If you want to know how to avoid getting sick this winter, the honest ranking is: wash your hands, sleep more than seven hours, get vaccinated, and improve the air in the rooms you spend the most time in. Those four have the strongest evidence behind them by a wide margin. Almost everything sold in the immunity aisle — vitamin C megadoses, echinacea, elderberry — has weak or null evidence for preventing infection, and we’re going to be specific about which is which.
By Priya Shetty, MS, RD — Wellness Editor, The Culture Mom | Registered dietitian, MS in nutritional sciences, 9 years in clinical and community nutrition
Published August 12, 2026. Editorially reviewed by Holly Rosen Fink, Editor-at-Large.
Priya Shetty is a registered dietitian, not a physician. This article is general nutrition and health information, not medical advice. Talk to your doctor before starting any supplement, especially if you’re pregnant, nursing, immunocompromised, or taking prescription medication.
Key takeaways
- Handwashing has the strongest, most consistent evidence of any single behavior. The CDC estimates that handwashing reduces respiratory illnesses like colds in the general population by 16 to 21 percent.
- Sleep is the most underrated variable. In a controlled rhinovirus challenge study, adults sleeping under 6 hours a night were roughly 4.2 times more likely to develop a cold than those sleeping more than 7 hours.
- Vitamin C megadoses do not prevent colds in the general population. A Cochrane review of 29 trials and over 11,000 people found no reduction in how often people got sick; regular supplementation shortened colds by about 8 percent in adults, which is a few hours.
- Zinc lozenges have the most defensible case among supplements, but only for shortening a cold that’s already started, only if begun within about 24 hours of symptoms, and only in specific forms and doses. Nasal zinc products have been linked to permanent loss of smell and should be avoided.
- Vitamin D supplementation appears to help people who are actually deficient and does little for people who aren’t. Get a level tested before you supplement rather than guessing.
What actually reduces your risk of getting sick?
Four things: handwashing, adequate sleep, vaccination, and better indoor air. Everything else on this page is a smaller effect, a conditional effect, or a marketing claim.
Here’s the honest hierarchy as we read the evidence:
| Intervention | Strength of evidence | Roughly what it does | Cost |
|---|---|---|---|
| Handwashing with soap | Strong | 16–21% fewer respiratory illnesses (CDC estimate) | Near zero |
| 7+ hours of sleep | Strong (experimental) | ~4x lower odds of developing a cold vs. under 6 hours | Free, hard |
| Annual flu vaccine | Strong | 40–60% reduction in flu illness in well-matched seasons | Usually $0 with insurance |
| Updated COVID vaccine | Strong | Meaningful reduction in symptomatic infection and hospitalization | Usually $0 with insurance |
| Ventilation / air changes | Moderate to strong | Lowers airborne viral concentration indoors | $0 (open a window) to $300 |
| Masking in crowded indoor settings | Moderate | Reduces exposure; effect depends heavily on fit and consistency | ~$1 per N95 |
| Correcting vitamin D deficiency | Moderate, conditional | Helps if deficient; little effect if replete | $10–$20/yr + a lab test |
| Zinc lozenges within 24h | Low to moderate, for duration only | May shorten a cold; does not prevent one | $8–$15 per course |
| Vitamin C megadoses | Null for prevention | No reduction in incidence; ~8% shorter colds in adults | $10–$30/yr |
| Echinacea | Weak / inconsistent | No reliable preventive effect | $15–$30 |
| Elderberry | Weak / insufficient | Not established | $15–$40 |
The pattern is worth naming: the interventions with the best evidence are boring, cheap, and behavioral, and the ones with the worst evidence are the ones with a product attached. That’s not a coincidence.
Does handwashing really reduce how often you get sick?
Yes — it’s the single best-supported thing on this list. The CDC’s clean hands guidance puts the effect at a 16 to 21 percent reduction in respiratory illnesses like colds across the general population, and a 23 to 40 percent reduction in diarrheal illness.
That effect size sounds modest until you multiply it across a household with school-age kids and a full winter. One in five colds avoided, across four or five people, over five months, is a meaningfully different season.
What matters technically:
Time, not temperature. Twenty seconds of scrubbing with soap. Water temperature has no meaningful effect on pathogen removal at any temperature a person can tolerate.
Cover the parts people skip. Backs of hands, between fingers, under nails, and thumbs. Thumbs are the most commonly missed surface.
