Table 1 Summary of dietary recommendations of selected studies for strengthening the immune system against COVID-19Â
Author/Year | Study design | Nutrients or Foods or Lifestyle with immune-supporting roles | Recommendations | Score |
Adams KK., et al./ 2020 | Commentary | Vitamins C, D. zinc, silver, elderberry | Physicians and patients should not rely on dietary supplements to prevent or treat COVID-19 | Â |
Ali N./2020 | Narrative Review | Vitamin D | Vitamin D supplementation has been reported to protect against respiratory tract infections | 9 |
BourBour F., et al./2020 | Systematic Review | Protein, Omega-3 fatty acids, Vitamins A, D, E, B1, B6, B12, C iron, zinc, selenium | Following a balanced diet may play a vital role in prevention of COVID-19 Supplementation according to the RDA is recommended for most of healthy people who do not have sufficient intake of nutrients | Moderate |
Bousquet J., et al./ 2020 | Narrative Review | Cabbage, fermented milk products, Resveratrol | These foods may reduce angiotensin-converting enzyme activity or are anti-oxidants | 9 |
Briguglio M., et al./ 2020 | Opinion | Protein, vitamins A, D, E, B, Iron and micronutrients | Mal-nutritional status is associated with immune dysfunction and Malnourished individuals may be more susceptible to SARS-CoV-2 infection | Â |
Butler MJ., et al./ 2020 | Narrative Review | Healthy diet including foods high in fiber, whole grains, unsaturated fats and antioxidants Unhealthy diet including foods high in saturated fats, refined carbohydrates and sugar | Individuals recommended for healthy diet to boost immune function and refrain from unhealthy foods | 8 |
Calder PC., et al./ 2020 | Narrative Review | Vitamins A, B6, B12, C, D, E, folate Trace elements, including zinc, iron, selenium, magnesium, and copper Omega-3 fatty acids (EPA + DHA) | Suboptimal status of these nutrients negatively affects immune function and can decrease resistance to infections Supplementation with micronutrients and omega-3 fatty acids based on RDA, is a safe, effective, and low-cost way to support optimal immune function | 9 |
Author/Year | Study design | Nutrients or Foods or Lifestyle with immune-supporting roles | Findings | Score |
Carter SJ., et al./ 2020 | Perspective | Vitamin D Physical activity Obesity | Obesity may increase the risk of symptom complications following a positive COVID-19 diagnosis Calcitriol make protective effects from lipopolysaccharide- induced lung injury by modulating the expression of angiotensin-converting enzymes I and II Physical activity may effectively improve vitamin D status. Supplementation with vitamin D (D2 or D3) has been shown to protect from acute respiratory infections, among individuals exhibiting vitamin D deficiency | Â |
Cena H., et al./ 2020 | Mini Review | Healthy diet, Mediterranean diet | Healthy diet prevents undesired hyper-inflammation and might be useful for patients with mild signs of infection Mediterranean diet which is rich in polyphenols has immune-protective and anti-inflammatory properties | 8 |
Chakhtoura M., et al./ 2020 | Commentary | Vitamin D | Vitamin D metabolites reduce the expression of cytokines due to the viral infection. Modulation of macrophage chemotactic protein1, interleukin 8, type 1 interferon, TNF-α and reducing oxygen reactive species |  |
Ciavarella C., et al./ 2020 | Narrative Review | Sea food and fish oil, pomegranate, herbs and spices (curcuma, thyme, oregano, hot pepper, rosemary, sage, lemongrass) | These nutritional PPAR- γ agonists make an inhibitory effect on pro-inflammatory cytokines | 12 |
D’Avolio A., et al./ 2020 | Retrospective study- Brief report | Vitamin D status | The 25(OH)D level is significantly lower in SARS-CoV-2 PCR-positive patients than in PCR-negative patients |  |
Fan Y., et al./ 2020 | Narrative Review | Liquorice, garlic, ginger, turmeric, pomegranate, black pepper | Functional food plants with immunomodulatory and antiviral properties | 12 |
