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Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results

Our take —

In this study of 489 individuals who tested for SARS-CoV-2 and had vitamin D levels measured in the last year, it was found that vitamin D deficiency was associated with a positive COVID-19 diagnosis. While this study improves upon prior studies in its inclusion of only recent vitamin D readings, it is unclear for whom these results would be most relevant. There may be people missing from the sample and/or variables missing from the analysis which may bias the results – for example if those with Vitamin D deficiencies are more likely to have other underlying co-morbidities and this is not taken into account, the relationship between Vitamin D and COVID-19 risk may appear stronger or weaker than the actual risk.  While the authors suggest that these findings support a role of Vitamin D deficiency in COVID-19 risk, further research is needed examine this question in a less selected group of people.

Study design

Retrospective Cohort

Study population and setting

This was a retrospective cohort study using electronic health record data on those tested for SARS-CoV-2 between March 3 and April 10, 2020 within a Chicago health system to examine whether Vitamin D status before SARS-CoV-2 testing was associated with a COVID-19 diagnosis. A positive SARS-CoV-2 test was defined as any positive PCR test result; testing was only completed among those with symptoms admitted to the hospital or exposed health care workers experiencing symptoms of COVID-19. Vitamin D deficiency was defined as <20 ng/mL for 25-hydroxycholecalciferol or <18 pg/mL for 1,25-dihydroxycholecalciferol. Recent serum vitamin D levels and subsequent Vitamin D treatment regimens resulted in the following classifications: 1) likely deficient (last level deficient and treatment not increased), 2) likely sufficient (last level not deficient and treatment not decreased), and 3) uncertain deficiency (either last level deficient and treatment increased or last level not deficient and treatment decreased). Multivariable regression was used to assess the association between Vitamin D deficiency and COVID-19 diagnosis, adjusting for other demographic and clinical factors.

Summary of Main Findings

Among the 4313 individuals who had SARS-CoV-2 tests, 489 (11.2%) had a Vitamin D level measured in the year before testing and had complete data. Of those tested and included in this sample, 15% (71/489) tested positive for SARS-CoV-2. Overall, 124 patients (25%) were categorized as being likely Vitamin D deficient, 287 (59%) as being likely sufficient, and 78 (16%) as having uncertain status. In multivariable analyses, likely deficient vitamin D status compared with likely sufficient vitamin D status was associated with greater risk of COVID-19 diagnosis (relative risk, 1.77; 95%CI, 1.12-2.81; P = .02). Comparing those on treatment with likely vitamin D deficiency with those with sufficient vitamin D levels showed no difference in testing positive for SARS-CoV-2.

Study Strengths

The use of electronic health records, including demographic, laboratory, comorbidity, and medication history in the last year, allowed for the creation of a cohort and facilitated the examination of a novel question.

Limitations

In order to be included in this analysis, patients had to be symptomatic and admitted to the hospital (or symptomatic and have a known exposure for health care workers), have a vitamin D measure within the last year, and have complete data. It is unclear who these results and the implications of these results would be applied to given that this is a very selected group of people. For example, Vitamin D testing is usually recommended to those with osteoporosis or serious diseases of the digestive system, including inflammatory bowel disease, celiac disease, kidney disease, and others. Additionally, the authors did not provide rationale for their use of race in the model.

Value added

This study is among the first to examine the association between vitamin D deficiency and risk of COVID-19 diagnosis. The use of more recent vitamin D level measurements taken before SARS-CoV-2 testing and diagnosis is an improvement over other studies that used much older Vitamin D levels that may not have reflected a patient’s vitamin D status at the time of SARS-CoV-2 testing.

This review was posted on: 2 November 2020