The Cold Season

It never announces itself. A tickle at the back of the throat on a damp morning, a heaviness behind the eyes, a sneeze that arrives one beat too early. You tell yourself it is the dust, the dry heating, the late night. By the afternoon, you know.

Just a few days ago, it was my turn. And this time I tried something new: a beautiful, locally made honey syrup with pine needles, propolis and lemon. It seemed to work even better than my usual stack of propolis, Biocidin and zinc lozenges. One person's cold is not a clinical trial, of course, and I will come back to that. But it sent me back to a question I ask myself every October. Why does it feel as if everyone around us falls ill at once, just as the leaves turn? And of everything we reach for, from vitamin C to elderberry to chicken soup, what actually holds up?

So I went and checked. What follows is what the research says, what it does not say, and what I will keep in my own cupboard this winter.

Why the Trouble Starts in October

Germs do not take the summer off. Rhinovirus, the most frequent cause of the common cold, is circulating all year, and by Yale estimates roughly one in five of us is carrying it in the nose at any given moment. What changes in mid-autumn is not the virus. It is the stage we have built around it. Three things converge.

We move indoors, and close the windows. A Yale review of the seasonality of respiratory viruses points to two big drivers: the environment and our own behaviour. When cold outdoor air is heated inside our homes, the relative humidity drops to around 20 percent. Dry air carries viral particles more easily, slows the cilia that sweep our airways clean, and, in the Yale lab's work, blunts the immune response too. In rodent experiments, the sweet spot for limiting airborne spread was a relative humidity of 40 to 60 percent. Those are animal data, and the researchers stress that close contact and shared surfaces matter in every season, but they explain why a humidifier and an open window are not just old wives' advice.

We get less light. As the sun drops lower, the skin makes less vitamin D, and the same review lists sunlight and vitamin D status among the factors behind seasonal infections. More on that below.

The nose gets cold. This is the part I find most fascinating. In 2015, a team in Akiko Iwasaki's lab at Yale showed in mouse airway cells that the innate antiviral response to rhinovirus is weaker at 33°C, roughly the temperature inside the nasal passages when we breathe cool air, than at the core body temperature of 37°C. In other words, the cold virus does not simply thrive in a cooler nose. The nose itself defends less well. Then, in 2022, researchers at Mass Eye and Ear in Boston, led by Benjamin Bleier, described a first line of nasal defence I had never heard of: when the nose detects a virus, its cells release billions of tiny decoys called extracellular vesicles into the mucus, which trap the virus before it reaches a cell. In four volunteers exposed to 4.4°C air for 15 minutes, the temperature inside the nose fell by as much as 5°C, and the number of vesicles dropped by nearly 42 percent. The ones that remained carried far fewer virus-binding receptors and about half the antiviral microRNA. Bleier summed it up as losing roughly half of that defence with a small drop in temperature.

A caution, because it matters: this is laboratory work on human nasal tissue and a handful of volunteers, not proof that a chilly walk gives you a cold. An independent rhinologist who reviewed it noted that in vitro findings are often confirmed in living people, but not always. You still need a virus to catch. What the research suggests is that cold tilts the odds. It is also why a scarf pulled up over the nose is less quaint than it sounds.

So what can we do about it? Warm the nose, humidify and air the rooms, and then, the subject of the rest of this piece, make sure the body meeting the virus is as well supplied as it can be.

Vitamin C, the Famous Antioxidant

Vitamin C is the first thing most of us reach for, so it deserves a proper look. For centuries its absence killed sailors. Scurvy, the slow collapse of connective tissue that follows weeks without fresh fruit and vegetables, was the scourge of long sea voyages. In the mid-1700s, the Royal Navy surgeon James Lind determined that citrus fruit could cure it, but nobody knew why. The answer came from a Hungarian biochemist, Albert Szent-Györgyi, who in 1928 isolated a strongly reducing substance from oranges, cabbages and adrenal glands and called it hexuronic acid. In 1932 he and his colleague Joseph Svirbely showed that it protected guinea pigs from scurvy, within weeks of a competing team led by Charles Glen King at the University of Pittsburgh reaching the same conclusion, which sparked a bitter dispute over who deserved the credit. The compound was renamed ascorbic acid, literally the anti-scurvy acid, and its structure was worked out that same year by the British chemist Norman Haworth. Szent-Györgyi won the 1937 Nobel Prize in Physiology or Medicine. His supplies of the stuff kept running out until he realised that Szeged, the Hungarian city where he worked, sat at the heart of the paprika industry. Red peppers turned out to be an extraordinarily rich source.

