common around here not to find any soap in the bathrooms…or running water…or hand towels…or all three…and don’t get me started on the toilet paper issue…

Preventing Colds and Flu For Your Kids

It’s cold and flu season yet again, and time to review the simple steps can we all take to avoid these inevitable illnesses. This year’s flu season is a bit more newsworthy than usual as H7N9 bird flu continues to pose a potential threat. But it doesn’t change much how to protect yourselves from this or any other flu, except for a few obvious warnings to avoid touching raw poultry, petting zoos and other basics.

influenza symptoms cold prevention children
Source: wikipedia

The most common sense preventive measure is hand washing. This is a crucial, simple idea that has been proven for almost 200 years, ever since Dr Lister proved that hand washing with antiseptic dramatically cut down on surgical infections (be thankful you didn’t live back then!). Simple soap and water does the trick — but I also like the alcohol gels as they work quicker and wipe out a much larger percentage of viruses and bacteria than soap.

Another interesting idea is daily gargling, with simple salt water, during the entire winter season. People who gargle up to three times a day have a 40% decrease in respiratory illness and symptoms during the winter. Gargling also is a simple way to help improve sore throat pain and swelling, and it also loosens up mucus.

Another method with good evidence for prevention is a daily supplement of vitamin D, for all ages, during the entire winter season. Daily year-round doses of vitamin D (400 IU for children) are recommended by the American Academy of Pediatrics. Studies show that schoolkids who took a higher dose of vitamin D during flu season had a 42% decrease in influenza infections. I also recommend vitamin D for adults daily here in Beijing, certainly in the winter months and probably all year, as the air pollution cuts down on the needed sunlight that hits our skin and creates vitamin D.

Simply getting a good night’s sleep can also decrease your risk of infections. People who sleep only 6-7 hours a night are three times more likely to get cold symptoms than those who have 8 or more hours of sleep. Proper sleep is crucial for our immune system. Perhaps those of you who feel you “always get colds in Beijing” should check into your sleep patterns!

Many of us try herbal treatments to prevent colds, and you can find good data on effective prevention from the Natural Medicines Database at Their highest level of support is American ginseng, listed as “possibly safe and effective”. Garlic, ALA, lactobacillus and others have “insufficient evidence”. You will probably be surprised to find that the most commonly used preventive medicines such as echinacea, vitamin C and zinc all are considered “possibly ineffective”.

And of course I must mention the flu vaccine, which is officially indicated for anyone, healthy or sick, after six months of age. It’s not 100% effective for many people, but I feel the benefits far outweigh the risks. Those of you with any contact with newborns and infants under six months of age should seriously consider getting the vaccine for yourselves, as those infants are most vulnerable to the flu, and they are not eligible for the vaccine.

Don’t forget the basic steps for a healthy immune system, via exercising, a good diet full of antioxidants, and not smoking!


This article was initially published in my monthly Beijingkids column. 

Natural Ways To Prevent H7N9 And Other Viruses

What can you do right now to prevent getting the flu? As H7N9 continues to dominate our health headlines, I thought I’d continue my refresher course on prevention of this and other viruses. I’ve already discussed the specific tips for preventing H7N9 bird flu as well as getting a good night’s sleep; now let’s go over the actual evidence for the many herbal and non-prescription methods to prevent colds and flu. With herbal treatments, my favorite source is always from the Natural Medicines Database. They have an outstanding free article researching the best evidence for every common herb that people use to fight colds and flu. They also have a terrific graph at the end which summarizes the data. Here is a screenshot:

Natural Medicine for Flu and Cold Prevention
Natural Medicine for Flu and Cold Prevention

As you can see, there is nothing in their green zone of therapies proven “likely safe and effective”. Their highest level is American ginseng, listed as “possibly safe and effective”. Then we have a slew in the “insufficient evidence” pile including ALA, garlic, lactobacillus and others. You will probably be surprised to find that the most commonly used preventive medicines such as echinacea, vitamin C and zinc all are considered “possibly ineffective”, lower than many other herbals. You’re welcome to disagree, but they always back up their findings from a continuing review of the latest research. Here is a snippet of their details:

Echinacea is widely used to prevent upper respiratory infections including colds and flu. In vitro research suggests that echinacea stimulates the immune system, causing macrophages to produce tumor necrosis factor, interleukin-1, and beta-interferon.6388,6389 Echinacea has been studied for prophylaxis against the common cold, but has consistently been shown to be ineffective.3281,3282,6386,6417,8228,10782,12354,13419,14419 Don’t recommend echinacea for PREVENTING colds and flu.

American ginseng might also be beneficial. Some evidence suggests that taking a specific American ginseng extract called CVT-E002 (Cold fX, Afexa Life Sciences, Canada) 200 mg twice daily over a 3-4 month period during influenza season might decrease the risk of developing symptoms of an upper respiratory tract infection such as the common cold or flu in adults aged 18-65 and older.11351,13192,14345 It might not reduce the chance of getting the first cold of a season, but might reduce the risk of getting repeat colds in a season.13192 When respiratory infections do occur, this extract seems to reduce the symptom severity and duration of symptoms.13192,14345 More evidence is needed to confirm these findings before American ginseng can be recommended for this use.

