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Guide · Gut and immunity · by Alexandra Lasconi

Immunity: what the studies show, ranked by the evidence

Short answer. The habits with the clearest human data are sleeping 7 hours or more, moving most days and keeping stress in check. Probiotics and honey have moderate evidence for specific outcomes. Vitamin D helps mainly if you are low, and zinc, garlic and spice remedies have small or uncertain effects. No single food makes the immune system stronger on its own.

Sleep comes firstUnder 6 hours a night: 4.2 times more likely to catch a cold after exposure.
Then movement and stressBoth linked to fewer and shorter colds in large studies.
Remedies come lastHoney eases a cough. Most spice remedies have not been tested on infections.

Evidence labels: Strong consistent controlled trials or an authorised EU claim · Moderate controlled trials or large studies, with limits · Early small, pilot, laboratory or single studies.

01

The ranking

Ten habits and remedies, by strength of evidence.

 02

Your week, in practice

A checklist you can follow.

 03

The WITH ME honey macerate

Recipe, what one serving contains, safety.

 04

Questions

Vitamin D, zinc, honey, children.

01 · The ranking

#Habit or remedyWhat studies foundEvidence
1Sleep, 7 hours or more164 healthy adults were given a cold virus. Those who had slept under 6 hours a night the week before were 4.2 times more likely to develop a cold than those sleeping over 7 hours (see referenced study [1]).Moderate
2Aerobic exercise most daysAmong 1,002 adults followed through autumn and winter, those exercising 5 or more days a week had 43% fewer days with cold symptoms than those exercising 1 day or less (see referenced study [2]).Moderate observational
3Lower stress394 people were given cold viruses. Rates of infection and of colds rose step by step with their measured psychological stress (see referenced study [3]).Moderate
4ProbioticsA Cochrane review of 24 trials found fewer people with three or more colds, episodes about 1.2 days shorter and fewer antibiotic prescriptions, with low to moderate certainty. Most trials used specific strains as supplements (see referenced study [4]).Moderate
5Honey, during a coldA meta-analysis of 14 studies found honey improved cough frequency and severity more than usual care. Most studies were in children (see referenced study [8]).Moderate for symptoms
6Vitamin DA 2021 meta-analysis found a small reduction in respiratory infections (see referenced study [5]). The 2025 update, with over 61,000 people, found no statistically significant protection (see referenced study [6]). Correcting a deficiency still matters for other reasons.Moderate small or no effect
7ZincA 2024 Cochrane review found the evidence insufficient for firm conclusions. Zinc may shorten a cold by about 2 days, with more taste changes and nausea (see referenced study [7]).Early
8GarlicA Cochrane review found one trial: 24 colds with a garlic supplement against 65 with placebo, in 146 people, and judged the evidence insufficient (see referenced study [9]). With aged garlic extract, the number of colds did not differ but people had fewer days feeling unwell (see referenced study [10]).Early
9Fermented foodsDaily fermented foods lowered inflammatory markers in healthy adults; infections were not measured (see referenced study [11]). See the fermented foods guide.Early for immunity
10Turmeric (curcumin)Curcumin supplements lowered C-reactive protein, an inflammation marker, in trials in people with inflammatory conditions (see referenced study [12]). Not tested on infections.Early for immunity

02 · Your week, in practice

Every day

  • 7–9 hours in bed, same times. See Sleeping Beauty.
  • Protein at every meal; your number comes from the macros calculator.
  • Vegetables, fruit and legumes for fibre, and 1–3 portions of fermented food.
  • 10 minutes that lower your stress: a walk, breathing, no screens.
  • Wash your hands when you get home.

Every week and season

  • Aerobic exercise on 5 days: a brisk 30-minute walk counts.
  • Avoid stacking very hard sessions with short sleep.
  • Autumn and winter: test vitamin D (25-OH vitamin D) and correct a shortfall with your doctor. The vitamin D calculator explains the numbers.
  • During a cold: rest, fluids, and honey for the cough if you are over 1 year old.

