Public Health England's 'COVID-19 rapid evidence summary: vitamin D for COVID-19', published yesterday (June 29th), comes after a flurry of studies linking vitamin D deficiency to more severe COVID-19 symptoms and mortality.
The government initiated the creation of this rapid report to set out the best available evidence on vitamin D for preventing or treating COVID‑19, or for the susceptibility to COVID‑19 based on vitamin D status.
It looks at five published studies in peer-reviewed journals. One observational cohort study (D'Avolio et al. 2020), three observational prognostic studies involving published data sets using correlation or regression (Hastie et al. 2020, Ilie et al. 2020 and Laird et al. 2020) and 1 case-control survey (Fasano et al. 2020) looked retrospectively at the association between vitamin D status and development of COVID‑19.
The report states that while four of these studies found an association or correlation between a lower vitamin D status and subsequent development of COVID‑19, confounders such as body mass index (BMI) or underlying health conditions, which may have independent correlations with vitamin D status or COVID‑19, were not adjusted for (D'Avolio et al. 2020, Fasano et al. 2020, Ilie et al. 2020 and Laird et al. 2020).
It adds that all five studies were assessed as being at high risk of bias, and therefore of very low quality of evidence and that none of the studies were intervention studies of vitamin D supplementation so no data on appropriate doses or adverse events was given.
"Vitamin D status was based on serum 25‑hydroxyvitamin D (25(OH)D) levels in 3 studies and the proportion of participants taking a vitamin D supplement in one study," the report states. "The largest UK study (Hastie et al. 2020) found an association between vitamin D status and COVID‑19 only in a univariable analysis (with this single potential causative factor).
"Importantly, no causal relationship between vitamin D status and COVID‑19 was found after adjustment for confounders such as comorbidity, socio-demographics, ethnicity, BMI and other baseline factors."
"Apart from Hastie et al. 2020, none of the studies adjusted for confounding factors, such as BMI, higher socioeconomic deprivation and poorer self-reported health, which may have independent correlations with vitamin D status or COVID‑19. Three studies (Hastie et al. 2020, Ilie et al. 2020 and Laird et al. 2020) used historic data up to 20 years old on serum 25(OH)D levels for their included populations.
"The use or reporting of COVID‑19 case and mortality data is also limited in all 3 studies, with differences in national and international reporting and screening meaning some countries data may not include milder or asymptomatic cases. All 3 of these studies had poorly reported methods for model selection, model fit and checking (either correlation or regression). Two studies (D'Avolio et al. 2020 and Fasano et al. 2020) are limited by the representativeness of their samples and issues with diagnostic criteria for either COVID‑19 or its sequelae."
To protect bone and muscle health, the UK Government advises that everyone needs vitamin D equivalent to an average daily intake of 10 micrograms (400 international units). They advise that all people should consider taking a daily supplement containing 10 micrograms vitamin D during autumn and winter months.
They also advise that people whose skin has little to no exposure to sunlight and ethnic minority groups with dark skin, from African, Afro-Caribbean and South Asian backgrounds, should consider taking a vitamin D supplement all year round. This advice would also apply to people whose skin has little to no exposure to sunlight because they are indoors shielding or self-isolating.
The report adds that a person's individual risk of vitamin D deficiency may have changed during the COVID-19 pandemic if they are spending more time indoors.
Therefore, UK Government advice during the COVID-19 pandemic is that everyone should consider taking 10 micrograms of vitamin D a day because they might not be getting enough from sunlight if they're indoors most of the day.
They advise that 10 micrograms of vitamin D a day will be enough and people should not take more than 100 micrograms a day because it could be harmful. If people take higher therapeutic doses of vitamin D, monitoring is recommended.
See the government's full evidence review for more information.