COVID-19 in age-related neurodegenerative diseases: is there a role for vitamin D3 as a possible therapeutic strategy?

The coronavirus disease (COVID-19), identified in Wuhan, China, on December 2019, was declared a pandemic by the World Health Organization, on March, 2020. Since then, efforts have been gathered to describe its clinical course and to determine preventive measures and treatment strategies. Adults older than 65 years of age are more susceptible to serious clinical symptoms and present higher mortality rates. Angiotensin-converting enzyme 2 (ACE2) is a major receptor for some coronavirus infection, including SARS-COV-2, but is also a crucial determinant in anti-inflammation processes during the renin-angiotensin system (RAS) functioning - converting angiotensin II to angiotensin 1-7. The decline in ACE2 expression that occurs with aging has been associated to the higher morbidity and mortality rates in older adults. These observations highlight the importance of investigating the association between COVID-19 and age-related neurodegenerative disorders, i.e., Parkinson's and Alzheimer's diseases. A possible option to reduce the risk of COVID-19 is vitamin D supplementation, due to its anti-inflammatory and immune-system-modulating effects. It has also been suggested that vitamin D supplementation plays a role in slowing progression of Parkinson and Alzheimer. The present study is a literature review of articles published on the theme COVID-19, Parkinson and Alzheimer's diseases, and the role played by vitamin D. PUBMED, MEDLINE, and EMBASE databases were consulted. Results confirm neurodegenerative and neuroinflammatory effects of COVID-19, aggravated in Parkinson's and Alzheimer's patients, and the important role of vitamin D as a possible therapeutic strategy. Nevertheless, randomized controlled trials and large population studies are still warranted.