Introduction

COVID-19 continues to pose a threat to lives and livelihoods

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The COVID-19 pandemic has had profound adverse impacts across the world. As of 7 February 2022, 387 million confirmed cases have been recorded worldwide along with 5.7 million deaths,¹ though other metrics suggests excess deaths since the pandemic’s onset number 24.3 million.² Some COVID-19 survivors are left with lasting health problems notably ‘long COVID’, which can have life-derailing symptoms such as breathing problems, deep fatigue, joint pain, brain fog and heart palpitations.³ The pandemic is also having devastating impacts on jobs, businesses and economies.⁴

The process of vaccinating the world’s population is well underway, with over 10.2 billion doses administered as of 7 February 2022 and vaccinations proceeding at an average rate of 28 million per day.⁵ While national vaccination campaigns are making headway, full roll-out will take time. Worryingly, this process remains starkly inequitable, as reflected in counts of ‘fully vaccinated’ persons in countries from different income categories. As of 7 February 2022, these counts were: high income (72%), upper-middle income (75%), lower-middle income (42%) and low income (6%).⁶

Figure 1 illustrates these trends and breaks them down by country. It shows that high income countries are consistently well vaccinated, while low income countries are consistently poorly vaccinated. The two intermediate categories are more mixed, but in both cases one large country (represented by a big dot) stands out as better vaccinated than others and raises the average for its category, namely China for upper-middle income countries (UMICs) and India for lower-middle income countries (LMICs).

Figure 1: Vaccine coverage of population in different country categories, as of 7 February 2022 Click here to view Figure

Sandset laments the ‘state of acceptance of such inequities by some news outlets.⁷ Meanwhile, a joint statement by leaders from the charitable sector has argued that “in our interdependent world no one is safe until everyone is safe”.⁸

Vaccination efforts also face major challenges. Some countries continue to experience supply constraints, while many children remain ineligible for vaccines.⁹ Vaccine scepticism by some communities complicates uptake, especially when rooted in negative past experiences with the medical system.¹⁰ The proliferation of mutant SARS-CoV-2 variants raises thorny questions, such as implications for the infection rate, severity of illness and continued efficacy of vaccines.^12,13 In the meantime, the unvaccinated face greater risks than ever,⁵ even as some experts suggest vaccine escape is ‘inevitable’.¹⁴

If vaccination will take time and could prove complicated, relying chiefly on vaccinations to control the pandemic is risky.¹⁵ In such a scenario, examining complementary pandemic response options seems prudent.

Dietary measures as possible pandemic response options

Dietary measures including use of nutritional supplements offer possible pandemic response options that could complement medical and public health measures like vaccination and social distancing.

The capacity of diet and nutrition to support immune-system function vis-à-vis viral diseases is well-established. A recent review of evidence from humans and animals concluded that dietary supplements can offer a safe, effective and low-cost means to build immune resistance to viral diseases, and recommended nutrition be incorporated into government strategies to limit the impact of viral infections including COVID-19.¹⁶ A review of clinical trials examined the scope for supplements such as vitamins, minerals, nutraceuticals and probiotics to enhance immunity to viral infections like COVID-19. It found various supplements helped prevent or manage such infections and suggested they may be useful against COVID-19.¹⁷ In vivo experiments with mice found that dietary supplements can help them cope with coronavirus and other viral infections, and identified several as especially promising, including elderberry, selenium and spirulina.¹⁸

Conversely, deficiencies in protein, carbohydrates or nutrients can impair immune system function, and are associated with higher rates of viral infection and increased risk of morbidity and mortality.¹⁷ COVID-19 risk factors like obesity and metabolic syndrome are also linked in part to diet.^19,20 Poor nutrition can moreover delay COVID-19 recovery and compound complications for survivors.²¹

One scenario in which using foods or their bioactive extracts to boost immune function could be key to reducing disease risk is where communities face malnutrition, since this condition can impair the immune system, suppressing immune functions that are fundamental to host protection. Animal and human studies have demonstrated that adding deficient nutrients back to the diet can restore immune function and resistance to infections^.22

