Lifestyle Guides


Boost Your Immunity Against COVID, Colds, and Flu

   AUTHORS: Miles Hassell, MD & Shelly Johnson, MSN, RNC-MNN, NPD-BC ©2023

   Lifestyle tools are updated as new evidence becomes available and our peer review process is complete.

   Literature review current through: 10/4/2023.  Topic last updated: 12/2/2023.

   This topic is sponsored by the founding board members. 

   Editorial policy


 Printable How-To Guide


These lifestyle tools target common seasonal respiratory tract infections caused by viral (and sometimes bacterial) infections.  Sometimes these will be labeled as the common cold, influenza, COVID-19, sinusitis, bronchitis and pneumonia.  All of these can have manifestations ranging from mild to life-threatening, and may have manifestations outside of the respiratory tract including fatigue, skin rashes, nerve and other organ injury.


The COVID-19 pandemic highlighted the prominence of lifestyle-modifiable health risks associated with severe respiratory illness.  One study looked at associations between underlying health conditions and COVID-19-associated hospitalization using a retrospective cohort study of electronic health record data for 7,452 adults over age 18 with a positive COVID-19 SARS-CoV-2 test.  For all age groups, hospitalization incidence was higher for those with underlying health conditions.[1]  57.4% of those hospitalized had high blood pressure, 49.7% were obese, 41.2% had chronic metabolic disease, and 32.9% had type 2 diabetes;[1] that adds up to an enormous number of potentially preventable hospitalizations.  The U.S. COVID-19-associated hospitalization surveillance network (COVID-NET) reported 92% of adults hospitalized with laboratory-confirmed COVID-19 had at least one underlying condition that was probably lifestyle related.[2]  Another analysis suggested that the majority of serious COVID-19 cases were associated with obesity or obesity-related disease.[3]  Out of 906,849 COVID-19 hospitalizations in adults in the U.S., 30% were attributable to obesity, 26% to hypertension, 21% to diabetes, and 12% to heart failure; together, these accounted for over 60% of hospitalizations.[3]  The mechanisms for poor outcomes and higher mortality for obese people with COVID-19 include higher inflammation levels, immune response, and T-cell activity.[4]  Patients with type 2 diabetes and metabolic syndrome may be up to ten times more likely to die when they become ill with COVID-19.[4]


A survey of 592,571 participants examined how often they ate 27 different food items, and found higher diet quality scores, especially of vegetables, fruits and legumes, was associated with lower risk of COVID-19.[5][11]  The NutriNet- Santé Cohort with 7,766 adults suggested that diets rich in fruits, vegetables, and food sources of fiber, vitamin C, and vitamin K were associated with a decreased probability of COVID-19 infection.[6]  Other studies also identified the Mediterranean diet with lower rates of inflammatory disease.[11]


Highly processed food intake is associated with a broad range of poor health outcomes, as well as increased COVID-19 infection and death.[7]  Dietary intakes from 41,012 UK Biobank participants found that people who ate the most highly processed food had more hypertension, diabetes, chronic kidney disease, lung disease, and increased odds of COVID-19 incidence.7  Potential mechanisms for a relationship between highly processed food and respiratory illness include pro-inflammatory effects, and suppression of normal immune response.[7]


  • Physical inactivity, obesity, and smoking appear to be independently associated with higher risk of community-acquired pneumonia and dying from pneumonia.[8] A UK Biobank analysis of 387,109 participants that examined lifestyle factors and COVID-19 cases that resulted in hospitalization suggested physical inactivity, obesity, and smoking were major predictors of severe COVID-19 infection.[8]
  • Physical exercise as well as improved diet and reduction in obesity improved immune surveillance and antiviral response in severe cases of COVID-19 and lowered rates of acute respiratory infection, pneumonia, and death from infectious respiratory illness. [9]


All great changes of constitution are more likely to be effected by alterations of diet and modes of life, than by medicine…and [diet] affords hope and consolation to the patient, in a disease where medicine is known to be unavailing, and surgery affords no more than a temporary relief.  -Hippocrates [10]


Regular exercise, an omnivorous whole food diet pattern, weight management and sleep are the foundations for dramatically reducing risk of serious influenza, COVID-19 and other respiratory illness.


Aim for physical activity sufficient to achieve increased breathing effort (shortness of breath) 1-3 times a day, even if it is very brief: anything is better than nothing.  Moderate exercise such as brisk walking, a total 30-60 minutes daily is a reasonable target.  It is likely that higher intensity exercise for short periods is adequate, too. Include both upper and lower body exercise, aiming to get short of breath and sweaty, depending on the individual capabilities/conditions.[8][9]


Focus on year-round lifestyle habits aimed at building an overall robust immune system and reduced preventable risk during times of increased infectious illnesses.