Humans, unlike most animals, cannot make vitamin C, so we must eat it. And it does a surprising number of jobs: it is needed to build collagen, to make certain neurotransmitters, and to absorb the iron found in plant foods. Its most famous role, though, is as an antioxidant.

What does that actually mean? Our cells burn food for energy, and that process, along with cigarette smoke, air pollution and ultraviolet light, produces free radicals: unstable molecules missing an electron, which grab one from whatever is nearby, including our fats, proteins and DNA. Each theft can set off a chain reaction. An antioxidant is a molecule willing to hand over an electron, so the chain stops. Vitamin C is a generous donor, and it does something else clever: it regenerates other antioxidants, such as vitamin E, after they have done their job. It also accumulates to far higher concentrations inside white blood cells than in the bloodstream, which hints at why immunologists take it seriously.

But "antioxidant" is not a synonym for "more is better." The body regulates vitamin C tightly. Cells appear to be saturated at intakes of around 100 mg a day, and beyond about 200 mg the level in the blood barely rises. Under some conditions vitamin C can even behave as a pro-oxidant. The official recommended intake in the United States is 75 mg for women and 90 mg for men, and five varied servings of fruit and vegetables can supply more than 200 mg. Half a cup of raw red pepper alone gives you about 95 mg, an orange around 70, a kiwi about 64.

So does it prevent colds? For most of us, no. The Cochrane review of 29 trials involving more than 11,000 people found that taking vitamin C every day did not reduce how often ordinary people caught colds. It did, however, shorten them modestly: by 8 percent in adults and 14 percent in children, with 1 to 2 grams a day cutting children's colds by 18 percent. And in five trials of marathon runners, skiers and soldiers on subarctic exercises, people under heavy physical stress and cold exposure halved their risk of catching a cold. Pauling's grand 1970s promise did not survive, but a small, real effect did.

Vitamin C When You Are Already Sick

I had remembered a protocol of one gram an hour for six hours, and I wanted to know where it came from. It is real. It comes from a 1999 paper by two American chiropractors, H. Clay Gorton and Kelly Jarvis, in the Journal of Manipulative and Physiological Therapeutics. Students who reported cold or flu symptoms took 1,000 mg of vitamin C every hour for the first six hours, then three times a day. The authors reported an 85 percent drop in symptom reports compared with the previous year's students, who had been given pain relievers and decongestants.

Before you rush to the pharmacy, look at the design. It was not randomised or blinded, and it compared one year's students with another's. A later critique noted that symptoms were not recorded consistently between the two years. It is an intriguing protocol, not proof.

The better-controlled evidence is more sober. The Cochrane review pooled seven therapeutic comparisons, where vitamin C started after symptoms appeared, and found no consistent effect on duration or severity. An Australian randomised trial of 400 volunteers who took 1 or 3 grams a day at the first sign of a cold, and for two days after, found no difference compared with a token dose. And yet the door has not quite closed. A 2025 review by the Finnish researcher Harri Hemilä, who has spent decades on this question, points to two trials in which 6 to 8 grams a day shortened colds about twice as much as 3 to 4 grams. The Cochrane authors themselves conclude that, given the low cost and good safety record, it may be worthwhile for people to test it on themselves. An hourly gram for six hours adds up to 6 grams, squarely in that range.

If you decide to try it, understand what the body does with it. At doses above 1 gram a day, absorption falls below 50 percent, and what is not absorbed is excreted, or, if you overdo it, draws water into the gut. Diarrhoea, nausea and cramps are the classic limit, often called bowel tolerance. Splitting the doses is the sensible approach. People with a history of kidney stones, or with hemochromatosis, an iron-overload condition, should avoid high doses, and anyone on statins or in cancer treatment should speak to their doctor first.

And the copper? I wanted to include this because I have heard it repeated for years. The truth is a little more nuanced. Ascorbic acid interferes with copper in animal experiments, and some small human studies have seen a dose-related drop in ceruloplasmin, the main copper-carrying enzyme in the blood: one 6-week trial in men found it fell at 1,000 mg a day. But the NIH's fact sheet notes that reported falls in copper and vitamin B12 with high intakes were partly assay artefacts and have not been confirmed by further studies. So the concern is plausible, but not established. The documented downsides of long-term high-dose vitamin C are the better-known ones: gastrointestinal upset, a possible rise in kidney stone risk in susceptible people, and extra iron absorption. The official upper limit is 2,000 mg a day. My own conclusion is a simple one. Get your baseline from food, and keep megadoses for short bursts rather than a daily habit.