Gombart AF., et al./ 2020 | Narrative Review | Vitamins A, D, C, E, B6, and B12 Folate, zinc, iron, copper, selenium | Supplementation of these micronutrients may modulate immune function and reduce the risk of infection Vitamins C and D and zinc are nutrients with the strongest evidence for immune supporting | 10 |
Grant WB., et al./ 2020 | Narrative Review | Vitamin D | Vitamin D supplementation is required for many individuals to reach 25(OH)D concentrations above 30Â ng/mL, especially in winter | 12 |
Author/Year | Study design | Nutrients or Foods or Lifestyle with immune-supporting roles | Findings | Score |
Handu D., et al./ 2020 | Narrative Review | Nutrient-dense eating pattern and energy needs | Dieticians should advise consuming a nutrient-dense eating pattern to meet protein and energy needs, with oral supplementation when necessary, to prevent and treat malnutrition in adults with comorbidities and not infected with COVID-19 | 10 |
Iddir M., et al./ 2020 | Narrative Review | Protein, and micronutrients including vitamins A, D, C, E, Bs, zinc, selenium and iron omega-3 versus lower saturated, trans fat, and omega-6 fatty acids, low refined sugars, high fiber content such as whole grains, phytochemicals | Strengthening the immune system during the COVID-19 crisis can be obtained through healthy diet | 10 |
Jayawardena R., et al./ 2020 | Systematic Review | Vitamins A, D, E, C Trace elements, Zinc, Selenium, Copper, Magnesium, Nutraceuticals and probiotics supplements | Treating malnutrition and weight reduction in obese healthy subjects. Nutrition principles based on adequate nutrients could be useful in possible prevention of COVID-19.Selective micronutrient supplementations may be beneficial especially for vulnerable populations | Moderate |
Kara M., et al./ 2020 | Narrative Review | Vitamin D | Call attention for the possible association between severe vitamin D deficiency and mortality pertaining to COVID-19 | 10 |
Kieliszek M., et al./ 2020 | Narrative Review | Selenium | Selenite inhibits the entrance of viruses into the healthy cells and abolish their infectivity | 9 |
Mailhot G., et al./ 2020 | Narrative Review | Vitamin D | Vitamin D supplementation decreases the rates of viral respiratory tract infections | Â |
Mehta S./ 2020 | Rapid Report | Healthy diet | Adequate calorie intake and an optimal diet including variety of fresh fruit and vegetables, unsaturated fats, complex carbohydrate and sufficient protein and vitamin intakes | Â |
Messina G., et al./ 2020 | Narrative Review | Omega-3 fatty acids (flaxseed oil), Vitamin C (Oranges, lemons, mangoes) Polyphenols (epigallo-catechin 3 gallate in green tea), flavonoids (Red wine, oranges, red fruits and vegetables) | Modification of the dietary regimen to improve the levels of adiponectin could be very useful to prevent the infection | 10 |
Razzaque, M S., et al./ 2020 | Commentary | Zinc | Adequate zinc intake is important to protect from microorganisms, including viral infections | Â |
Roy A., et al./ 2020 | Narrative Review | Zinc, Curcumin | The cytokine suppression by curcumin can be related to clinical improvement in conditions associated with cytokine storm in viral infections | 9 |
Ribeiro, Kdds., et al./ 2020 | Commentary | Healthy diet, vitamins A, D, and E, minerals zinc and selenium, fiber, and essential fatty acids | Adequate dietary intake may be necessary to protect against inflammation of SARS-Cov-2 infection; Some nutrients including vitamins A, D, and E, minerals zinc and selenium, fiber, and essential fatty acids, have been reported to promote the immune system | Â |
Zabetakis I., et al./ 2020 | Narrative Review | Mediterranean diet, unhealthy diet Fruit and vegetables, fiber, Fish and fish oils, vitamins C, D, E, Zinc, copper | Following healthy diet which provides adequate nutrients will support immune function People who are deficient in some micronutrients may warrant supplementation or modify their dietary patterns | 10 |