Omnivorous diets plentiful in whole foods like the Mediterranean pattern – These diets (featuring olive oil, fruits, vegetables, whole intact grains, legumes, nuts, seeds, fish, eggs, and dairy) not only demonstrate immunomodulatory effects and protect against chronic low-grade inflammation, but also protect against atherosclerosis, cardiovascular disease, cancer, and neurodegenerative diseases.[11]

Probiotic foods containing ‘good bugs’ -- Include frequent full-fat plain yogurt and kefir, personally sweetened with honey or fruit, and other probiotic foods (such as fresh sauerkraut/1 tablespoon of apple cider vinegar diluted in water to taste/kimchi) to support the immune system.[12]

Avoid highly processed foods, refined grains (foods made with any type of flour) and sugars.[5][7]  For practical purposes, consider processed foods to be any food prepared outside of the home.

REDUCE WAISTLINE IF APPROPRIATE -- Excessive abdominal fat mass remains one of the major factors for reduced immunity and chronic disease.[1][2][3]


Poor sleep and sleep disorders can predispose to suppressed immunity and increase risk factors of obesity, insulin resistance and type 2 diabetes.[13][14][15]  Poor sleep is recognized as a risk factor affecting airway immunity, increasing risk of severe respiratory infection that can progress to chronic airway disease.[16]  It also increases fatigue and reduces exercise tolerance and overall quality of life.[16]


  •  Vitamin C supplementation has failed to show significant benefit for reducing the risk of getting respiratory infections, but may shorten the duration of respiratory illness. 500-1,000 mg of vitamin C twice a day during illness is reasonable.[17] More importantly, including fresh fruits and vegetables daily has more robust data for improving disease resistance.
  • Vitamin D deficiency is thought to contribute to increased COVID-19 infection rates, and acute respiratory distress syndrome.[18][19]  Naturally occurring vitamin D, such as from sunlight exposure and frequent oily fish consumption, seems to have the greatest benefit.  So far, Vitamin D supplements have been disappointing for improving health outcomes: most studies show no benefit from supplementation, and where there is benefit using vitamin D for respiratory illness, the benefit is very modest.  A systematic review and meta-analysis of 46 randomized controlled trials showed a reduced risk of acute respiratory illness of 1.0% (61.3% of the vitamin D group vs. 62.3% of the placebo group) compared with placebo group.[20]
  • Zinc -- Reduced zinc levels impact antiviral immune response and zinc-rich foods (seafood, eggs, meat, seeds, nuts, whole grains and legumes) are thought to improve immune response.[21] While zinc supplements to prevent COVID-19 and other respiratory illness is unimpressive,[22] zinc lozenges (acetate or gluconate) during respiratory illness may reduce illness duration.[23]  The utility of zinc lozenges seems to be tied to the ability of a slowly dissolving oral application to release zinc ions around the oropharyngeal region, a common cold portal of entry.[23]


A systematic review and meta-analysis of 14 randomized controlled trials concluded honey as superior to the usual home care for cough frequency and severity.[24]  A partially double-blinded, randomized trial of 105 children ages 2-18 found honey to be most favorable for symptom relief (children had less cough frequency, less cough severity, less bothersome cough, better sleep, and even their parents had better sleep), over Dextromethorphan syrup and no treatment.


The role of community mask-wearing for respiratory viruses is, at best uncertain, which means a healthy immune system is even more important.[25]


A Cochrane review examined 19 trials comparing hand hygiene with controls (i.e. no intervention) in schools, childcare centers, and homes to find a 14% relative reduction in the number of people with respiratory illness in the hand hygiene group; they suggested a reduction from 380 respiratory events per 1,000 people to 327 per 1,000 people.  Pooled data suggested an 11% relative reduction in respiratory illness, suggesting a reduction from 200 events per 1,000 people to 178 per 1,000.  Hand hygiene seems to be a harmless, cost-effective,[26] common sense intervention affordable and accessible to most.


[1]McConnell, K., et al. Association Between any Underlying Health Condition and COVID-19-associated Hospitalization by Age Group, Washington State, 2020–2021: A Retrospective Cohort Study. BMC Infect Dis 2023; 193(23) 23.

[2]Kim, L., et al. Risk Factors for Intensive Care Unit Admission and In-hospital Mortality Among Hospitalized Adults Identified through the US Coronavirus Disease 2019 (COVID-19)-Associated Hospitalization Surveillance Network (COVID-NET). Clinical Infectious Diseases 2021; 9(72), 206-214.

[3]O’Hearn, M., et al. Coronavirus Disease 2019 Hospitalizations Attributable to Cardiometabolic Conditions in the United States: A Comparative Risk Assessment Analysis. JAHA 2021; 10:e019259

[4]Petrakis, D., et al. Obesity: A Risk Factor for Increased COVID 19 Prevalence, Severity and Lethality (Review). Molecular Medicine Reports 2022; 22, 9-19.

[5]Merino, J., et al. Diet Quality and Risk and Severity of COVID-19: A Prospective Cohort Study. Gut 2021;70: 2096-2104.

[6] Deschasaux-Tanguy, M., et al. Nutritional Risk Factors for SARS-CoV-2 Infection: A Prospective Study Within the NutriNet-Santé Cohort. BMC Med 2021; 290(19).

[7]Zhou, L., et al. Impact of Ultra-processed Food Intake on the Risk of COVID-19: A Prospective Cohort Study. Eur J Nutr 2023; 62, 275–287.