An estimated 811 million people currently face hunger while 2 billion are malnourished.²³ Widespread micronutrient deficiencies notably in parts of the Global South contribute to problems like intellectual impairment and decreased capacity for work.²⁴ Deficiencies of key nutrients – e.g., calcium, dietary fibre, omega-3 fatty acids – are also common in the Global North, notably among vulnerable groups.²⁵

This set of factors has led to calls for more research on the linkages between diet and disease, as well as stronger national programmes on diet.²⁶ The World Health Organization (WHO) issued dietary guidelines for the COVID-19 pandemic that call for eating certain foods while limiting use of others to reduce infection risk.²⁷ Target foods include fresh fruits and vegetables, whole grains, beans, nuts, fish and unsaturated fats. Those to eat less of include processed foods, salt, sugar and saturated fats like those found in fatty meats or butter. 

This diet resembles the ‘healthy reference diet’ elaborated by the Lancet Commission,²⁸ an expert body that issued a landmark report in 2019. This report sought to provide an ”evidence-based starting point” for addressing current realities of poor nutrition and unsustainable agricultural production.²⁹ It suggested that changes to diet and food production could create ‘win-win’ outcomes for human and planetary health.³⁰

Microalgae as a possible target food                                                                                                                               

Algae is a term that covers a diverse group of aquatic organisms ranging from freshwater microalgae to large seaweeds. Like plants, algae typically generate energy from sunlight via photosynthesis, but they differ from plants in basic ways, such as growing in water and lacking rigid cell walls. Some algae are seen as harmful, such as those that cause ‘algal blooms’ which can kill aquatic organisms by depleting oxygen.³¹ Others can be used to meet key human needs like food, feed and energy supply.

This review paper focuses on microalgae from the genus Arthrospira, which are commonly known as spirulina. These freshwater algae grow in alkaline water and are used as a dietary supplement, among other applications. Spirulina has been a traditional food for centuries in places where it occurs naturally, such as for the Kanembu people of Chad, and it was a key food for the Aztec civilisation.³²

Two factors explain the paper’s focus on spirulina as a possible pandemic response option. First, a pre-pandemic body of evidence suggested spirulina has antiviral efficacy against several viral diseases, making its efficacy against SARS-CoV-2 an obvious question. Second, a significant body of research and experience with spirulina already exists, so any evidence on its relevance to COVID-19 could be set in context. 

Materials and Methods

The present analysis asked whether spirulina may have efficacy as a means of reducing COVID-19 risk, given pre-existing evidence of its antiviral effects vis-à-vis other diseases. It examined this question via a narrative review of the academic literature conducted using Web of Science, PubMed, Cochrane, Scopus and Google Scholar. Two sets of searches were conducted, namely “spirulina AND COVID” and “spirulina AND pandemic”. All 25 papers identified were included in the analysis, given the small size of the evidence base in light of the short time for such evidence to accrue. All were published in academic journals except for one pre-print.³³

Analysis of the 25 papers identified included grouping them into categories then summarising their headline findings vis-à-vis spirulina and COVID-19, followed by a discussion. Aspects of findings most relevant to debates on pandemic response efforts were emphasised. The general benefits and risks of spirulina consumption were also briefly described.

This review has several characteristics that distinguish it from the prior reviews it cites. While some prior reviews considered whether different algae species might offer options to help manage COVID-19, this review focuses on one widely available alga that has been extensively studied. It aims to glean headline findings from studies along with their practical implications rather than report detailed technical analysis. It shares findings in non-technical language to foster wider access beyond academics in relevant disciplines. It considers how this alga may be particularly useful to pandemic response efforts in countries with large at-risk populations. 

This review also builds on these earlier reviews. Notably, it distils provisional lessons to support COVID-19 response efforts by public health authorities and households looking to manage pandemic risk. It also flags the need for further research into these linkages in terms that could resonate with potential enablers such as government officials and funding agencies.

The approach followed aims to foster wider recognition of this body of work to maximise the likelihood of follow up actions. It fits with the growing calls for opening up disciplinary ‘silos’ and embracing more holistic framings of issues to help address key societal challenges. An example is the call from some thought leaders to adopt a One Health perspective to address interlinked health, agricultural and environmental problems.³⁴

Results

The technological characteristics of spirulina include its profile as a crop and a food, among others. This paper focuses on spirulina as a dietary supplement, since this is the aspect that emerged from the review process.