Zinc: The Quiet Workhorse

If vitamin C is the celebrity of cold season, zinc is the stagehand. It is needed by hundreds of enzymes, and it plays a role in immune function, wound healing and DNA synthesis. The body holds only about 1.5 grams of it in women and 2.5 grams in men, most of it tucked away in muscle and bone, and it relies on steady intake from food to keep its balance. That is why I think of zinc as a year-round job rather than something to remember when the sniffles arrive. Oysters are the richest source by far (about 32 mg in three ounces), followed by red meat, crab, pumpkin seeds, lentils and dairy. Adults need around 8 mg a day for women and 11 mg for men. People who eat little animal food deserve a second look at their intake, because the phytates in grains and legumes bind zinc and reduce how much we absorb. Soaking beans, grains and seeds, and eating fermented foods, can help.

Then there is the lozenge. The most-quoted number comes from a 2017 meta-analysis by Harri Hemilä at the University of Helsinki, published in JRSM Open. It pooled seven randomised trials of zinc acetate and zinc gluconate lozenges and found that colds were 33 percent shorter on average (95 percent confidence interval 21 to 45 percent). I checked the details, and they matter. The trials used doses above 75 mg of elemental zinc a day; an earlier analysis found that lower doses did not work at all. Trials giving 80 to 92 mg a day did as well as those giving around 200 mg, so more is not better. Zinc acetate averaged a 40 percent reduction and gluconate 28 percent, but the difference could be down to chance. The lozenges should not contain citric acid or citrate, which bind the zinc ions and reduce the effect. And the lozenge has to dissolve slowly in the mouth: the working theory is that zinc ions released in the throat interfere with the rhinovirus attaching to and replicating in the lining of the nose and throat, and calm inflammation. NIH describes this as a hypothesis rather than a proven mechanism.

Now the sobering bit. The most recent Cochrane review, from 2024, pooled 34 trials and concluded that zinc may shorten colds by about two days in people who already have one, but that the certainty of the evidence is low to very low, and that it makes little or no difference to catching a cold in the first place. Taken together, the evidence says: start early, within about a day of the first symptoms, use a proper lozenge, and expect a shorter cold rather than a cure.

And mind the arithmetic. A typical lozenge in the trials contained around 13 mg of zinc and was taken every two to three waking hours, so the total lands far above the 40 mg daily upper limit that applies to everyday intake. That is acceptable for a few days of treatment, but taking 50 mg or more for weeks can interfere with copper absorption, and long-term overuse has been linked to copper deficiency. Zinc can also bind to quinolone and tetracycline antibiotics, so keep them apart. Avoid zinc nasal sprays and gels, which have been linked to a loss of smell.

Vitamin D: Banking the Summer

The instinct to build up vitamin D in summer is sound, as long as it is done without burning. Our skin makes the vitamin when UVB light hits it, and a summer spent outdoors is how most of us fill the tank. The trouble is how quickly it empties. The form measured in a blood test, 25-hydroxyvitamin D, has a half-life of about two weeks, and above roughly 35 degrees latitude the winter sun sits too low for the skin to make meaningful amounts for several months. At Tuscany's latitude, around 43 degrees north, that means something like November through February. In other words, summer's savings do not carry us through the cold season, which is exactly when the research suggests we need vitamin D most.

The best evidence we have is a 2017 individual-participant meta-analysis in the BMJ, led by Adrian Martineau at Queen Mary University of London. It pooled 25 randomised trials and nearly 11,000 people and found that vitamin D supplementation reduced the risk of an acute respiratory infection by about 12 percent overall (adjusted odds ratio 0.88). The detail is where it gets interesting. The benefit came from daily or weekly doses, with a risk reduction of about 19 percent, and it was strongest in people who started out very deficient, below 25 nmol/L, where the odds fell by 70 percent. People who got occasional large bolus doses saw no protection at all.

