A recent review of research published in the journal Diseases has shown that anti-inflammatory diets can be useful in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or reducing the severity of coronavirus disease 2019 (COVID-19).
The COVID-19 pandemic has put a significant burden on many countries' socioeconomic and healthcare systems, with more than 248 million infections and over 5 million deaths recorded to date.
Although COVID-19 remains asymptomatic or mildly symptomatic in the majority of infected people, it may cause severe life-threatening consequences in susceptible people, including older adults, immunocompromised patients, and those with comorbidities.
The primary hallmark of severe COVID-19 is hyperinflammation characterized by excessive secretion of cytokines and chemokines. As evidenced in the literature, interferon-gamma, interleukin (IL)-1, -6, and -18, and tumor necrosis factor (TNF) are the major cytokines involved in COVID-19-related immunopathological conditions. Such hyperactivation of the immune system is collectively known as "cytokine storm," which subsequently leads to immune cell apoptosis, delayed viral clearance, alveolar barrier disruption, and pulmonary injury.
It is well-documented in the literature that a healthy diet is important for the proper functioning of the immune system. Conversely, people with poor nutritional status appear to have weakened immune systems, making them more susceptible to viral infections. Given the pathophysiology of COVID-19, anti-inflammatory diets are expected to reduce immunopathological burdens of the disease.
In the current review article, the scientists have discussed the impact of anti-inflammatory nutritional approaches in preventing as well as managing SARS-CoV-2 infection.
The scientists included all articles that studied the impact of dietary micro/macronutrients on COVID-19-related hyperinflammation. They specifically selected clinical trials, randomized controlled trials, meta-analyses, and review articles published between January 2020 and June 2021.
After excluding non-human studies, preprint articles, and non-English articles, they finally selected and discussed 17 studies in the current review.
The studies selected in the review reported that COVID-19 patients with nutrient deficiency take longer to recover. In addition, the majority of hospitalized patients appeared to have at least one nutrient deficiency. As nutritional interventions for COVID-19 management, the studies primarily focused on some critical anti-inflammatory dietary components, including vitamins C and D, zinc, and omega-3 fatty acids, as well as the Mediterranean diet.
The Mediterranean diet, comprised of vegetables and fruits, legumes, fish, and olive oil, is known to have potent anti-inflammatory, immunomodulatory, antioxidant, and anti-thrombotic properties. It is well-documented that the Mediterranean diet is highly effective in managing cardiovascular, pulmonary, and metabolic diseases.
Regarding COVID-19 management, studies have shown that the diet effectively reduces the length of hospital stay and mortality rate in COVID-19 patients aged above 65 years. Moreover, the diet has been known to reduce the risk of SARS-CoV-2 infection as well as the short-term and long-term complications associated with COVID-19.
The Antiviral, anti-inflammatory, and immunity-boosting properties of vitamin D are well-documented in the literature. In addition, vitamin D reduces the production of proinflammatory mediators by minimizing the production of T-helper 1.
In severely ill COVID-19 patients, vitamin D supplementation has been shown to reduce the duration of intensive care unit (ICU) stay. Moreover, studies have shown that COVID-19 patients with vitamin D deficiency tend to have higher mortality rates and that vitamin D supplementation can reduce long-term immunological outcomes of COVID-19, such as prolonged elevation of IL-6 and interferon-gamma levels.
Although further research is needed to conclude any therapeutic benefit of vitamin D against COVID-19, most studies indicate that the extent of therapeutic benefits depends on the patient's prior vitamin D status. Thus, adequate vitamin D intake is generally recommended to prevent deficiency. The recommended dietary allowance of vitamin D is 600–800 IU/day.
The antioxidant property of vitamin C is well-documented. It acts as a cofactor in many biosynthetic pathways and facilitates antibody production. Moreover, dietary intake of 1 gm of vitamin C per day is known to reduce the production of proinflammatory cytokines (IL-6, TNF, and C-reactive protein) and increase the production of anti-inflammatory cytokines (IL-10).
In COVID-19 patients, intravenous infusion of high-dose vitamin C has been shown to reduce the duration of ICU stay and mortality rate. It also reduces the progression of COVID-19 symptoms. A phase 2 interventional study is currently going on to study the impact of vitamin C supplementation in COVID-19 patients.
The recommended daily allowance of vitamin C for adults is 90 mg/day. Although short-term use of vitamin C is safe, prolonged intake of high-dose vitamin C could induce adverse health conditions, such as oxalate kidney stone formation.
Omega-3 polyunsaturated fatty acids
Omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) exhibit the ability to inhibit proinflammatory cytokine production and produce less inflammatory pro-resolving lipid mediators, including prostaglandins, thromboxanes, protectins, and resolvins.
In SARS-CoV-2 infection, omega-3 fatty acids might play a beneficial role by regulating the lipid raft fluidity and subsequently disrupting the formation of spike – angiotensin-converting enzyme 2 (ACE2) complex. Currently, a clinical trial is underway to study the impact of EPA intake on SARS-CoV-2-infected patients.
Zinc is a crucial mineral required for immune cells and the proper functioning of T-helper and cytotoxic T cells. In COVID-19 patients, zinc supplementation has been shown to exhibit a potential anti-inflammatory response. Moreover, the mineral has been shown to reduce symptom intensity in SARS-CoV-2-infected patients.
The authors conclude, "no single diet or food item has been proven to prevent COVID-19 infections. Regardless, supplements have received a great deal of interest from both the public and the scientific community as an effective and low-cost method for controlling or mitigating COVID-19 infections. However, despite evidence that some supplements can affect outcomes in other respiratory tract infections, such as reduced inflammation marker levels, shortened ICU stay lengths, and incidence of infections, it is still unknown whether dietary supplements or nutraceuticals can therapeutically alter patient outcomes against COVID-19. Furthermore, there is little research linking them with the prevention of COVID-19. With the aid of larger-scale COVID-19 clinical trials and investigations, the therapeutic or preventative functions of a nutrient approach will likely be clarified. Until then, the public should focus on immunization through vaccination and prioritize appropriate nutritional status, and encouraging an active lifestyle."