Before reporting the review findings, the wider literature on the benefits of consuming spirulina is briefly summarised. The possible risks of spirulina consumption are also highlighted in the following discussion.

Wider literature on spirulina consumption

A significant body of literature exists on the health benefits of consuming spirulina.

A recent review of laboratory studies, in silico analysis and human trials assessed the health benefits of spirulina and its food industry applications.³⁵ Spirulina was reported to be the best known and most widely cultivated microalga worldwide whose use as a food supplement has been extensively studied. Its nutritional profile includes high protein content and diverse bioactive compounds including essential amino acids, minerals, B vitamins, pigments, and lipids like gamma linolenic acid and polyunsaturated fatty acids. Spirulina also demonstrates anti-oxidation, anti-inflammation, and anti-tumour activity and can reduce risks from various diseases or conditions, such as type-2 diabetes, obesity or hypertension.

Other sources likewise suggest spirulina can mitigate disease risk. One review of in vivo and in vitro studies mapped its pharmacological profile and reported various benefits, including antiviral, antibacterial, anticancer, immune-stimulant, antioxidant and metalloprotective (i.e., prevention against heavy metal poisoning) effects.³⁶ Another literature review found spirulina showed strong biological activity against various conditions while also promoting growth of beneficial gut microflora.³⁷ A third review found spirulina use was linked to antioxidant, immunomodulatory and anti-inflammatory effects, and suggested it offers a promising therapy for various diseases and conditions.³⁸ A review of randomised controlled trials on the efficacy of spirulina for treating diseases suggested it may ameliorate symptoms and have anticancer, antiviral and antiallergic effects.³⁹ Finally, spirulina use was found to boost immune system function of senior citizens and to slow age-related system decline.⁴⁰

The wider literature encompasses diverse studies that found spirulina boosted resistance to specific diseases. Examples include exhibiting anticancer activity of clinical significance,⁴¹ inhibiting replication of HIV-1/AIDS⁴² and foot-and-mouth virus⁴³, helping patients cope with hepatitis C⁴⁴, and improving blood parameters of patients with chronic obstructive pulmonary disease.⁴⁵ Some studies examined spirulina’s effects on influenza, another respiratory disease caused by an encapsulated RNA virus. For instance, one study reported that feeding spirulina to influenza-infected mice improved their survival rates, and suggested it might offer safe and effective therapeutic agent to help manage influenza outbreaks and hence merits further clinical investigation.⁴⁶

Review findings on spirulina and COVID-19

The early evidence on spirulina and COVID-19 was examined to assess the viability of this microalgae as the basis of possible response options to the pandemic.

The paper belongs to the literature on food supplements or extracts providing protection against pathogens like bacteria or viruses. Modes of action vis-à-vis viruses include boosting immune system function and interfering with viral pathways.⁴⁷ Interference with pathways can occur at different stages of viral infection, such as entering the body, transport through the body, infecting target cells or reducing disease severity.⁴⁸ Studies showing algal compounds exerting antiviral effects at different stages of viral pathogenesis suggest algae offer a highly promising source of antiviral compounds.⁴⁹

Consuming spirulina seems to help combat COVID-19 in different ways. One is supporting general immune system function thanks to being a potent nutritional supplement. Another is protecting against the SARS-CoV-2 virus via distinct anti-viral pathways. This evidence on COVID-19 and spirulina comes from human trials as well as in vivo, in vitro and in silico studies.

The three key categories into which the 25 papers identified fall are (i) examining antiviral properties vis-à-vis COVID-19 of compounds derived from spirulina; (ii) examining biological mechanisms linking spirulina with resistance to COVID-19; and (iii) spirulina as a potential COVID-19 response option of particular relevance to at-risk populations.

One group of papers explored how spirulina and perhaps also other algae might help society cope with COVID-19 via the antiviral properties of compounds derived from these organisms. Some of these papers are reviews of laboratory studies and/or human trials (Table 1), while others are based on computer modelling (Table 2).

