During the COVID-19 pandemic, sales of nutritional supplements that are known to have an important role in immune function such as vitamins C, D and the mineral, zinc, increased substantially. Nevertheless, no trials of these supplements have been undertaken in patients with COVID-19 and therefore the true benefit is unknown.
Although vitamin C and D and zinc appear to enhance immunity, the lack of evidence of value in COVID-19 represents a major stumbling block to recommending that patients use these supplements to either prevent or reduce the severity of infection with COVID-19. Nevertheless, researchers from Kings’ College, London, wondered if they could get some insight of the potential value of these supplements from data collected as part of the COVID Symptom study app. The study has been running since late March 2020 and allows users to self-report a vast amount of data including demographics, core risk factors, COVID-19 symptoms and test results via a smartphone app. In fact, data collected from the app has already led to the acceptance of anosmia and skin rashes as important symptoms of COVID-19 infection. Using a yes/no question, the app enquires as to whether an individual uses any nutritional supplements on a regular basis, defined as more than three times a week. The app has a list of various supplements including probiotics, garlic, omega-3 fish oils, multivitamins as well as vitamins C, D separately and the mineral, zinc. For the present analysis, the team included a subset of participants who reported being tested for COVID-19 using either the PCR test or via serology and who reported that they used nutritional supplements. The primary outcome was the report of a positive test for COVID-19.
A total of 175,652 individuals self-reported using supplements regularly since the beginning of the pandemic. Analysis of their data showed a significant 13% reduced risk of testing positive for COVID-19 and regular use of multivitamins (odds ratio, OR = 0.87), supplementing with vitamin D (OR = 0.91), probiotics (OR = 0.86) and omega fish oils (OR = 0.88). In contrast, there was no statistically significant association for either zinc, vitamin C or garlic. Interestingly, these protective effects were only significant for females and this was seen across all age groups and body mass indices. No protective effect was seen for males although among men aged > 60 years, there was a positive association between use of zinc and vitamin C and testing positive for COVID-19.
While the associations were not huge, the researchers called for trials to test the protective effects of these nutrients before making any specific supplement recommendations
Louca P et al. Dietary supplements during the COVID-19 pandemic: insights from 1.4M users of the COVID Symptom Study app – a longitudinal app-based community survey. MedRxiv preprint doi: https://doi.org/10.1101/2020.11.27.20239087