That last finding bears on something I had assumed: that taking a larger dose at the first sign of illness might help. I went looking for good evidence and did not find any. What the trials support is steady daily intake, particularly if your levels are low, rather than a rescue dose. A more recent trial, CORONAVIT, offered 6,200 UK adults a vitamin D test and then 800 or 3,200 IU a day for six months. Neither dose reduced all-cause respiratory infections or covid compared with no offer, and a few people on the higher dose developed hypercalcaemia that resolved once they stopped. The two results are not contradictory. Vitamin D appears to help the people who are truly short of it, and to do little for those who are already topped up. That is a strong argument for knowing your own level.

So my approach is simple. Get some sun when it is available, get a blood test (the 25-hydroxyvitamin D test) before and after winter, and supplement daily through the dark months at a dose guided by the result. The upper intake level for adults is 4,000 IU a day, and exceeding it for long periods can cause calcium to build up in the blood. Vitamin D works hand in hand with other nutrients, which is one more reason to think of it as part of a pattern rather than a pill.

Nasal Sprays: Guarding the Front Door

Given that the nose is where most cold viruses first land, and where, as we saw, the cold weakens our defences, it makes sense to protect it directly. Nasal sprays that claim to block viruses are now everywhere, so I wanted to look at what has actually been tested.

Xlear, the one I had in mind, combines 11 percent xylitol, 0.2 percent grapefruit seed extract and saline. The manufacturer's science page and press releases point to laboratory studies in which the spray reduced SARS-CoV-2 in a test tube after about 25 minutes of contact, and to a small case series of COVID patients. The proposed mechanism is that the xylitol stops viruses from sticking to the cells while the grapefruit seed extract inactivates them. That is a reasonable hypothesis, but I could not find a randomised trial of Xlear in common colds, and the in vitro work is largely company-promoted, not independent confirmation. It may well be useful as a moist, gentle nasal rinse. I would not tell you it has been shown to stop a cold.

The better-evidenced option is a different one: iota-carrageenan, a polymer extracted from red seaweed that appears to bind to viruses and keep them from attaching to the cells of the nose. A pooled analysis of two randomised, placebo-controlled trials in people with virus-confirmed colds found that those using the spray recovered nearly two days sooner, with fewer relapses. The picture is not entirely clean, though. A later, 200-person trial of the same spray, the ICICC trial, missed its main target; the symptom difference did not reach statistical significance, although exploratory analyses favoured the spray. The trials were small, and the studies were backed by the companies that developed and licensed the product. Even the saline placebo may have helped.

My takeaway is a modest one. A nasal spray used early is low-risk and plausible, and the carrageenan sprays have the stronger trial record. But as with every product in this piece, the question to ask is who ran the study, and whether the claim on the box matches what was actually measured. Avoid zinc-containing nasal sprays and gels, for the reason I mentioned above.

Propolis: The Hive's Own Antiseptic

I had always heard that bees embalm their dead, and I wanted to see whether it was true. It is, and it is one of the most vivid pieces of natural history I came across while writing this. In winter, mice sometimes squeeze into beehives for the warmth. While the bees cluster around the brood in the centre, the corners of the hive go undefended. If a mouse dies there, the bees face a problem: it is far too big for them to carry out, as they would a dead bee. Their solution is to coat the carcass in propolis, layer by layer, sealing it off so that it cannot rot and spread disease. Entomologists at Mississippi State describe it as mummification. A review in the journal Apidologie even shows a mouse skull found encased in propolis in a University of Minnesota apiary, and a beekeeper's journal has documented an experiment in which bees entombed dead mice placed on the floor of a colony. The same propolis lines the inner walls of the hive, a so-called propolis envelope, which researchers consider part of the colony's collective immune system.

Propolis itself is made of plant resins that bees gather from trees, chew, and mix with wax and saliva. It is sticky and pliable in warm weather and hard and brittle when cold. Its chemistry is rich and varies by region and season: more than 300 compounds have been identified, with flavonoids and phenolic acids doing much of the work.

In the laboratory, propolis shows antibacterial, antiviral and anti-inflammatory activity, which is what makes it so attractive for sore throats and colds. In people, the picture is less settled. A 2022 review of its antiviral and immune effects concluded that the preclinical evidence is promising, but that rigorous randomised trials in respiratory disease are still lacking. Another review found few adverse effects, with contact allergy the main one. So if you have asthma or a known allergy to bee products, be careful. Quality also varies enormously from one product to another, and I would favour a single-origin propolis from a beekeeper you can identify over an anonymous extract.

In short, propolis has a fascinating biology and a plausible case for throat comfort and antimicrobial activity, though it falls short of clinical proof for colds. That is why I think of it as one tool among several, not a magic bullet.