Table 1: Antiviral activity of spirulina’s constituent compounds vis-à-vis COVID-19 based on diverse studies

Table 2: Antiviral activity of spirulina’s constituent compounds vis-à-vis COVID-19 based on modelling

Another group of papers explored biological mechanisms via which spirulina might help people cope with COVID-19. Some of these papers simply discuss relevant mechanisms and how they might prove useful (Table 3). Other papers discuss these mechanisms but also suggest that consuming spirulina or algal extracts could help people manage COVID-19 risk pending the outcome of further research on these linkages (Table 4). Notably, some authors also suggest spirulina might help people cope with mutant variants.

Table 3: Evidence on biological mechanisms via which spirulina might help people cope with COVID-19

Table 4: Evidence on biological mechanisms that is coupled with recommendations on early use of spirulina

A third group of papers reported evidence of linkages between spirulina use and COVID-19 while specifying that this microalga could be particularly relevant to at-risk populations as a COVID-19 response option (Table 5). This includes populations where vaccination rates remain low and/or where many face food insecurity.

Table 5: Evidence on spirulina as a COVID-19 response option that emphasises its utility to at-risk populations.

Finally, one paper identified diverged from the others, as it found no linkages between spirulina and COVID-19.⁷¹ It screened 51 medicinal plants via in silico analysis for their potential as a basis of drug development for COVID-19, but spirulina was not among those identified as particularly promising.

Discussion

Spirulina and COVID-19 risk

Given complications with pandemic response efforts, risks from COVID-19 could persist over time, creating scope for measures like dietary change to play a valuable role in pandemic response efforts. The findings of this review suggest spirulina may offer a complementary COVID-19 response option.

The evidence summarised suggests two ways in which consuming spirulina or its extracts may help reduce peoples’ COVID-19 risk. One is that it could support general health and immune system function, given its rich nutritional profile. Another is that it may also inhibit SARS-CoV-2 via distinct antiviral mechanisms. Based on these early findings, it seems that incorporating spirulina into diet might offer scope to decrease the risk or severity of COVID-19 disease, and hence reduce associated morbidity and mortality. Further research is needed to verify the linkages identified and their apparent prophylactic and therapeutic effects, as called for by the authors cited. Some of these authors (e.g., Table 4) nonetheless also recommended consuming spirulina in the interim as a safe means to potentially reduce pandemic risk.

Spirulina might be particularly useful vis-à-vis COVID-19 for populations in the Global South, notably those in poorer countries or districts. In such areas many face delays to vaccination and/or have limited access to medical care. Some also struggle to access ample, nutritious food. These risks could heighten vulnerability to COVID-19, but consuming spirulina may offer scope to mitigate such risks.

Even if spirulina has potential, accessing it could be a challenge given the high cost of most commercially available spirulina powders and tablets. This mirrors a problem with the Lancet healthy reference diet, where an examination of data from 159 countries suggested this diet could be unaffordable to many of the world’s poor.⁷² One possible solution would be to foster local production of target foods to facilitate access. For spirulina, such efforts could build on the work of charitable projects like Antenna Foundation in Niger⁷³ or Nasio Trust in Kenya, which promote community-based production.⁷⁴

Given its apparent potential, using spirulina as a dietary supplement may offer scope for people to enhance their resilience vis-à-vis COVID-19. Resilient systems are defined as those able to withstand shocks without losing their functionality.⁷⁵ Resilience building measures can minimise damages from a shock, for instance to health or assets, but may also foster positive outcomes like enhanced functionality. Resilience is a timely concept in a world facing growing instability and shocks. Resilience building is also central to the United Nations Sustainable Development Goals as both a poverty reduction measure and facet of climate action.⁷⁶

Caveats to these findings and possible risks

While the evidence cited offers grounds for hope that spirulina could help combat COVID-19, two caveats regarding these findings should be noted.

One crucial caveat is that evidence on the health effects of consuming spirulina is limited and often based on laboratory studies. Critically, there is a dearth of evidence based on randomised controlled trials, which are critical to verifying the efficacy of health-related interventions. Spirulina should thus be viewed as a possible pandemic response option requiring further investigation rather than a proven one.