Probiotics are gaining interest for reducing the risk of upper respiratory tract infections such as the common cold. Some research suggests that milk fortified with a specific strain of probiotic, Lactobacillus rhamnosus GG (Culturelle) seems to modestly reduce the incidence of respiratory infections in young children in day care.8565 Lactobacillus GG seems to stimulate some measures of immune function.7756,7757 Some clinical research also shows that children attending day care who drink a milk product containing a specific combination of Lactobacillus acidophilus plus Bifidobacteria animalis (HOWARU Protect, Danisco) for 6 months have a 45% lower risk of developing flu-like symptoms compared to placebo. This is promising, but still preliminary.

Zinc inhibits rhinovirus replication in vitro, but there’s no evidence this happens in vivo. Some evidence suggests that zinc might also increase cell-mediated immune response in elderly people. But there’s also no reliable evidence that taking zinc supplements can help prevent a cold.10780,10783,10784 Zinc also does not seem to decrease the chance of getting the flu in vaccinated, institutionalized elderly patients.6563

Vitamin C has long been promoted for colds and flu and has generated lots of controversy over the years. Vitamin C might help immune function. It seems to increase T-lymphocyte activity, phagocyte function, leukocyte mobility, and possibly antibody and interferon production.1963,1965 But most evidence suggests that even in doses up to 1 gram/day, vitamin C does NOT prevent colds.1966,1967,1968,1987,3042,6458,7101,9832 Likewise, increasing DIETARY vitamin C intake does not seem to affect the risk of getting a cold.10780

What Else Works?

The most common sense preventive measure by far is hand washing. This is a crucial, simple idea that really does cut down on passing along the infection via handshaking or touching. This has been proven for almost 200 years, ever since Dr Lister proved that hand washing with antiseptic dramatically cut down on surgical infections (be thankful you didn’t live back then!). Many studies since then have shown decreases in hospital acquired infections with simple hand washing. But people should not waste their money on the trendy anti-microbial soaps with triclosan and other ingredients as they don’t have much evidence of effectiveness, and they likely will lead to a worsening of the already serious worldwide problem of antibiotic resistance. Simple soap and water also does the trick — but I actually prefer the alcohol gels as they work quicker and wipe out a much larger percentage of viruses and bacteria than soap.

Another interesting idea is daily gargling, with simple salt water, during the entire winter season. In a 2005 published study in the American Journal of Preventive Medicine, people who gargled up to three times a day had a 40% decrease in respiratory illness and symptoms during the winter. Gargling also is a simple way to help improve sore throat pain and swelling, and it also loosens up mucus.

And of course, the basics

Don’t forget the obvious concept of a healthy immune system, via exercising, a good diet full of antioxidants, and not smoking!

Don’t Want To Get H7N9 Flu? Get A Good Night’s Sleep!

As this H7N9 infection slowly gains steam, I thought I’d continue to post some quick updates, on top of my previous article mentioning prevention. I wanted to again mention a fascinating 2009 study from the Archives of Internal Medicine which proved that getting less than 7 hours of sleep dramatically increased your risk of getting infection from common viruses. Here’s the abstract:

Background  Sleep quality is thought to be an important predictor of immunity and, in turn, susceptibility to the common cold. This article examines whether sleep duration and efficiency in the weeks preceding viral exposure are associated with cold susceptibility.

Methods  A total of 153 healthy men and women (age range, 21-55 years) volunteered to participate in the study. For 14 consecutive days, they reported their sleep duration and sleep efficiency (percentage of time in bed actually asleep) for the previous night and whether they felt rested. Average scores for each sleep variable were calculated over the 14-day baseline. Subsequently, participants were quarantined, administered nasal drops containing a rhinovirus, and monitored for the development of a clinical cold (infection in the presence of objective signs of illness) on the day before and for 5 days after exposure.

Results  There was a graded association with average sleep duration: participants with less than 7 hours of sleep were 2.94 times (95% confidence interval [CI], 1.18-7.30) more likely to develop a cold than those with 8 hours or more of sleep. The association with sleep efficiency was also graded: participants with less than 92% efficiency were 5.50 times (95% CI, 2.08-14.48) more likely to develop a cold than those with 98% or more efficiency.

This study also was addressed in an article from the New York Times, which offered a less dry summary:

In a recent study for The Archives of Internal Medicine, scientists followed 153 men and women for two weeks, keeping track of their quality and duration of sleep. Then, during a five-day period, they quarantined the subjects and exposed them to cold viruses. Those who slept an average of fewer than seven hours a night, it turned out, were three times as likely to get sick as those who averaged at least eight hours.

Sleep and immunity, it seems, are tightly linked. Studies have found that mammals that require the most sleep also produce greater levels of disease-fighting white blood cells— but not red blood cells, even though both are produced in bone marrow and stem from the same precursor. And researchers at the Max Planck Institute for Evolutionary Anthropology have shown that species that sleep more have greater resistance against pathogens.

The fascinating part is that all test subjects had the rhinovirus dripped into their nose (!), so all were equally exposed — but the sleep deprived got actual cold symptoms 3 times more than the well rested. I think it’s dramatic evidence of the power of our immune system to keep us healthy. So get your sleep!