Honey, and the Syrup That Surprised Me

Honey is one of the few folk remedies that has been through proper trials, and it comes out rather well. A Cochrane review of six randomised trials, covering 899 children aged one to sixteen with coughs from upper respiratory infections, concluded that honey probably relieves cough, and its effect on sleep, better than no treatment, and that it did as well as the common cough-medicine ingredient dextromethorphan. The reviewers were careful: most children received honey for a single night, and the benefits are likely small. But when conventional medicine has so little to offer for a cough, a spoonful of something safe and delicious that coats the throat is a reasonable first move. One rule is not negotiable, and you already know it: no honey for babies under twelve months, because of the risk of infant botulism.

What about "local"? What "local" can genuinely give you is traceability, and that matters more than it should. In a 2023 European Commission investigation called "From the Hives", 147 of 320 samples of imported honey, 46 percent, were suspected of being adulterated with cheap syrups made from rice, wheat or sugar beet. The testing methods had changed since an earlier round that flagged 14 percent, so the numbers are not strictly comparable, and they concern imports rather than all honey. Still, the lesson is the one we know from olive oil: a beekeeper whose name is on the jar is the best guarantee of what is inside it.

And my syrup. A few days ago I tried, for the first time, a local honey syrup made with pine needles, propolis and lemon. It was lovely: resinous, warming and soothing, and I felt it did better for me than my usual stack. I should be honest about what that proves. In a carrageenan nasal spray trial I read, colds lasted about seven and a half days on average whether people received the active spray or the placebo. One person's cold is simply not evidence. What I can say is that each ingredient has something going for it: honey soothes, lemon adds a little vitamin C, propolis has its biology, and pine needles are a traditional winter tonic, usually described as rich in vitamin C, though I found no rigorous measurements. If you make your own, identify the tree with certainty. Yew is highly toxic, ponderosa pine is best avoided, and pregnant women are generally advised to skip pine needle preparations altogether. And a ritual that makes you feel looked after is not nothing.

Elderberry: Dark Purple and Worth a Closer Look

I will confess to a soft spot for elderberry. The black elder, Sambucus nigra, is a hedgerow tree across Europe, and its deep purple berries have been brewed into winter syrups for centuries. The question is whether the habit rests on anything more than tradition, and the answer is: a little, with caveats.

A 2019 meta-analysis of four small randomised trials, 180 people in all, found that elderberry reduced upper respiratory symptoms in colds and flu. The most-cited single study is a 2016 trial of 312 long-haul air travellers from Australia, who took 600 to 900 mg a day of a standardised extract before, during and after their trip. Those who caught a cold had shorter and milder colds on elderberry than on placebo. Now the caveats. Three of the four pooled trials were industry-funded, and the most independent one, a 2020 emergency-department trial of 87 people over the age of five with lab-confirmed influenza, found no benefit from five days of extract. Reviewers rate the overall certainty as low. My honest summary is that there is a plausible, modest signal, not a proven effect.

A safety note that matters. Raw or unripe berries, and the leaves, stems and seeds, contain cyanide-releasing compounds that can cause vomiting and diarrhoea, and a 1984 CDC report described poisoning from juice made with uncooked berries. Cooking neutralises them, which is why commercial syrups are considered safe and why I would not improvise with berries picked from a hedge and eaten raw. Data in pregnancy and breastfeeding are too thin to judge, and the data in young children are thin too: a few liquid extracts have been used for up to five days in children aged five to twelve without problems, but nobody has tested a whole season in a toddler. I gave an elderberry elixir to my son when he was a toddler, and I would suggest any parent check with their paediatrician first.

How to tell a real extract from sugar syrup in a pretty bottle. This is my own checklist, built on label logic rather than on a trial:

• The species and the amount. Look for Sambucus nigra, the species used in most trials, and for a stated amount of elderberry per dose or a percentage. A label that says only "elderberry flavour" or lists the berry as an afterthought is a sugar syrup.
• The first ingredient. If glucose or fructose syrup, or plain sugar, leads the list, you are buying a sweet syrup with a hint of elderberry. Honey, a small amount of sugar, or none at all is better.
• Cooked, not raw. Reputable products use cooked berries or standardised extracts.
• A dose that resembles the trials. The air-traveller study used 600 to 900 mg a day of extract. Gummies in particular rarely come close.
• A maker you can identify. Small-batch, organic producers who name their ingredients are easier to trust, and they are often found at farmers' markets and organic shops rather than on supermarket shelves.

