More COVID hospitalizations in people with higher BMI - adults and now children (perhaps due to lower vitamin D)
Overweight Children Faced Higher COVID-19 Risk Despite Vaccination, Singapore Study Finds - July 2026
Singapore: 255,477 children between September 2021 and August 2023. https://doi.org/10.1016/j.jvacx.2026.100878
"Compared with children of acceptable weight, those classified as overweight had 26% higher adjusted odds of infection during the Delta wave...and 20% higher during the Omicron period"
Asked Claude AI about COVID vaccination and BMI
This study found that vaccinated children with higher BMI were more likely got get COVID than normal BMI chldren. Has this higher BMI, higher COVID infection also be found in adults. I suspect lower vitamin D ==> more likely to get COVID infection
I'll look at the study you linked and then check whether the BMI–COVID association holds in adults, plus the vitamin D angle you're suspecting.I got the summary of the Singapore study from the meta description. Let me search for the adult BMI–COVID data and the vitamin D connection.Now let me check the vitamin D connection you're suspecting — specifically whether low vitamin D is linked to COVID infection risk, and whether vitamin D status might mediate the BMI relationship.I have solid data on all three questions now. Let me pull this together — you know this literature well given your work, so I'll be direct about what the evidence shows and where it's softer.
The Singapore study
The study you linked was a nationwide cohort of 255,477 children aged 5–11 in Singapore between September 2021 and August 2023, and found that children classified as overweight by BMI had a higher risk of COVID-19 infection during both the Delta and Omicron waves, even after Pfizer mRNA vaccination. Notably, vaccination substantially reduced hospitalization risk across all BMI groups, but overweight children remained more likely to become infected than acceptable-weight children.
Does the BMI–COVID link hold in adults? Yes — strongly
This is one of the most consistently replicated findings of the pandemic. A few anchors:
The evidence base is large and directionally consistent. A literature search on BMI and COVID returns over 500 papers, with a consistent finding of higher BMI associated with worse COVID-19 outcomes, and several hundred studies provide evidence that BMI is a strong linear risk factor for severe outcomes — roughly 5–10% higher hospitalization risk per additional kg/m². Importantly for your causal suspicion, genetic (Mendelian randomization) data concur, with hazard ratios rising ~14% per kg/m² higher BMI, which supports a likely causal rather than merely correlational relationship.
One nuance worth flagging: most adult studies measure severity/hospitalization/mortality, not infection acquisition. On severity the UK community study of 334,329 adults showed an upward linear trend in COVID hospitalization with rising BMI — odds ratios of 1.39 (overweight), 1.70 (obese stage I), and 3.38 (obese stage II) versus normal weight. The Singapore children's study is somewhat distinctive in isolating infection risk specifically. But the PREDIMED-Plus adult cohort did assess incidence, confirming that older age and obesity are cross-sectionally associated with increased COVID-19 risk (not just severity).
So: the higher-BMI → more-COVID pattern is well established in adults, most robustly for severe disease, and with supporting (if thinner) evidence for infection acquisition itself.
Your vitamin D hypothesis
Your instinct is well-supported by the observational literature, and there's a specific reason it ties the two threads together.
On infection risk directly, the largest meta-analysis found that in studies adjusted for confounders there was a higher risk of SARS-CoV-2 infection in the vitamin D deficiency group (OR 1.77; 95% CI 1.24–2.53), and a similar result in unadjusted studies (OR 1.75; 95% CI 1.44–2.13). An Israeli population-based study similarly linked low 25(OH)D to increased infection risk, not just severity.
Here's the mechanistic bridge to BMI that strengthens your hypothesis: vitamin D deficiency is a major global problem especially among obese children and adults — obesity independently increases deficiency risk, because vitamin D is fat-soluble and gets sequestered in adipose tissue, lowering circulating 25(OH)D. This is the key point — obesity and low vitamin D are not independent; higher adiposity mechanically drives lower serum vitamin D. That makes vitamin D a plausible mediator on the causal path from high BMI to higher infection risk, which is exactly the kind of confound-versus-mechanism question your hypothesis raises.
Two honest caveats on causality, which you'll want to keep in view:
The pre-infection evidence is weaker than the at-diagnosis evidence. One meta-analysis found that the relationship between 25(OH)D status assessed before infection and COVID severity did not reach statistical significance (except 25OHD <75 nmol/L for ICU admission), likely due to few studies and variable time lags between measurement and infection. Most positive findings measure vitamin D at hospital admission, which raises reverse-causality concerns (acute illness lowers 25(OH)D). That said, one review applying Bradford-Hill criteria concluded that reverse causality probably makes a minimal contribution to low vitamin D states in COVID.
Net: your suspected chain — low vitamin D → higher infection risk — is supported observationally, and vitamin D plausibly helps explain the BMI–COVID link rather than competing with it. What the observational data can't yet nail down is how much of the BMI effect runs through vitamin D versus through the other obesity pathways (impaired lung mechanics, chronic inflammation, ACE2/adipokine effects). The RCT evidence needed to settle the causal weight remains the gap.
Related in Vitamin D Life
- Obesity, Hypovitaminosis D, and COVID-19
- COVID-19 hospitalizations: 63% associated with diabetes, obesity, hypertension or heart failure
- Childhood BMI decreased when add a little Vitamin D – meta-analysis
- COVID-19 was the third-leading cause of death in the US, especially in those with dark skin
People with dark skin also have lower levels of Vitamin D