Vitamin D not only is well-known as a sunshine vitamin for bone health but also is essential for non-bone cells including immune cells, as shown in
Fig.1 (7,12) . Besides, Vitamin D can regulate anti-inflammatory responses by inhibiting pro-inflammatory cytokines. Cytokine storm is considered as a deadly disaster in response to SACR-CoV-2 infection and/or secondary infection because they can damage multiple organs and lead deaths (15). Vitamin D has also been well-reported as part of
the potential process of fighting many infections including
Tuberculosis, HIV, hepatitis C virus, bacterial vaginosis and colds and
flu. Vitamin D receptor on the plasma membrane of immune cells regulates
the signalling pathways of vitamin D in the immune response. There are
six identified major VDR gene polymorphisms including Cdx, A1012G,
FokI, BsmI, ApaI and TaqI (8). Some ongoing studies also
explored the susceptibility to coronavirus of an individual is possibly
depended by Vitamin D receptor genes relating to our immune responses
against the virus differ between individuals. For example, immune cells
called macrophages play an essential role in immune responses to viral
infections. In particular, activated macrophages may intracellularly
produce cathelicidin against viruses. Evidence shows Vitamin D is like
the key that fits in the lock as the VD receptor on the plasma membrane
of macrophages and turns it to open the door and activate these
macrophages (9). Once activated, they increase the production of
cathelicidin to fight the virus. A review article by William Grant and
colleagues supposed that vitamin D probably reduces the risk of infectious
diseases, including COVID-19, and minimize relevant deaths (10).
An optimal Vitamin D level for an individual in a reduction of the
infection remains unclear. The answer is probably determined by the VDR
gene polymorphism. This might reflect the individual difference in the
immune response as well as the effectiveness of vitamin D consumption.
In a recent article published by Hoang Anh Nguyen, VDR gene
polymorphisms particularly Fokl should be taken into consideration for
COVID-19 and vitamin D’s antimicrobial strategy (11). A study by
Marina Laplana and colleagues demonstrated that the Fokl is
significantly associated with the susceptibility to enveloped virus
infection (8). Notably, FokI is also related to obesity(7).
Despite the promising effects of vitamin D, few ongoing studies have
examined the preventative and therapeutic effect of vitamin D on
COVID-19. An ongoing trial by Cédric Annweiler and colleagues (2020) is
investigating the effect of high dosages of Vitamin D supplementation of
400,000 IU in a single oral dose on the elderly aged 70 and above in
France, compared with standard dosages of 50,000 IU (13). In
another trial by Manuel J Castillo and co-workers (2020), the COVID-19
patients with mild symptoms in Spain will receive a standard medical
treatment incorporating Vitamin D supplementation of 25,000 IU(14). To our knowledge, no studies explore the precise dosages
of vitamin D on COVID-19. Understanding genetic susceptibility to
SAR-CoV-2 is challenging, but it has the potential to fill the gap of
knowledge between the stratification of patients and personalised
treatment. Thus the governments, researchers and consumer genomics labs
across the globe should work on further vitamin D and COVID-19 study to
figure out a bigger picture on precision strategy. It is a possibility
that the VDR gene polymorphisms, probably FokI, may support a
personalised treatment for COVID-19. Ethical issues and confidential
relating to genetic data sharing should be carefully taken into account.