Another caveat is that while spirulina may offer scope to reduce COVID-19 risk, it mustn’t be seen as a substitute for proven preventative measures like getting vaccinated and social distancing. A related concern is that bold claims about ‘miracle foods’ being able to prevent COVID-19 have been circulating on social media despite a lack of solid evidence.⁷⁷ While regrettable, the fact that some people make irresponsible claims must not be allowed to derail sober consideration of promising options and their potential significance.

Spirulina is deemed safe for human consumption by regulators in leading countries,⁷⁸ which fits with its status as a traditional food in some cultures. Two potential risks should however be noted: Those with autoimmune disorders could have an adverse reaction to it,⁷⁹ while poor cultivation practices could contaminate spirulina with toxins like heavy metals ⁸⁰ or biological agents like microcystins.^{81, 82} Risks from heavy metals due to spirulina consumption appear low, however. Al-Dhabi⁸³ examined the heavy metal concentrations in 25 commercial spirulina products from different countries and found concentrations were significantly below allowable daily intake levels. Minimising contamination risk during production is nonetheless important. One factor that reduces risk of biological contamination is that spirulina grows in highly alkaline water,⁸⁴ which is not tolerated by most aquatic organisms ⁸⁵. One way to reduce biological risks is varying the temperature or salinity of the culture medium in ways spirulina can tolerate but other organisms may not.⁸⁶

Scope for action 

Although the available evidence on spirulina and COVID-19 remains thin and provisional, it nonetheless suggests several concrete actions as part of COVID-19 response efforts. Notably, governments could support further research on spirulina or launch healthy eating campaigns including it, while households and communities could consume – and perhaps also produce – spirulina as a potential means of lowering their pandemic risk. 

Despite its potential, use of spirulina as a dietary supplement remains low across the world. Its limited market penetration to date is reflected in a global market of just $102 million per annum in 2017,⁸⁷ which for comparison was dwarfed by the $2 billion garlic market.⁸⁸ Global farmed spirulina production was 69,600 tonnes live weight in 2018, though this is deemed an underestimate due to missing data from key producers like France, India, Israel, Italy, Japan, Malaysia and the USA.⁸⁹

Several research priorities follow from this analysis, notably (i) further research on the antiviral activity of spirulina vis-à-vis SARS-CoV-2, including randomised controlled trials; (ii) assessing the efficacy of spirulina vis-à-vis other emerging viral diseases; (iii) finding ways to ensure spirulina production meets safety standards, and (iv) better understanding spirulina’s low market penetration despite its technological promise.

Some authorities have warned pandemics could become increasingly common in future due to factors like deforestation, industrial farming and climate change that are destabilising natural systems and making it easier for diseases of animal origin to jump between species. International trade and travel may then facilitate their rapid spread. Such diseases disproportionately affect the poor and those in less-developed countries. The ‘One Health’ approach holds promise for minimising such dangers by emphasising the interlinkages between human, animal and environmental health and addressing these issues synergistically.^{90, 91} Further investigations into the scope for microalgae to help address COVID-19 and other novel diseases would fit with such efforts.

Conclusions

The COVID-19 pandemic creates threats on several levels, notably to lives and livelihoods. COVID-19 risks could persist over time, given the complexities surrounding vaccination and mutant variants, among other issues. National responses have tended to focus on measures like vaccination and social distancing, but dietary change offers possible complementary response options. Spirulina is an edible alga that merits greater attention as a potential means of lowering pandemic risk. One priority is further investigating its promise and limits as a dietary supplement, including its anti-viral effects vis-à-vis SARS-CoV-2 and other pathogens. Pending the outcome of such research, early use of spirulina may offer a way for people to boost their capacity to resist COVID-19. One demographic that might particularly benefit is populations facing elevated pandemic risk due to factors like low vaccination rates or food insecurity – realities common in parts of the Global South.

Acknowledgements 

We would like to acknowledge the authors whose work we reviewed for asking difficult but timely questions.

Conflict of interest

The authors declare no conflict of interest.

Funding sources

The authors received no financial support for the research, authorship and/or publication of this article.

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