One of my favourites has long been the Elderberry Elixir by Sweet Bee Organics, a UK maker. Its label is the kind I look for: water, honey, elderberries at a declared 8.3 percent, ginger, cinnamon, turmeric, rosemary, cloves, a little cognac, and added vitamin C. A word for parents: it contains honey, so it is not for under-ones, and the cognac is worth knowing about.

Cod Liver Oil: A Spoonful of Tradition

Cod liver oil is one of my personal favourites in the winter kitchen, and not because it is a cold remedy. It is one of the few foods that is a natural source of three nutrients that matter in winter at once: vitamin A, vitamin D and the long-chain omega-3 fats EPA and DHA. Scandinavian families have given it to children through the dark months for generations. The brand I trust, and the only one I feel comfortable recommending, is Rosita. Its maker describes an extra virgin oil from wild-caught Norwegian cod, extracted without heat, with no synthetic vitamins added. Those are the company's claims, so treat them as such, but the label is refreshingly specific: per teaspoon, roughly 1,100 micrograms of vitamin A, about 9 to 10 micrograms (360 to 400 IU) of vitamin D, and around a gram of EPA and DHA combined, with the maker noting some variation from batch to batch.

Now the honest part. The best test of the idea, a Norwegian trial published in the BMJ in 2022, gave 34,601 adults 5 ml of cod liver oil or a corn-oil placebo daily through the winter of 2020 to 2021. Cod liver oil did not reduce respiratory infections: 22.9 percent reported at least one in the cod liver oil group against 22.1 percent in the placebo group. Two points soften that result. Most participants were young, healthy and already had adequate vitamin D, and the study was funded by the maker of the oil used. That fits what we saw with vitamin D: supplements seem to help people who are short of a nutrient, and do little for people who are not. So I would not take cod liver oil to ward off a cold. I would take it as a nutrient-dense whole food in a diet that is otherwise low in oily fish, and perhaps as a way to cover the vitamin D gap between November and March.

More is not better. Cod liver oil carries preformed vitamin A, or retinol, which the liver stores. The upper limit for adults is 3,000 micrograms a day, from all sources combined. A teaspoon of Rosita lists about a third of that, so add a multivitamin and a plate of liver pâté and you can approach the ceiling without trying. Long-term excess can damage the liver, and high doses of preformed vitamin A are linked to birth defects, which is why UK health advice tells pregnant women to avoid supplements containing vitamin A, fish liver oil included, unless their GP says otherwise. Stick to the dose on the label, check the vitamin A in everything else you take, and do not double up because you feel a cold coming.

One practical tip: an oil this fresh is delicate. The maker recommends keeping it refrigerated and finishing a bottle within about three months of opening. If it smells sharp or rancid, throw it out.

In the Kitchen: Where Most of the Work Gets Done

For all the bottles and lozenges, the most reliable cold-season strategy lives in the kitchen, and it is the least glamorous.

Vitamin C, the food way. You do not need a supplement to reach the amounts we discussed. According to NIH figures, half a cup of raw red pepper gives you about 95 mg, an orange about 70, a medium kiwi about 64, half a cup of sliced strawberries about 49, and a half cup of cooked Brussels sprouts about 48. Five varied servings of fruit and vegetables a day can supply more than 200 mg. Vitamin C is water-soluble and fragile in heat, so eat some of it raw, and steam or microwave the rest, not boil it into oblivion.

The gut and the immune system. You will often hear that about 70 percent of the immune system lives in the gut. The figure is repeated everywhere and its origin is hard to pin down, so I would treat it as a rough estimate. The underlying point is solid, though: the gut wall is home to a large share of the body's immune tissue, and it is in constant conversation with the bacteria that live there. Prebiotic fibre, the food those bacteria like best, comes from onions, garlic, leeks, oats, legumes and the like. Fermented foods such as yoghurt, kefir, sauerkraut and kimchi provide live bacteria, and NIH notes that the organic acids in fermented foods may also help the body absorb zinc. As for probiotic supplements, a Cochrane review updated in 2022, covering 23 trials, concluded that probiotics were better than placebo in preventing acute upper respiratory infections. The strains, doses and quality of the studies varied widely, so I see it as encouraging rather than conclusive, and I would not buy a particular brand on the strength of it.

