The average adult gets 2-4 respiratory infections per year, with the majority occurring between October and March.
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Coeheal Editorial Team
Coeheal Editorial Team
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Coeheal Editorial Team
Editorially reviewed for accuracy against cited sources. This is an editorial review, not a medical or clinical review. For personalised health advice, consult a qualified healthcare professional.
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Vitamin D deficiency: UVB radiation is insufficient for vitamin D synthesis above 35 degrees N latitude from approximately October to March. Vitamin D activates production of cathelicidin and defensins; deficiency is associated with 40-50% increased respiratory infection risk. A 2017 meta-analysis of 25 RCTs found vitamin D supplementation reduced acute respiratory infections by 12% overall and by 70% in severely deficient individuals. Circadian disruption: shorter days disrupt the circadian rhythm, which regulates natural killer cell activity, T-cell proliferation, and cytokine production. Indoor crowding increases viral transmission. Low humidity reduces mucociliary clearance efficiency.
Vitamin D3: target 40-60 ng/mL; most adults in northern latitudes need 2,000-4,000 IU/day through winter; take with vitamin K2 (MK-7, 100-200 mcg/day) and a fat-containing meal. Zinc: 15-25 mg/day of bisglycinate or picolinate; do not exceed 40 mg/day without supplementing copper. Vitamin C: 500-1,000 mg/day. Elderberry: 5-10 ml standardised syrup daily as preventive, or 300 mg extract daily. Omega-3 (EPA+DHA): 1-2 g/day. Probiotics: Lactobacillus rhamnosus GG or Bifidobacterium animalis BB-12; 10 billion CFU/day.
Key immune-supporting nutrients: Vitamin A - essential for mucosal immunity; found in liver, eggs, dairy, and orange/yellow vegetables. Vitamin C - found in bell peppers, kiwi, strawberries, broccoli. Zinc - found in oysters (richest source), red meat, pumpkin seeds, legumes. Selenium - 2 Brazil nuts per day provides the RDA. Iron - supplement only if deficient. Gut health: approximately 70% of the immune system is in the gut-associated lymphoid tissue (GALT). Prebiotic fibre (onions, garlic, leeks, asparagus, oats) feeds beneficial bacteria. Fermented foods (yogurt, kefir, sauerkraut, kimchi) provide both probiotics and immune-supporting compounds.
Sleep: a 2015 study found people sleeping less than 6 hours were 4.2 times more likely to develop a cold when exposed to rhinovirus than those sleeping 7+ hours. Aim for 7-9 hours; consistent sleep and wake times; cool bedroom (18-19 degrees C). Exercise: 150-300 minutes of moderate-intensity activity per week; regular exercisers have 40-50% fewer upper respiratory infections than sedentary individuals. Stress management: a 2012 meta-analysis found psychological stress was associated with a 2-fold increase in cold susceptibility. Nasal hygiene: saline nasal irrigation; a 2019 RCT found daily nasal irrigation reduced cold duration by 1.9 days.
Ashwagandha (KSM-66 or Sensoril): reduces cortisol by 15-30% in RCTs; 300-600 mg/day; particularly useful for high-stress individuals. Astragalus: enhances NK cell and T-cell activity; 500-1,000 mg/day standardised extract. Reishi mushroom: beta-glucans stimulate macrophage and NK cell activity; 1,000-2,000 mg/day. Andrographis: strong evidence for reducing cold duration and severity; a 2017 Cochrane review found it significantly reduced cold symptoms; 200-400 mg/day standardised extract; most effective started at first symptoms. Garlic: 2-4 raw cloves daily or aged garlic extract (Kyolic) 600-1,200 mg/day.
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