By Aliya Khan MD, FRCPC, FACP, FACE, Rowena Ridout MD FRCPC, Heather Frame MD FCFP, Claudia Gagnon MD, Lianne Tile MD MEd FRCPC, Wendy Ward M.Sc., Ph.D., David A. Hanley, MD, FRCPC, Sandra Kim MD, FRCPC

Previously we have described the role of vitamin D in optimizing bone health and treatment strategies for osteoporosis. In light of the current COVID-19 pandemic, the effects of vitamin D on modulating the immune system are being reviewed.

Two recent studies have suggested that low levels of vitamin D may be associated with an increased risk of severe COVID-19 infections.

Ilie and colleagues from the UK noted that countries with low levels of vitamin D had a higher number of COVID cases, as well as the highest mortality rates from COVID (1)). Similarly, Daneshkhah and colleagues from Northwestern University(2) also found that severe COVID-19 infections appeared to be more common in countries where vitamin D deficiency is more common. We recognize that the number of cases of COVID identified in each country will clearly be affected by the number of tests completed, as well as preventive measures taken by the various countries which were not accounted for in these studies. In addition, linking an observation of low vitamin D levels in a population with an illness needs to be interpreted with caution due to the limitation of confounding factors. At this time it is not known if low vitamin D levels are causally associated with a higher number and severity of COVID infections. Keeping that caution in mind, the possible link between vitamin D deficiency and an impaired immune response to COVID-19 infections may have some support from earlier studies of vitamin D effects on the immune system.

Vitamin D deficiency reduces the ability of white cells to mature and to produce antigens necessary to prevent infections (3) Vitamin D may prevent macrophages from releasing excessive inflammatory cytokines and chemokines (4)). Vitamin D may also enhance expression of ACE2 (Angiotensin converting enzyme 2), which has been associated with improved outcomes with COVID-19 infections (5, 6 )

These early observations may suggest that adequate vitamin D levels are of value in the immune response to infections such as from COVID-19. This would be of particular importance in patient populations vulnerable to low vitamin D levels. These include those who are obese, have malabsorption or short gut syndrome, long term anticonvulsant use as well as the elderly. However, further research is needed to determine if low vitamin D levels are causally associated with a higher number and severity of COVID-19 infections.

While the relationship between vitamin D and COVID-19 is unclear, we know that vitamin D is critical for bone health. Osteoporosis Canada recommends that individuals with osteoporosis or with risk factors for fractures receive adequate vitamin D, as recommended at 800-2000 IU per day. This would also be important for those at higher risk of developing vitamin D deficiency. High dose vitamin D supplementation should be avoided due to potential harms..

References

1. Ilie et al Aging Clinical and Experimental Research May 6, 2020
2. Daneshkhah et al Northwestern University May 2020
3. Abu-Amer et al 1993 Cell Immunol 151: 356-368
4. Helming et al Blood 106: 4351-4358
5. Kuka et al 2006 Curr Opin Pharmacol 6: 271-276
6. Cui et al 2019 Redox Biol 26: 101295