Can Vitamin D Positively Impact COVID-19 Risk and Severity Among Older Adults: A Review of the Evidence

Background: The coronavirus Covid-19 strain that emerged in December 2019, continues to produce a widespread and seemingly intractable negative impact on health and longevity in all parts of the world, especially, among older adults, and those with chronic health conditions. Aim: The first aim of this review article was to examine, summarize, synthesize, and report on the research base concerning the possible use of vitamin-D supplementation for reducing both Covid-19 risk and severity, especially among older adults at high risk for Covid-19 infections. A second was to provide directives for researchers or professionals who work or are likely to work in this realm in the future. Methods: All English language relevant publications detailing the possible efficacy of vitamin D as an intervention strategy for minimizing Covid-19 infection risk published in 2020 were systematically sought.


Introduction
The COVID-19 or pandemic remains an intractable problem despite months of study and investigation of the many possible causes, as well as strategies for amelioration or prevention. At the same time, adults with a variety of chronic health conditions may not be able to either access or receive optimal care due to many travel and other social restrictions. This narrative report focuses on vitamin D as a possible antidote to the widespread risk of severe illness on acquiring this virus, as well as for mediating its severity, and fostering a more rapid return to health. Since offset excess risk of Covid-19 and its consequences must be sought as argued by Simonson [1]. In this regard, mounting evidence points to a possible role for vitamin D in explaining infection risk, as well possible benefits of intervening in this regard to offset or minimize this risk.
Although research in this realm is clearly in its infancy, and based largely on observational studies, Covid-19 infection and death rates do appear to be notably higher in the elderly than any other sub group, and this may be mediated in part, by the presence of a prevailing vitamin D deficiency. Since many adults suffer from this particular deficiency, it can be argued that a proportion of Covid-19 cases may be preventable. Since vitamin D sources are several, potential efforts to attain adequate sunlight exposure, exposure to foods or beverages containing vitamin D, and/or supplementation of vitamin D in vulnerable adults may be more beneficial than not.
Indeed, if found to be influential in any way, intervention in this regard may provide one avenue that is reasonably practical for purposes of securing the wellbeing of the aging person, especially in the case of the chronically ill older adult that alone can heighten risk of infection due to its overall potentially debilitating effect on immune, musculoskeletal and cognitive health.
Others may be given medications that render them more prone to Covid-19, and less likely to be 'good' surgical candidates or ventilator candidates if they have severe disabling chronic health conditions, especially those who may also be vitamin D deficient.
This work is significant because the ability to minimize Covid-19 risk and severity is currently of the highest importance, especially among the elderly confined to their homes in isolation, as well as nursing homes, or to situations that limit sunlight and nutrient based vitamin D exposure. As discussed by Mok et al. [2], the Covid-19 pandemic proceeds unabated, despite considerable public health efforts to mitigate this spread. The development of a vaccine is still awaiting confirmation, and even then vaccinations may be only part of the solution. However, other compounds with antiviral properties may be helpful to consider not only in the interim, but in the future.

Aims
This narrative review aimed to specifically examine the value of vitamin D therapy for or minimizing the risk of acquiring Covid-19 infections in the older population, especially those with preexisting vitamin D deficits. Its second aim was to offer recommendations for future consideration by clinicians and researchers in the field based on these findings.

Materials and Methods
To obtain the data for this review, the electronic data sources PUBMED, Scopus, and Web of Science were searched. The time period searched ranged from January 1 2020-December 2, 2020 and the key words included Covid-19, vitamin D, coronavirus, older adults. All forms of study or analysis were deemed acceptable. However, because most empirical studies are in process, and unpublished, and no consistent intervention approach could be identified among these trials, a narrative summary of all available data including case studies, and uncontrolled observational studies was implemented.
Selected material had to focus on vitamin D related facts relevant to infection risk and recovery, as well as symptoms of infection in the older adult. Excluded were articles that did not focus specifically on this set of issues and non English based articles. Preprints were used to highlight the possible scope and updated findings concerning this present topic, rather than for prescribing clinical guidelines.

Results
Of the more than 60,000 publications on Covid-19, published as of December 2 2020, a total of 307 articles potentially relevant to the current topic were listed on PUBMED. Very few additional articles were found on the additional web sites. In terms of the topic of interest to this report, however, only 75 articles were deemed relevant as more publications than not did not meet criteria for this review, for example, they discussed vitamin D in children, or were letters to the editor. Even when the topic of the listed publication was relevant, it was clear that the prevailing reports were predominantly literature reviews, rather than actual studies. These were not uniform however, and tended to discuss studies with considerable variation in the samples studied, as well as This is important to note, given that according to Zemb