The COVID-19 outbreak, first reported on January 13, 2020, in Wuhan, China has become a serious global public health problem. The disease was caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has infected over 650 million people worldwide as of January 1, 2023 [1]. As for Taiwan, the Central Epidemic Command Center (CECC) reported the first case of COVID-19 on January 21st, 2020, followed by the first death associated with COVID-19 on February 15th, 2020. The first COVID-19 community transmission occurred in May 2021, and CECC raised a nationwide epidemic warning to Level 3 on May 19th, 2021. On April 28th, 2022, daily number of confirmed domestic COVID-19 cases exceeded 10,000 for the first time. Figure 1 illustrates the weekly new cases and deaths from January 21st, 2020 to December 25th, 2022.
![figure 1](https://i0.wp.com/media.springernature.com/lw685/springer-static/image/art%3A10.1186%2Fs12889-023-17607-2/MediaObjects/12889_2023_17607_Fig1_HTML.png?resize=685%2C352&ssl=1)
Weekly new cases and deaths in Taiwan between 2020 and 2022
COVID-19 affects the immune system by producing a systemic inflammatory response [2]. Common initial signs and symptoms include cough, fever, headache, fatigue, body aches, and diarrhea [3]. Some individuals with COVID-19 become severely ill, usually starting about 1 week after symptom onset; severe COVID-19 often involves progressive respiratory failure and may result in life-threatening pneumonia, multiorgan failure, and eventually death [2, 3]. Although COVID-19 is known to affect people across all lifespans, it has been shown that the most serious consequences occur in individuals with older age, individuals with chronic diseases, and those with impaired immune systems [4, 5].
Currently, there is a lack of data to support recommendations for or against the use of any vitamin, mineral, herb, fatty acid, or other dietary supplements to prevent or treat COVID-19. However, nutritional influence on the immune system has been well documented in the literature [6]. In general, where practicable, an efficient way to reduce the risk of viral infections is to regulate the actions of the inflammation mediators through adaptable risk factors such as diet and exercise [7]. As widely demonstrated in the literature, the intake of different nutritional supplements such as essential fatty acids, linoleic acids, essential amino acids, and vitamins and minerals can improve the immune response, especially where immunity can also be conditioned by nutrition deficiencies as in the presence of viral infections [8].
Nevertheless, dietary supplement sales have dramatically risen during the COVID-19 pandemic despite depressed economic conditions [9, 10]. Many people hoped that these products might provide some protection against SARS-CoV-2 infection and, for those who develop COVID-19, help reduce symptoms and disease severity [11, 12]. There are many vitamins and minerals necessary for the normal functioning of the immune system [13]. Commonly, the use of immune-modulating dietary supplements including vitamin B, vitamin D, ascorbic acid (Vitamin C), zinc, omega-3 fatty acids, and probiotics [14] has shown to have a positive effect on strengthening immunity [13, 15]. Additionally, the use of nutritional supplement is also influenced by season. For instance, the use of vitamin C and D nutritional supplements often increases during cold and flu seasons (typically known as autumn and winter seasons) [16, 17].
Vitamin B complex does not only build and maintain a healthy immune system but also potentially prevent or reduce COVID-19 symptoms [18, 19]. A study conducted on 9,189 adults aged between 20 to 69 years indicated higher intake of vitamin B5 could reduce the odds of COVID-19 by 47%, and a moderate intake of vitamin B12 had a protective effect on COVID-19 [19]. Vitamin C is well known for its antiviral properties, such as increasing interferon-alpha production, modulating cytokines, reducing inflammation, and restoring mitochondrial function [20]. Several studies have also shown that vitamin C reduces the risk associated with upper respiratory tract infections [20,21,22]. Vitamin D is known for its anti-inflammatory and antioxidant properties [23]. Vitamin D is also involved in the modulation of the immune response in infectious and autoimmune diseases [24]. A number of studies suggested that vitamin D inhibits the overexpression of inflammatory cytokines [25]. Probiotics modulate innate and adaptive immune responses, facilitating the immune system’s development and maturation. Therefore, the use of probiotics with anti-inflammatory effects could maintain the equilibrium of intestinal microecology and prevent secondary infection in COVID-19 [26].
Since nutritional supplements use appears to be increased in response to COVID-19 pandemic severity worldwide, the association between number of newly confirmed cases and deaths and nutritional supplement search interest becomes an interesting topic for further investigation. Previous studies had indicated both an increasing number of COVID-19 confirmed cases and deaths and the presence of COVID-19 outbreak led to an increased online search of immune-boosting related dietary supplements. Globally, the public believes the use of nutrients and herbs can improve self immunity to fight against COVID-19 infection, as well as improving overall health and wellbeing [12, 27]. Our World in Data Coronavirus Pandemic (COVID-19 dataset) provides a public aggregated global dataset on COVID-19 newly confirmed cases and deaths. It is widely used by journalists, policymakers, researchers and the public [28]. This dataset on the conronavirus pandemic is updated daily, publicly accessible, and allows users to select a specific country and tracks the newly confirmed cases and deaths. Both global and local (Taiwan) data on daily newly confirmed cases and deaths can be collected from Our World in Data dataset.
Google Trends is a search trend feature that shows how frequently a given search term is entered into Google’s search engine relative to the site’s total search volume over a given period of time. The benefits of Google Trends include showing information trends, networking on the Internet, and changes that can have a negative or positive effect on public health. Nowadays, Google Trends has been used in many studies to analyze the public’s search behavior [29]. Analyses of searches related to COVID-19 and nutritional supplements can reveal which nutrients are of the greatest interest and how that interest changes over time. Up to date, only a few studies have looked at Google queries about dietary supplements [27, 30]. In this study, we aim to compare the public interest in nutritional supplements pre- COVID-19 pandemic and during the COVID-19 pandemic (pre-COVID-19 pandemic: 2019; during the COVID-19 pandemic: 2020 to 2022) in Taiwan and worldwide.
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