Changes in 25-hydroxyvitamin D levels post-vitamin D supplementation in people of Black and Asian ethnicities and its implications during COVID-19 pandemic: A systematic review

Background: People of Black and Asian ethnicities have a higher infection rate and mortality as a result of COVID-19. It has also been reported that vitamin D deficiency may play a role in this, possibly because of the multi-gene regulatory function of the vitamin D receptor. As a result, increased dietary intake and/or supplementation to attain adequate 25-hydroxyvitamin D (25(OH)D) levels could benefit people in these ethnicities. The present study aimed to review the literature examining the changes in 25(OH)D in different types of vitamin D supplementation from randomised controlled trials in this population. 

Methods: This systematic review was conducted using the PRISMA guidelines. Electronic databases were systematically searched using keywords related to vitamin D supplementation in Black and Asian ethnicities. 

Results: Eight studies were included in the review. All the included studies found that supplementation of vitamin D (D₂ and D₃), regardless of dosage, increased 25(OH)D levels compared to a placebo. All trials in which participants were vitamin D deficient at baseline showed increased 25(OH)D levels to a level considered adequate. Two studies that used food fortification yielded smaller 25(OH)D increases compared to similar studies that used oral supplementation (10.2 vs. 25.5 nmol L⁻¹, respectively). Furthermore, vitamin D₂ supplementation yielded significantly lower 25(OH)D increases than vitamin D₃ supplementation. 

Conclusions: Oral vitamin D supplementation may be more efficacious in increasing 25(OH)D levels than food fortification of Black and Asian ethnicities, with vitamin D₃ supplementation possibly being more efficacious than vitamin D₂. It is recommended that people with darker skin supplement their diet with vitamin D₃ through oral tablet modes where possible, with recent literature suggesting a daily intake of 7000–10,000 IU to be potentially protective from unfavourable COVID-19 outcomes. As a result of the paucity of studies, these findings should be treated as exploratory.