An extensive amount of research has now been published on the relationship between vitamin D and immune health, from demonstrating the physiological roles of vitamin D within the immune cells, tissues, and organs, to the observed relationship between vitamin D levels and disease outcomes. It is factual knowledge that the body needs a supply of vitamin D in order to effectively fight off certain infections and diseases. A new meta-analysis shows that this seems to be especially true in the case of COVID-19.
A review by Petrelli et al. included 43 studies with data from a total of 612,601 COVID-19 patients that had been published from the beginning of the COVID-19 pandemic through January 31, 2021. All papers included data on vitamin D and COVID-19 disease risk, severity, and/or mortality. The primary outcome of the review was to see if there was a difference between COVID-19 infection risk among individuals with or without vitamin D deficiency (defined as vitamin D levels below 20 ng/ml or 50 nmol/L). Secondary outcomes of the review were severity and death due to COVID-19, as well as the therapeutic effect of vitamin D supplementation.
Risk of COVID-19 infection was 50% higher among those whose vitamin D levels were below 20 ng/ml (50 nmol/L) compared to those whose levels were at least 20 ng/ml (P=.02).
Risk of severe COVID-19, defined as the need for intensive care and/or mechanical ventilation, was 160% higher among those with vitamin D levels below 20 ng/ml (50 nmol/L) compared to those whose levels were 20 ng/ml or higher (P<.01).
Risk of death due to COVID-19 was 22% higher among those with vitamin D levels below 20 ng/ml (50 nmol/L) compared to those whose levels were 20 ng/ml or higher (P<.01).
Vitamin D supplementation of various doses reduced the risk of severe COVID-19 disease by 73% (P<.01) and death by 59% (P=.01).
The combined set of studies that evaluated COVID-19 severity and vitamin D levels can be seen on the forest plot below.
The purpose of a forest plot is to help you “see the forest among the trees.” They are used often in a meta-analysis, such as this paper, to summarize the results from individual studies. The idea is to compare two categories for one outcome, in this case, highest vs. lowest vitamin D levels for risk of severe COVID-19 disease. The vertical line, labeled as 1, indicates that the risk of severe COVID-19 is the same for both categories. A relative risk less than 1.0 indicates lower risk with higher vitamin D levels and a relative risk above 1.0 indicates higher risk with lower vitamin D levels. In this plot, almost all of the points are to the right, showing a higher risk of severe COVID-19 disease with lower vitamin D levels. Each point also has an associated bar with it – this represents the 95% confidence interval used in statistics. In reality it means the point could be anywhere along that line. Finally the big diamond at the bottom is the aggregate risk for all of the studies, and represents the 160% increased risk of severe COVID-19 disease among those with lower vitamin D levels demonstrated by this review.
Vitamin D plays essential anti-inflammatory and antiviral roles within the body, and a deficiency can lead to decreased immunity and a lacking immune response. This review solidifies the already demonstrated importance of maintaining healthy vitamin D levels, especially for immune response against COVID-19. The GrassrootsHealth panel of international vitamin D scientists recommends a vitamin D level between 40-60 ng/ml (100-150 nmol/L) – what is your vitamin D level?
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