Chicken soup, the oldest remedy. Every culture has its own version and none of them waited for a trial, but there are two. In 1978, researchers at Mount Sinai in Miami Beach measured how fast mucus moved through the noses of 15 healthy volunteers after they drank different liquids. Hot water by sip and hot chicken soup by sip both sped it up, the soup a little more, which the authors attributed partly to inhaled steam and partly to something in the soup's aroma or taste. The effect faded within 30 minutes, while cold water actually slowed mucus down. Then, in 2000, Stephen Rennard at the University of Nebraska tested his wife's family recipe in the laboratory and found that it slowed the migration of neutrophils, white blood cells that drive inflammation, hinting at a mild anti-inflammatory effect. That was a test-tube result, not a cure. Chicken soup will not shorten your cold. It will hydrate you, soothe your throat, clear your nose for a little while, and make you feel looked after, which on day two of a cold is no small thing.

Once You Are Ill: Fluids, Appetite and an Old Saying

Everyone tells you to drink plenty when you are ill, and it is sound common sense, but it is worth knowing how little has been formally tested. A Cochrane review looking for randomised trials of advising people with respiratory infections to drink more found none, so there is no trial evidence for or against it, and the authors noted theoretical reasons why forcing fluids might do harm in some situations. A sensible reading is to drink to thirst, a little more when you have a fever, and more still if you are losing fluid through sweating, vomiting or diarrhoea. In those cases, plain water is not enough, because you also lose salts. Broth, a pinch of salt in a drink, or an oral rehydration solution from the pharmacy does a better job than a litre of water on its own.

"Feed a cold, starve a fever." The saying is old. The English phrase is usually traced to a sixteenth-century dictionary by John Withals, which includes the line "Fasting is a great remedie of feuer". For most of the intervening centuries it was folklore, but two pieces of modern research have given it an unexpected twist. A small human study from 2002 found that eating was followed by a rise in interferon gamma, an immune signal used against viruses, while fasting was followed by a rise in interleukin 4, which is more involved in the response to bacteria. Then, in 2016, Ruslan Medzhitov's team at Yale infected mice with either a flu virus or a bacterium. Force-feeding protected the virus-infected mice but harmed those with the bacterial infection, and the culprit turned out to be glucose: viruses seemed to need it, while bacterial infections were better tolerated when the body ran on ketones, the fuel made during fasting. In other words, the old rhyme may have been closer to "feed a virus, starve a bacterium".

Before we rewrite grandmother's wisdom, a few cautions. These were mice, of a single strain, with two infections, and the authors themselves say we should not take the adage literally. A fever is not a diagnosis, and you cannot tell which kind of germ you have from the sofa. The practical conclusion is a gentle one: let your appetite lead. If you are hungry, eat something nourishing, such as soup, eggs or porridge. If you are not, do not force it, and make sure that you drink. And if a fever lasts more than a few days, or you feel much worse instead of better, see a doctor, because a bacterial infection may need treatment that no syrup can provide.

The Evidence at a Glance

Nothing here is a cure. A few things have a modest, believable effect, and many have an appealing story and little trial evidence. This is where each remedy stands.

Questions You Will Probably Ask

Letting the Body Do Its Work

If there is one thread running through everything I read for this piece, it is that the most powerful intervention happens long before the first sniffle. The evidence for almost every remedy here says the same thing in different words: supplements help most when you are short of something, and do little when you are not. Vitamin D works best for the deficient, zinc matters most for those who eat little of it, and vitamin C shines under stress. The surest way to be on the right side of that line is to be well nourished most of the time, with real food, enough protein, colourful vegetables, oily fish, some sun in the summer, and a measured dose of what winter takes away. Do that, and when illness does arrive, as it will, it is more likely to be shorter and gentler.

And when it does arrive, the most underrated remedy is the one that costs nothing. Cancel what you can. Warm the room, and keep your nose warm outside. Make the soup, or heat the broth, and have a spoonful of the good honey. Take what you trust from the cupboard, in sensible amounts. Then get under a blanket, put on a film you have seen ten times, and let your white blood cells get on with a job they have been doing, quietly and rather brilliantly, for a very long time.

Sources

Gina Sakic Editor-in-Chief of GlamBon. Born in Croatia and educated in Italy and Australia, with a career spanning the Melbourne International Film Festival, corporate video production and functional nutrition. Now based in Tuscany, she writes at the intersection of culture, health and sustainability.