Alcohol-based sanitizer is a good substitute, not a replacement. At 60 percent alcohol or higher it works well on most respiratory viruses, but it doesn’t remove visible soil, and it’s notably less effective against norovirus — the winter stomach bug that circulates alongside colds and flu.
The highest-yield moments are after coming home, before eating, after using a shared bathroom, and after handling shared surfaces in a school or office. Handwashing on arrival home is the single habit we’d install first, especially for kids.
The other physical measure worth doing: don’t touch your face. It’s nearly impossible to do consistently, which is exactly why handwashing is the intervention that works — it addresses the hands, not the impulse.
How much does sleep affect your chance of catching a cold?
More than almost anything else you can control, and the evidence here is unusually strong because it comes from a controlled challenge study rather than self-report. In Prather et al., published in Sleep in 2015, 164 healthy adults wore actigraphy monitors for a week, were then given nasal drops containing rhinovirus, and were quarantined and monitored for five days.
The result: participants who had been sleeping less than 6 hours a night were about 4.2 times more likely to develop a cold than those sleeping more than 7 hours. Those sleeping under 5 hours were 4.5 times more likely. The effect held after controlling for age, BMI, season, smoking, income, education, stress, and pre-existing antibody levels.
Four times. That’s a larger effect than any supplement on this page produces, and it’s free.
The practical read for parents, who are the people most likely to be running a sleep deficit in December: protecting sleep is a legitimate infection-control strategy, not a self-care indulgence. If you have to choose between a 45-minute wind-down routine and an extra 45 minutes of sleep, take the sleep.
The specifics that help most:
- A consistent wake time matters more than a consistent bedtime for total sleep quality.
- Alcohol reduces sleep quality even when it makes you fall asleep faster — a relevant tradeoff during a holiday season built around evening drinking.
- If you’re chronically under 6 hours because of a newborn, a job, or both, the goal isn’t perfection. Getting from 5.5 to 6.5 hours is where a lot of the curve lives.
We’ve written more on making this practical in sleep schedules for working moms.
Do flu and COVID vaccines actually reduce your chance of getting sick?
Yes, though not to zero, and the honest framing matters here. The CDC’s flu vaccine effectiveness studies show that in seasons when the vaccine is well matched to circulating strains, vaccination reduces the risk of flu illness by roughly 40 to 60 percent among the overall population.
Forty to sixty percent is not 100 percent, and people who get flu after a flu shot understandably conclude the shot failed. The more accurate reading is that vaccination substantially reduces both the odds of getting sick and, if you do get sick, the odds of a severe outcome or hospitalization. Both effects are real; the second is the one that matters most for older adults, pregnant people, and anyone with chronic lung or heart conditions.
Practical points:
- Timing: for flu, September or October in most of the U.S., so protection is high through the winter peak. Getting one in December is still worth doing.
- Kids under 9 getting a flu vaccine for the first time need two doses, four weeks apart. This is the detail most often missed.
- You can get flu and COVID vaccines at the same visit. CDC guidance permits co-administration.
- RSV vaccines and immunization now exist for older adults, for pregnant people in a specific window, and for infants via monoclonal antibody. Ask your doctor or your pediatrician whether you or your child is in an eligible group.
Which vaccines you personally should get is a conversation for your physician, not a decision to make from an article. Bring your age, pregnancy status, and any chronic conditions to that conversation.
Does ventilation actually matter indoors?
Yes, and it’s the most overlooked of the four high-evidence measures. Respiratory viruses transmit in large part through the air, and the concentration of virus in a room is a direct function of how much fresh or filtered air moves through it.
The CDC’s building ventilation guidance recommends targeting at least 5 air changes per hour in occupied spaces as a baseline for reducing airborne disease transmission. The EPA’s indoor air quality guidance points to the same set of levers: increase outdoor air, improve filtration, and use portable air cleaners where central systems can’t do the job.
At home, that translates to three things:
Open a window, even briefly. Ten minutes of cross-ventilation in a room where someone is sick moves more air than most people assume. Cold weather is the reason nobody does this and also the reason it matters most.
Upgrade your furnace filter. A MERV 13 filter, if your system can handle the pressure drop, filters a meaningful fraction of respiratory aerosols. Check your system’s specifications first — pushing a too-restrictive filter into an undersized blower reduces airflow and can make things worse.
Run a portable HEPA air cleaner in the room where people sleep or gather. Size it to the room using its CADR rating, not its marketing claims. We go through how to do that math in our guide to the best air purifiers for home.