[8]Hamer, M., et al. Lifestyle Risk Factors, Inflammatory Mechanisms, and COVID-19 Hospitalization: A Community-based Cohort Study of 387,109 Adults in UK. Brain, behavior, and immunity 2020. 87, 184–187.

[9]Da Silveira, M., et al. Physical Exercise as a Tool to Help the Immune System Against COVID-19: An Integrative Review of the Current Literature. Clinical and Experimental Medicine 2021; 21, 15-28.

[10]Wadd, W. 1816. Cursory Remarks on Corpulence; or Obesity Considered as a Disease: with a Critical Examination of Ancient and Modern Opinions, Relative to its Causes and Cure, 3rd ed. London: J. Callow, Medical Bookseller.

[11]Casas, R., et al. The Immune Protective Effect of the Mediterranean Diet against Chronic Low-grade Inflammatory Diseases. Endocrine, Metabolic & Immune Disorders – Drug Targets 2014; 14, 245-524.

[12]Strauss, M., et al. Probiotics for the Prevention of Acute Respiratory-Tract Infections in Older People: Systematic Review. Healthcare 2021; 9: 690.

[13]Cappuccio F., et al. Meta-analysis of Short Sleep Duration and Obesity in Children and Adults. Sleep 2008; 31: 619-626. doi: 10.1093/sleep/31.5.619

[14]Anothaisintawee T., et al. Sleep Disturbances Compared to Traditional Risk Factors for Diabetes Development: Systematic Review and Meta-analysis. Sleep Med Rev 2015; 30: 11-24. doi: 10.1016/j.smrv.2015.10.002

[15]Richter, K., et al. Sleep Quality and COVID-19 Outcomes: The Evidence-based Lessons in the Framework of Predictive, Preventative and Personalized (3P) Medicine. EPMA Journal 2021; 12: 221-241.

[16]Locke B., et al. OSA and Chronic Respiratory Disease: Mechanisms and Epidemiology. Int J Environ Res Public Health 2022; 19(9): 5473.

[17]Keya, T., et al. Effect of Vitamin C Supplements on Respiratory Tract Infections: A Systematic Review and Meta-Analysis. Current reviews in clinical and experimental pharmacology 2022; 17(3): 205–215.

[18]Teshome, A., et al. The Impact of Vitamin D Level on COVID-19 Infection: Systematic Review and Meta-Analysis. Frontiers in Public Health 2021; 9.doi: 10.3389/fpubh.2021.6245599

[19]Grant, W., et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Death. Nutrients 2020; 12(4): 988. doi: 10.3390/nu12040988

[20]Jolliffe, D., et al. Vitamin D Supplementation to Prevent Acute Respiratory Infections: A Systematic Review and Meta-analysis of Aggregate Data from Randomised Controlled Trials. Lancet, Diabetes and Endocrinology 2021; 9(5): 276-292.

[21]Mossink J. Zinc as Nutritional Intervention and Prevention Measure for COVID–19 Disease. BMJ Nutrition, Prevention & Health 2020; 3: doi: 10.1136/bmjnph-2020-000095

[22]Balboni, E., et al, Zinc and Selenium Supplementation in COVID-19 Prevention and Treatment: A Systematic Review Of The Experimental Studies. Journal Of Trace Elements Med & Biol : Organ. Society for Minerals and Trace Elements (GMS) 2022; 71, 126956.

[23]Hemila, H. Zinc Lozenges and the Common Cold:  A Meta-analysis Comapring Zinc Acetate and Zinc Gluconate, and the Role of Zinc Dosage. JRSM Open 2017; 8(5): 2054270417694291.

[24]Abuelgasim H., et al. Effectiveness of Honey for Symptomatic Relief in Upper Respiratory Tract Infections: A Systematic Review and Meta-analysis. BMJ Evid Based Med 2021; 26(2): 57-64.

[25]Jefferson, T., et al. Physical Interventions to Interrupt or Reduce the Spread of Respiratory Viruses. Chochrane Database of Systematic Reviews 2023; 1(1): CD006207.

[26]Bagepally B., et al. Cost-Effectiveness of Surgical Mask, N-95 Respirator, Hand-Hygiene and Surgical Mask with Hand Hygiene in the Prevention of COVID-19: Cost Effectiveness Analysis From Indian Context. Clin Epidemiol Glob Health 2021; 10:100702. doi: 10.1016/j.cegh.2021.100702


Disclaimer: This generalized information is a limited summary of evidence-based lifestyle tools. It is not meant to be comprehensive and should be used as a tool to help providers and patients understand and/or assess potential lifestyle treatment options. It does not include all information about conditions, treatments, pharmaceuticals, side effects, or risks that may apply to a specific patient; nor is it intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient's specific and unique circumstances. Patients should speak with a health care provider for complete information about their conditions, medical questions, and treatment options, including any risks or benefits regarding use of lifestyle tools and how they may compliment their pharmaceutical regimen. This information does not endorse any treatments or pharmaceuticals as safe, effective, or approved for treating a specific patient. The Comprehensive Risk Reduction Foundation and its affiliates disclaim any warranty or liability relating to this information or the use thereof. All rights reserved.

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