Unexpected Approaches to Strengthen Your Immune System Ahead of Cold Season

Vitamin C, zinc, plenty of sleep – by now, most people know the standard advice for cold season. Less well known are three approaches that research has found to be surprisingly effective: a centuries-old water tradition, a look at gut flora, and targeted supplementation with bacterial cultures.

When does cold season actually begin?

When people hear "cold and flu season," they often think of the actual flu wave. According to the Swiss Federal Office of Public Health, this typically does not begin until between December and February, most often in January. The common cold, however, sets in considerably earlier. The main culprits are rhinoviruses, responsible for roughly 30 to 40 percent of all respiratory infections, which spread preferentially in autumn as soon as daycare centres and schools reopen and people spend more time indoors. At the same time, RSV season begins in October and continues into March.

In practice, this means the actual "cold season" already begins in September and October – weeks before public attention turns to flu vaccination. Anyone wanting to support their immune system therefore has a window of opportunity in late summer and early autumn that classic advice columns rarely address. This window is precisely the best starting point for all three approaches described below, since new habits can still be built up calmly before the actual wave of infections sets in.

Why the usual tips alone often fall short

Sufficient sleep, outdoor activity and a balanced diet remain the foundation of any immune preparation – that much has not changed. But these recommendations have been repeated so often that they barely register as concrete action points anymore. Things get more interesting with approaches that come up less often in everyday conversation, even though a solid body of evidence now exists for them. Three in particular are worth a closer look: an old water tradition, the composition of gut flora, and targeted supplementation.

First unexpected approach: what cold showers have to do with resilience

The idea of hardening the body with cold water runs deep in Swiss and wider German-speaking tradition. Sebastian Kneipp developed his water treatments in the 19th century, and water treading, cold pours and alternating showers have since been part of the standard repertoire at spa towns and Kneipp associations – including in Switzerland, where water-treading basins remain a fixture of many municipal parks today. For a long time, this practice was mainly passed down as experiential knowledge from generation to generation. That has changed: a Dutch randomised controlled trial with over 3,000 participants had one group take a 30, 60 or 90-second cold shower following their usual warm shower, over 30 days. The result: sickness-related work absences fell by 29 percent in the cold-shower groups compared with the control group.

The effect was particularly noticeable in perceived capacity to keep functioning despite mild symptoms – exactly how this mechanism works is a subject of ongoing research. Anyone wanting to try it is best off starting with just a few seconds at the end of a regular shower and gradually increasing the duration.

Second unexpected approach: how fermented foods influence the gut-immune axis

The close relationship between the gut and the immune system has long been known among specialists – yet in most people's everyday lives, this connection plays almost no role when preparing for the colder months. A controlled human study from Stanford University in 2021 measured this link directly: 36 healthy adults followed either a high-fibre or a fermentation-rich diet for ten weeks – yoghurt, kefir, sauerkraut, kimchi and similar traditional foods.

In the fermented-food group, gut bacterial diversity increased measurably, while the activation of several immune cell types and the concentration of nineteen inflammation-associated messenger proteins in the blood both decreased. The high-fibre comparison group did not show this effect to a comparable extent over this short study period – a result the researchers themselves described as surprising, since a high-fibre diet is generally considered especially beneficial. Larger follow-up studies are now set to show how these effects translate into actual cold frequency. In Switzerland, there is no need to reach for exotic products to try this: sauerkraut, and lacto-fermented carrots and beetroot have been part of farmhouse winter provisioning for generations and supply the same living cultures as kimchi or kombucha. Anyone wanting to try this in practice can introduce fermented foods gradually and in small, everyday-friendly portions – a spoonful of sauerkraut or a glass of kefir a day, for example.

Approach	What the research observes	Study type
Cold showers (Kneipp tradition)	29% fewer sickness-related absences, no change in sick days	RCT (human, n = 3,018)
Fermented foods	Greater gut bacterial diversity, fewer activated immune cells and inflammatory markers	RCT (human, n = 36)
Targeted probiotic supplementation	Lower risk of at least one acute respiratory infection during the observation period	Systematic review (Cochrane, 12 RCTs)

Third unexpected approach: what the research says about targeted probiotics

Beyond the dietary route, the question arises whether gut flora can also be influenced in a targeted way through supplementation. The current 2022 Cochrane review evaluated twelve randomised controlled trials with over 4,000 participants on this question. For the adult subgroup – around 2,032 people across four studies – probiotic supplementation was associated with roughly a 21 percent lower risk of at least one acute respiratory infection during the observation period, compared with placebo or no treatment.

Further research is set to show how this effect translates to individual strains and dosages. Anyone interested in targeted supplementation is best off choosing products with transparent information on strain count, dosage and testing procedures.

Safety and use: what to keep in mind

Cold showers are generally safe for most healthy adults, but should be discussed with a doctor beforehand in cases of untreated high blood pressure, cardiovascular disease or Raynaud's syndrome. During pregnancy, intense cold stimuli are best avoided; a gentle start with short, lukewarm-to-cool pours is the gentler option.

Fermented foods are well tolerated by most people, though they can initially cause bloating in sensitive digestive systems, in which case intake should be increased more slowly. Caution is advised for people with pronounced histamine intolerance, as many fermented products are high in histamine.

Probiotic supplements are generally considered well tolerated for healthy adults, children, and during pregnancy and breastfeeding. An exception applies to people with severely weakened immune systems, central venous catheters, or those in intensive care – complications have been reported in isolated cases in these situations, so medical advice before use is sensible. Interactions with medication are rare; when taking antibiotics at the same time, it is advisable to leave a gap of a few hours, as antibiotics can affect the bacterial cultures.

Conclusion: what's shown – and what remains open

What unites these three approaches is that they lie outside the usual vitamin-C-and-zinc advice while still resting on a comprehensible body of evidence: fewer sickness-related absences from cold showers, altered immune activity from fermented foods, and a lower risk of respiratory infections from targeted probiotic supplementation. Research in this field keeps evolving – and all three approaches can already be worked into daily life easily and in parallel, ideally in the weeks before cold season properly sets in. As a complement to, not a replacement for, sleep, exercise and a balanced diet, which they pair well with.

This article is for general information purposes only and does not replace medical advice. If you have existing health conditions, are pregnant or breastfeeding, or are taking medication, it is recommended that you consult a doctor or pharmacist before applying the measures described or taking dietary supplements. Dietary supplements are not a substitute for a balanced and varied diet or a healthy lifestyle.