The winter version of this that people resist: a household where one person has flu should not be a sealed box. Isolate the sick person in one room, crack a window in that room, and run an air cleaner in it.
Does vitamin C prevent colds?
No — not in the general population, and we’d rather say that plainly than hedge. The evidence here is unusually clear. The Cochrane review of vitamin C for preventing and treating the common cold pooled 29 trials with more than 11,000 participants and found that regular vitamin C supplementation produced no reduction in the number of colds people got in community populations.
What it did find:
- Regular supplementation of 200 mg/day or more shortened cold duration by about 8 percent in adults and 14 percent in children. On a 7-day cold, 8 percent is roughly half a day — and that’s for people taking it every day, before getting sick, not starting it once symptoms appear.
- Trials that started vitamin C after symptoms began showed no consistent benefit.
- There is one real exception: in five trials of people under extreme short-term physical stress — marathon runners, skiers, soldiers on subarctic exercises — vitamin C roughly halved cold incidence. Unless you’re doing that, the finding doesn’t apply to you.
So the 1,000 mg effervescent tablet you take at the first tickle in your throat is not doing what the packaging implies. Vitamin C is water-soluble and cheap, the risk is low, and if it’s part of your routine there’s no harm in continuing at reasonable doses — but taking megadoses of it is not a prevention strategy. Very high doses (above roughly 2,000 mg/day, the tolerable upper intake level for adults) mostly produce GI upset and, in susceptible people, raise kidney stone risk.
Get vitamin C from food, where it comes with everything else in the produce. One red bell pepper has more than an orange.
Do zinc lozenges shorten a cold?
Possibly — this is the supplement with the most defensible case, but the conditions are narrow and the evidence is lower-certainty than most marketing suggests. Zinc lozenges may shorten cold duration if started within about 24 hours of the first symptom, in the right chemical form, at a high enough total daily dose.
The specifics that trials generally use:
- Form: zinc acetate or zinc gluconate lozenges, dissolved slowly in the mouth. Zinc bound to citrate, tartrate, or mannitol/sorbitol in some formulations doesn’t release ionic zinc effectively.
- Dose: the positive trials typically use total daily zinc in the range of 75 mg or more, split across lozenges through the day.
- Timing: within 24 hours. Starting on day three doesn’t reproduce the effect.
- Duration: only for the length of the cold. This is not a daily supplement.
What zinc does not do is prevent you from getting sick in the first place — the prevention evidence is weak.
Two cautions worth stating clearly. First, high-dose zinc taken continuously for weeks can interfere with copper absorption and cause a real deficiency; it’s a short-course intervention, not a winter-long habit. Second, avoid intranasal zinc products entirely. The FDA advised consumers to stop using zinc gluconate nasal gels and swabs after more than 130 reports of anosmia — loss of the sense of smell — some of it long-lasting or permanent. That risk is not worth a shorter cold.
Zinc lozenges also taste unpleasant and cause nausea in a meaningful share of people. That’s a real reason many trials had dropouts, and a real reason you may not finish a course.
What about echinacea and elderberry?
Both are oversold. Echinacea has been studied a great deal and the results don’t hold together; elderberry has been studied much less than its shelf space implies.
Echinacea. The Cochrane review of echinacea for preventing and treating the common cold concluded that echinacea products have not shown a reliable preventive benefit, and that any treatment effect on duration is small and inconsistent across preparations. Part of the problem is that “echinacea” isn’t one thing — different species, different plant parts, and different extraction methods produce products that aren’t comparable to each other. A trial showing a small benefit for one preparation says nothing about the bottle on your shelf.
Elderberry. The NIH National Center for Complementary and Integrative Health’s elderberry page is direct: there isn’t enough evidence to determine whether elderberry helps with colds or flu. The studies that exist are small, often industry-funded, and use varying preparations. Raw or unripe elderberries, leaves, and stems also contain compounds that can cause nausea and vomiting — commercial syrups are processed, but homemade preparations are a real risk.
Our position: if you enjoy elderberry syrup and it’s within your budget, it’s unlikely to hurt you. But it should not displace a flu shot, and it should not be described to your kids as the thing keeping them well. Neither of these is a reason to skip anything with better evidence.
What does vitamin D actually do for immunity?
Vitamin D appears to reduce respiratory infection risk in people who are genuinely deficient, and to do very little in people whose levels are already adequate. That conditional finding is the whole story, and it’s why blanket “take vitamin D for immunity” advice is wrong in both directions.