03 · The WITH ME honey macerate, maximum concentration

A very concentrated macerate in raw acacia honey, with no added water and no fermentation step. Below is the recipe exactly as we make it, then what one serving actually contains, then the safety notes. Please read all three.

Honey macerate, maximum concentration

Makes about 600–650 ml, concentrated on purpose · 5 minutes · 24–48 hours macerating

Base

  • Raw acacia honey: 300 ml (about 420 g)
  • 2 medium lemons, peeled, with their pulp: about 300 g, blended

Active ingredients, high amounts

  • Fresh ginger: 150 g
  • Fresh turmeric: 80 g, or turmeric powder: 40 g
  • Raw garlic: 50 g (about 8–9 large cloves)
  • Freshly ground black pepper: 8 g
  • Ground cloves: 6 g
  • Ground Ceylon cinnamon: 4 g

Method

  1. Put all the ingredients in a blender and blend for about 20 seconds, until completely smooth.
  2. Transfer to a sterilised glass jar and close it tightly.
  3. Leave at room temperature for 24–48 hours, opening the jar once a day for a few seconds.
  4. Then keep it in the fridge.

How to take it

  • 20–25 ml a day, after a meal, for 14–21 days.
  • Keeps 3–4 weeks in the fridge.
  • Not on an empty stomach. Avoid during severe, active gastritis. Not for children under 3.

What one serving actually contains

600–650 ml divided into 20–25 ml servings gives 24–32 servings. We used 28. The amounts are our arithmetic; the study doses are from the references.

IngredientPer serving (about)What studies usedReached at this dose?
Raw acacia honey15 g (about 12 g sugars)Honey during a cold, for cough symptoms [8]Similar to a spoonful used for cough. Studied during a cold, not taken daily to prevent one.
Fresh ginger5.4 g (roughly 1 g dried)Under 1.5 g dried ginger a day eased nausea in pregnancy trials [13]Yes, for nausea. Not studied for infections.
Turmeric2.9 g fresh (about 15–30 mg curcumin) or 1.4 g powder (about 40 mg)Several hundred to 2,000 mg curcumin a day, often in better-absorbed forms [12]No. Roughly 15 to 100 times lower. Food amounts cannot reach trial doses.
Black pepper0.3 g (about 15–25 mg piperine)20 mg piperine with 2 g curcumin raised curcumin absorption about 20-fold [14]Piperine yes; but the curcumin it acts on is small.
Raw garlic1.8 g (about half a clove)Allicin capsules in the one cold trial; 2.56 g a day aged garlic extract [9] [10]No. Allicin is also unstable, so less remains after days in the jar.
Lemon pulp11 g (about 6 mg vitamin C)—Flavour and acidity. Vitamin C is far below the 80 mg daily reference.
Cloves, Ceylon cinnamon0.2 g and 0.15 gMainly laboratory studiesFlavour amounts.
Go deeper: what a higher dose would and would not unlock

Ginger is the one active already in its studied range. Curcumin would need concentrated extracts, not more root: doubling the turmeric would still leave you far below trial doses and would make the mix much harder on the stomach. Garlic trials used standardised supplements, which a kitchen recipe cannot match. Honey's evidence is for soothing a cough during a cold, so the amount matters less than the timing.

Food safety: read before making it. Honey keeps on its own because it contains very little water. This recipe blends about 600 g of wet ingredients into 420 g of honey, so the mix is no longer dry enough to protect itself. At room temperature it can start to ferment: bubbles, a fizzy or alcoholic smell, a lid that lifts. Raw garlic in a low-oxygen mix is a known botulism risk when it is not acidic enough or not kept cold (see referenced source [15]). The lemon makes the mix acidic, but home batches are not pH-tested. So:
  • Use a sterilised jar and clean equipment.
  • Do not leave it out longer than 48 hours. For the lowest risk, put it in the fridge straight after blending.
  • Throw it away if the lid bulges, it smells rotten or yeasty, or you see mould.
  • Never give honey to babies under 12 months (see referenced source [16]).
Talk to your doctor first if you: take blood thinners or antiplatelet medicines (garlic, ginger and turmeric can add to their effect); have gallbladder disease or gallstones (see referenced source [17]); have diabetes (about 12 g sugars per serving); have reflux, gastritis or an ulcer; are pregnant or breastfeeding; or have surgery planned.

