Vitamin D supplementation to reduce COVID-19 morbidity in older adults

September's Paper of the Month is from the Journal of Nutritional Science and is entitled: ‘COVID-19: the older adult and the importance of vitamin D sufficiency’ by Paula M. O'Shea, Tomás P. Griffin, Michelle Brennan and Eamon C. Mulkerrin.

In December 2019, in Wuhan, China, the novel coronavirus “severe acute respiratory syndrome 2” (SARS-CoV-2) was discovered as the cause of a pneumonia-like illness (COVID-19) and is now a global pandemic. While older people do not appear to be at an increased risk of contracting COVID-19, they are more vulnerable to developing serious complications and have the highest death rate. Many older people have more than one disease occurring at the same time (e.g., cardiovascular disease, diabetes and frailty) that deplete their reserves and weaken their immune response. However, this does not fully explain the preponderance of particularly severe COVID-19 infections in older people. Through the process known as immunosenescence, the immune system, including its ability to recognise, activate the system, obliterate and remove a virus such as SARS-CoV-2, is impaired in an extremely unpredictable fashion with increasing age. Moreover, a chronic increase in systemic inflammation, known as “inflammaging”, thought to arise from an overactive but less effective immune alerting system is more prominent with increasing age. There is impressive evidence that “inflammaging” in association with sedentary lifestyle habits, obesity and nutritionally unbalanced diets, is a major driver of the release of too many signalling molecules (cytokine storm) which can result in the immune system attacking the body. Cytokine storm is associated with up to half of the fatalities in COVID-19 infections. Considerable experimental evidence demonstrates the immuno-modulatory properties of vitamin D, in particular, its role in regulating and suppressing the inflammatory cytokine response to viral respiratory infections linking the importance of vitamin D sufficiency as a potential protective factor in COVID-19. The main physiological causes of vitamin D insufficiency are lack of exposure to sunlight, the concentration of melanin in the skin and the capacity of human skin to synthesise vitamin D. Older adults are at increased risk of vitamin D deficiency as they produce 75% less cutaneous vitamin D than young adults, even with regular sun exposure. Other risk factors for vitamin D deficiency include reduced oral intake, nutritionally deficient diets, liver and kidney impairment, all of which occur more frequently in older people, with residents of care institutions at particular  risk. 

A recent study of over 11,000 individuals found that regular daily vitamin D supplementation of up to 2000 IU safely reduced the risk of respiratory infections. 

The protective effects of supplementation with vitamin D were stronger in those with the lowest baseline vitamin D levels. Given what has been described as a “pandemic of vitamin D deficiency”, especially in Europe and in the context of the SARS-CoV-2 contagion, we support the call for public health doctors and physicians, with support from Governments, to prioritise and strengthen recommendations on vitamin D intake and supplementation. Randomised controlled trials of vitamin D supplementation in patients admitted with COVID-19 to determine if such a strategy shortens duration of illness or improves response are warranted.