Meta-analyses of randomized trials have found a modest protective effect against acute respiratory infection overall, with the benefit concentrated in participants with low baseline levels and in trials using daily or weekly dosing rather than large infrequent bolus doses. Large trials in already-replete populations — including the VITAL trial’s respiratory infection analyses — have not shown a meaningful benefit.
What to do with that:
Get tested rather than guessing. A serum 25-hydroxyvitamin D test is inexpensive and usually covered. Your doctor can tell you whether you’re deficient and what dose is appropriate.
Know if you’re higher risk for deficiency. People with darker skin, people who cover for religious reasons, people living at northern latitudes, older adults, people with malabsorption conditions, and people who are rarely outdoors all have higher rates.
Don’t megadose. The NIH Office of Dietary Supplements vitamin D fact sheet sets the tolerable upper intake level at 4,000 IU/day for adults. Toxicity is real, and it’s a hypercalcemia problem, not a hypothetical one.
If your doctor does recommend supplementing, our roundup of the best vitamin D supplements covers form, dose, and third-party testing.
What should you eat during cold and flu season?
Eat enough total food, enough protein, and a wide range of plants — that’s the honest nutrition answer, and it’s less exciting than the immunity-boosting framing. As a dietitian, I want to be careful here: no food “boosts” immunity in the sense the marketing implies, and an over-active immune response isn’t a goal anyway. What nutrition does is support normal immune function, and deficiencies impair it.
What genuinely matters:
Protein. Antibodies and immune cells are built from amino acids. Under-eating protein is one of the more common and more consequential gaps, particularly in older adults and people restricting calories. Aim for a protein source at every meal.
Total energy. Chronic under-eating impairs immune function. This is the part most often left out of winter wellness content.
Zinc, vitamin A, vitamin C, selenium, iron, and vitamin D from food. Deficiencies in each of these impair specific immune functions. Getting them from food — meat, seafood, eggs, dairy, legumes, nuts, seeds, and a variety of vegetables — is more reliable than supplementing one in isolation.
Fiber and fermented foods. A large share of immune tissue sits in the gut, and dietary fiber and fermented foods shape the gut environment. The evidence is more promising than proven, but the recommendation carries essentially no downside. We cover the practical version in how to improve gut health.
Fluids. Not because hydration prevents infection, but because being adequately hydrated makes symptoms more tolerable and thins secretions.
What doesn’t matter as much as the internet claims: “detox” teas, celery juice, ultra-high-dose single-nutrient supplements, and anything marketed as alkalizing. And a note on the classic: chicken soup is genuinely a good thing to eat when sick — it’s fluid, sodium, protein, and warm steam — but that’s mechanism, not medicine.
Is it a cold, the flu, COVID, strep, or RSV?
Colds come on gradually and stay above the neck; flu comes on suddenly with fever and body aches; COVID overlaps heavily with both and needs a test to distinguish; strep is a sore throat without a cough; and RSV is most dangerous in infants and older adults. Here’s how they typically separate:
| Illness | Onset | Fever | Hallmark features | What to do |
|---|---|---|---|---|
| Common cold | Gradual, 1–3 days | Rare or low | Runny nose, sneezing, mild sore throat, cough | Supportive care; usually 7–10 days |
| Influenza | Abrupt, hours | Usually, often high | Body aches, headache, exhaustion, dry cough | Call your doctor within 48h — antivirals work best early |
| COVID-19 | Variable | Sometimes | Overlaps everything; sometimes loss of taste/smell | Test. Antivirals exist for higher-risk people |
| Strep throat | Rapid | Often | Severe sore throat, swollen tonsils, no cough, swollen neck nodes | Needs a rapid test or culture; requires antibiotics |
| RSV | Gradual | Sometimes | Wheezing, congestion; serious in infants and adults 60+ | Watch breathing closely in infants; call the pediatrician |
| Norovirus | Abrupt, 12–48h after exposure | Sometimes low | Vomiting and diarrhea, no respiratory symptoms | Hydration; sanitizer doesn’t kill it — wash hands |
The two distinctions that change what you should do: a cough usually rules against strep (per CDC guidance on group A strep, cough and runny nose point away from strep and toward a virus), and flu antivirals need to be started within about 48 hours to do much good. If you have an abrupt high fever plus body aches, that’s a same-day phone call, not a wait-and-see.