Myths and facts

MythFact
The more immune foods you eat, the stronger your immunity.The largest effects in studies come from sleep, movement and stress, not from any single food.
High-dose vitamin D prevents colds.The latest meta-analysis of over 61,000 people found no significant protection. Test, and correct a shortfall.
Garlic, ginger and turmeric are proven antivirals.Their antiviral effects come from laboratory studies. In people, the evidence on infections is limited or missing.
What the evidence does not show. No food or remedy here has been shown to prevent infections in a large, well-run trial. The honey macerate has not been studied as a recipe; the table shows what its ingredients bring at the amounts in one serving. If you have a fever over 3 days, trouble breathing, or keep getting ill, see your doctor.

Questions clients ask

Can any food make my immune system stronger?

No single food has been shown to. The clearest data are for sleep, regular exercise and stress, with probiotics and fermented foods behind them.

Should I take vitamin D in winter?

Test 25-OH vitamin D first and correct a shortfall with your doctor. The latest large meta-analysis found no significant protection against respiratory infections from supplements overall.

Does zinc help a cold?

A 2024 Cochrane review found the evidence insufficient. Zinc may shorten a cold by about 2 days, with more taste changes and nausea.

Is honey good for a cough?

A meta-analysis found honey improved cough frequency and severity more than usual care. Never give honey to babies under 12 months.

Can I take the honey macerate every day?

The recipe is designed for 20–25 ml a day for 14–21 days, after a meal. Check with your doctor first if you take blood thinners, have gallbladder disease or diabetes, or are pregnant.

Can children have the macerate?

Not under 3 years, and honey of any kind never under 12 months. For older children, ask your paediatrician; the raw garlic and spice are strong.

Sources

  1. Prather AA et al. Behaviorally assessed sleep and susceptibility to the common cold. Sleep (2015).
  2. Nieman DC et al. Upper respiratory tract infection is reduced in physically fit and active adults. Br J Sports Med (2011).
  3. Cohen S, Tyrrell DA, Smith AP. Psychological stress and susceptibility to the common cold. N Engl J Med (1991).
  4. Zhao Y, Dong BR, Hao Q. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev (2022).
  5. Jolliffe DA et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of aggregate data from randomised controlled trials. Lancet Diabetes Endocrinol (2021).
  6. Jolliffe DA et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol (2025).
  7. Nault D et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev (2024).
  8. Abuelgasim H, Albury C, Lee J. Effectiveness of honey for symptomatic relief in upper respiratory tract infections: a systematic review and meta-analysis. BMJ Evid Based Med (2021).
  9. Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database Syst Rev (2014).
  10. Nantz MP et al. Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms. Clin Nutr (2012).
  11. Wastyk HC et al. Gut-microbiota-targeted diets modulate human immune status. Cell (2021).
  12. Gorabi AM et al. Effect of curcumin on C-reactive protein as a biomarker of systemic inflammation: an updated meta-analysis of randomized controlled trials. Phytother Res (2022).
  13. Viljoen E et al. A systematic review and meta-analysis of the effect and safety of ginger in the treatment of pregnancy-associated nausea and vomiting. Nutr J (2014).
  14. Shoba G et al. Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers. Planta Med (1998).
  15. NC State Extension. Making garlic and herb infused oils at home (botulism risk of garlic in low-oxygen mixtures).
  16. NHS. Foods to avoid giving babies and young children.
  17. NIH National Center for Complementary and Integrative Health. Turmeric.

This page is nutrition coaching information, not medical advice. It does not recommend any product.

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