3 ms·

> There is a strong correlation between Vitamin D levels and COVID-19 outcome, They didn't adjust for confounders like BMI or poverty. https://www.nice.org.uk

by DanBC 6y ago

> There is a strong correlation between Vitamin D levels and COVID-19 outcome, They didn't adjust for confounders like BMI or poverty. https://www.nice.org.uk/advice/es28/chapter/Factors-for-decision-making https://www.nice.org.uk/advice/es28/chapter/Factors-for-deci... > Evidence was from 5 published studies in peer-reviewed journals. One observational cohort study (D'Avolio et al. 2020), 3 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. None of the studies were intervention trials of vitamin D supplementation for the prevention or treatment of COVID‑19. > Four of the studies found an association or correlation between a lower vitamin D status and subsequent development of COVID‑19. However, 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). 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 1 study. 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.

thu2111 6y ago
Is it valid to treat ethnicity as a confounder for vitamin D given that the belief is dark skin colour in northern climates results in lower vitamin D?
gridlockd 6y ago
"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." A couple of problems with interpreting that study: First, it only looks at infections, not course of infection. The million-dollar question is not whether Vitamin D prevents an infection altogether, but how high the risk for a severe course of COVID-19 is, given a Vitamin-D deficiency. Secondly, it adjusts for ethnicity and the "Townshend deprivation index" as a proxy for socio-demographics. You have to look at the huge impact of being classified as "black" (i.e. very dark skin color), and the large impact of being classified as "south asian" (likely moderately dark skin color). No other factor besides "poor health" even comes close. These people are largely Vitamin-D deficient, so by controlling for that factor, you are implicitly lowering the impact of Vitamin-D. It's like saying "Oh yeah your Vitamin-D levels are low but really the problem is that you're black". If you look at the controlled numbers, being insufficient in Vitamin-D becomes protective (OR ~= 0.9), which doesn't make any sense. "Townshend deprivation" measures household overcrowding and lack of access to a car, which are obviously factors that increase the risk of contracting any viral infection. Again, this shouldn't be controlled for in order to answer the question. Of course a single-variate analysis is not enough, because many diseases are causal for low Vitamin-D levels, but a multi-variate analysis with too many variables isn't meaningful.

by DanBC 6y ago

thu2111 6y ago

Is it valid to treat ethnicity as a confounder for vitamin D given that the belief is dark skin colour in northern climates results in lower vitamin D?

gridlockd 6y ago

"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." A couple of problems with interpreting that study: First, it only looks at infections, not course of infection. The million-dollar question is not whether Vitamin D prevents an infection altogether, but how high the risk for a severe course of COVID-19 is, given a Vitamin-D deficiency. Secondly, it adjusts for ethnicity and the "Townshend deprivation index" as a proxy for socio-demographics. You have to look at the huge impact of being classified as "black" (i.e. very dark skin color), and the large impact of being classified as "south asian" (likely moderately dark skin color). No other factor besides "poor health" even comes close. These people are largely Vitamin-D deficient, so by controlling for that factor, you are implicitly lowering the impact of Vitamin-D. It's like saying "Oh yeah your Vitamin-D levels are low but really the problem is that you're black". If you look at the controlled numbers, being insufficient in Vitamin-D becomes protective (OR ~= 0.9), which doesn't make any sense. "Townshend deprivation" measures household overcrowding and lack of access to a car, which are obviously factors that increase the risk of contracting any viral infection. Again, this shouldn't be controlled for in order to answer the question. Of course a single-variate analysis is not enough, because many diseases are causal for low Vitamin-D levels, but a multi-variate analysis with too many variables isn't meaningful.