Only a clinician can actually make these diagnoses. This table is for deciding whether to call, not for deciding what you have.
When should you call a doctor?
Call immediately for trouble breathing, chest pain, confusion, dehydration, a fever that returns after improving, or symptoms lasting beyond about 10 days without improvement. Those are the general adult red flags, and they apply regardless of what you think you have.
Call sooner and with a lower threshold if you or your child is in a higher-risk group: infants under 6 months, adults over 65, pregnant people, and anyone with asthma, diabetes, heart disease, chronic lung disease, or a condition or medication that suppresses the immune system.
Specific reasons to call the same day:
- Any fever in an infant under 3 months. This is an emergency-department conversation, not a wait.
- Working to breathe in a child — flaring nostrils, pulling in between the ribs, grunting, or a rate that seems fast at rest.
- Signs of dehydration — no wet diaper in 8 hours, no tears, dry mouth, lethargy.
- Sore throat with fever and no cough, which warrants a strep test.
- Abrupt onset of fever and body aches in flu season, especially if you’re in a higher-risk group, because antivirals are time-sensitive.
- Symptoms that improve and then get worse. A “second fever” after a few good days is one of the more reliable signals of a secondary bacterial infection.
Again: I’m a dietitian. Nothing here replaces an actual clinical assessment, and if you’re weighing whether to call, call. The rest of our evidence-based health coverage is in Wellness, and you can read about our editorial standards and who reviews this work on our editors page.
Frequently asked questions
What is the best way to avoid getting sick in winter?
Wash your hands with soap for 20 seconds, sleep more than seven hours a night, get your flu and updated COVID vaccines, and improve ventilation in the rooms you use most. Those four have the strongest evidence by a wide margin. Handwashing alone is estimated by the CDC to cut respiratory illnesses in the general population by 16 to 21 percent.
Does vitamin C prevent colds?
No. A Cochrane review of 29 trials and more than 11,000 people found regular vitamin C supplementation did not reduce how often people in the general population caught colds. It shortened cold duration by roughly 8 percent in adults and 14 percent in children, and only when taken daily beforehand. Starting a megadose once symptoms appear shows no consistent benefit.
Do zinc lozenges actually work for colds?
They may shorten a cold, but only if started within about 24 hours of the first symptom, using zinc acetate or gluconate lozenges at total daily doses around 75 mg or more. They do not prevent colds. Do not use intranasal zinc products — the FDA warned about them after more than 130 reports of lost sense of smell.
How much does sleep affect getting sick?
A great deal. In a controlled study where 164 healthy adults were exposed to rhinovirus after a week of monitored sleep, those averaging under 6 hours a night were about 4.2 times more likely to develop a cold than those sleeping over 7 hours. That effect is larger than any supplement on this page produces, and it’s free.
Does elderberry help prevent colds and flu?
The evidence is insufficient. The NIH’s National Center for Complementary and Integrative Health states there isn’t enough evidence to determine whether elderberry helps with colds or flu, and the available studies are small and use varying preparations. It’s unlikely to hurt you, but it shouldn’t replace a flu vaccine or anything else with better evidence.
Should I take vitamin D to avoid getting sick?
Only if you’re actually deficient. Supplementation reduces respiratory infection risk in people with low baseline levels and does little in people who are already replete. Get a serum 25-hydroxyvitamin D test rather than guessing, and don’t exceed the 4,000 IU per day upper intake level for adults without your doctor’s direction.
How do I tell the difference between a cold and the flu?
Colds come on gradually over one to three days, mostly above the neck, with little or no fever. Flu arrives abruptly, often within hours, with fever, body aches, headache and exhaustion. If it’s flu, call your doctor within 48 hours, because antiviral medications work best when started early. COVID overlaps with both and needs a test.
When should I call a doctor for a cold or flu?
Call for trouble breathing, chest pain, confusion, signs of dehydration, a fever that returns after improving, or symptoms lasting past about 10 days without improvement. Any fever in an infant under 3 months is an emergency. Call sooner if you’re pregnant, over 65, immunocompromised, or managing asthma, diabetes or heart disease.
About the author
Priya Shetty, MS, RD, is the Wellness Editor at The Culture Mom. She’s a registered dietitian with a master’s in nutritional sciences and nine years of clinical and community nutrition practice, and she reads the primary literature before she writes about it. She is not a physician and does not give medical advice. Read more of her work on the editors page.