Does green tea help against infections?
For influenza there is reasonable evidence that green tea catechins are helpful; for most other infections the data are still at the laboratory or animal stage, so use it as a complement to standard prevention, not a replacement for it.
For influenza, green tea has the strongest supporting evidence. A meta-analysis of five randomised trials (884 participants) and three cohort studies (2,223 participants) shows that catechins from green tea reduce the likelihood of influenza by roughly one third when taken orally, and by nearly half in the cohort studies. Gargling or swallowing gave comparable results. The researchers themselves emphasise that large-scale long-term studies with fixed dosages are still lacking.
Against other viruses, the evidence is largely confined to laboratory results. The main active component, EGCG, inhibits a broad range of viruses in cell-culture research, including influenza virus, hepatitis B and C, herpes and HIV. Those laboratory concentrations are theoretically achievable in the body, but there is no clinical evidence that a daily cup of tea delivers the same concentrations. Against COVID-19, everything so far is theory and computer modelling, not human trials.
For bacterial infections the picture is more mixed. In the laboratory, EGCG also inhibits bacteria, including the hospital bacterium MRSA. The concentrations required for this are ten to a hundred times higher than those needed to inhibit viruses, and whether such amounts can be reached by drinking tea is not established. One small, non-blinded clinical study (64 patients) found that a tea-based ointment cured a skin infection in 81% of patients, comparable to standard antibiotics. That is interesting but too limited to draw firm conclusions.
For the common cold there are indications from observational research, but clinical evidence is lacking. Drinking green tea in normal quantities is safe. As a preventive measure alongside existing advice (such as annual influenza vaccination) it is certainly not an unreasonable choice, but it is not a substitute for conventional treatment when an infection occurs.
Evidence for influenza prevention comes from a meta-analysis (PMID 34209247). Antiviral laboratory data come from reviews (PMID 23072320, 34209485) and cell-culture studies (PMID 11684313, 32868200). Antibacterial laboratory evidence from a review (PMID 23072320). Impetigo clinical study: PMID 11138536. Common cold: review (PMID 30037024). COVID-19: reviews (PMID 34209485, 38291871).
Does sauna bathing help against infections?
There are preliminary indications that regular sauna bathing may have a beneficial effect on your immune system, but the evidence is too thin for firm conclusions. If you have joint complaints or an unusual skin condition, discuss it with your doctor before making it a regular habit.
Can too little sleep make you more susceptible to infections?
Too little sleep demonstrably makes your immune system more vulnerable, including to infections and vaccinations. Make sure you get sufficient sleep, even though the exact numbers and thresholds are not yet precisely known.
Does turmeric help against inflammation?
Curcumin has a biologically plausible anti-inflammatory effect and shows reductions in inflammatory markers across multiple studies, but the results are not consistent enough for a firm recommendation. If you want to try it, choose a formulation with piperine or a liposomal variant for better absorption, and discuss it with your doctor if you are taking any medications.
Is zinc beneficial for my immune system?
Zinc is beneficial for your immune system if you have a deficiency or belong to a risk group such as older adults or severely malnourished individuals; for the common cold, a dose of up to 30 mg per day may shorten symptoms, but high doses without an indication are more likely to be harmful than helpful.
Does regular exercise help against that creeping chronic inflammation?
Regular, moderate exercise demonstrably lowers inflammatory markers such as CRP and IL-6; training too intensely can reverse that effect, so moderate exercise three to five times per week is the best-supported choice.
Can you strengthen your immune system by eating more fibre?
Eating more fibre has a clear biological mechanism, but in healthy people it does not automatically lead to a measurably stronger immune system. Fermented foods appear to work more reliably for your gut microbiome; probiotic supplements are even risky when used alongside immunotherapy.