Vitamin D deficiency tied to severe COVID-19

A systematic review and meta-analysis of >8,000 adult and elderly patients with COVID-19 showed a positive association between vitamin D deficiency (ie, 25(OH)D <50 nmol/L) and severe COVID-19.

“A high prevalence of vitamin D deficiency was observed among individuals with COVID-19, especially the elderly,” said the researchers.

Despite the lack of association between vitamin D deficiency and COVID-19 infection (odds ratio [OR], 1.21; p=0.003), individuals with severe COVID-19 were 65 percent more likely to be vitamin-D deficient compared with those who had mild cases (OR, 1.65; p=0.122). [Crit Rev Food Sci Nutr 2022;62:1308-1316]

Vitamin D insufficiency (ie, <75 nmol/L) was also tied to increased hospitalization (OR, 1.81; p=0.872) and mortality due to COVID-19 (OR, 1.82; p=0.045).

According to the researchers, this could be attributed to lower exposure to sunlight and lower 7-dehydrocholesterol values in the skin, which compromises cutaneous synthesis of 25(OH)D in the elderly. [Bone 2009;45:423-426] Furthermore, ageing is accompanied by a myriad of chronic comorbidities that may influence COVID-19 severity, which are often treated with drugs that can interfere with blood vitamin D levels [Cien Saude Cole 2015;20:2489-2498; Mil Med Res 2020;7:4; Nutrients 2020;12:988]

Taken together, the findings suggest that evaluating serum vitamin D levels may be warranted in clinical practice. Vitamin D supplementation may also be considered in COVID-19 patients with vitamin D deficiency and insufficiency, said the researchers. “However, there is no support for supplementation among groups with normal blood vitamin D values with the aim of prevention, prophylaxis, or reducing the severity of the disease.”

Overall, it remains imperative to maintain adequate nutrition for optimum health in the context of the pandemic. [Rev Endocr Metab Disord 2020;21:495-507; Eur J  Clin Nutr 2020;74:1117-1121] “Therefore, correcting nutritional deficiencies is important for improving individuals’ health, independent of the presence of comorbidities,” the researchers said.

Limitations of the meta-analysis that need to be taken into context are the absence of confounders such as age, sex, comorbidities, and vitamin D dosage. [Crit Rev Food Sci Nutr 2020;61:2262-2276; Rev Endocr Metab Disord 2020;21:67-76] The use of hospital-based samples and secondary patient records may have also introduced biases. “Such variables are determinants of COVID-19 severity. Thus, it is necessary to consider these aspects in future studies,” said the researchers.

Future studies may also consider looking into the climate factor, as countries closer to the equator apparently had lower COVID-19 mortality rates than regions further from the equator. [Am J Infect Control 2020;48:1042-1044; J Infect Public Health 2020;13:1373-1380] “This is probably because UV radiation from sunlight increases with proximity to the equator, which can contribute to the prevention of vitamin D deficiency in populations,” the researchers noted.