Vitamin D plays a significant role in building and maintaining healthy bones. In light of the current COVID-19 pandemic, the effects of vitamin D on 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.

One study 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. Another study found that severe COVID-19 infections appeared to be more common in countries where vitamin D deficiency is more common. Many different factors may contribute to the number of COVID-19 cases identified in a particular country. These may include the number of tests performed to identify COVID cases, and public health measures taken to prevent the spread of disease, which were not accounted for in these studies.  The severity of disease can also be affected by many different factors, including age, underlying health conditions, and accessibility to health care. Hence, we need to be cautious in linking low vitamin D levels to COVID cases or severity, when other important factors have not been taken into account. At this time it is not known if low vitamin D levels are the cause of the 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 in earlier studies of vitamin D effects on the immune system. These early studies 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. This includes those who are obese, have a malabsorption syndrome or who have been treated with long-term anticonvulsant therapy as well as the elderly. However, further research is needed to determine if low vitamin D levels are a cause of 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. Taking more than 2000 IU per day should only be done after consultation with your healthcare provider.