worldwide

@chl if vitamin d deficiency were indeed one of the main drivers of the #covid19 pandemic, what would we see? a gedankenexperiment …

@chl (some basics: [most] vitamin d in humans is generated when a component of sunlight [uv-b] hits the skin; only little uv-b reaches the ground in winter; very few good food sources; supplementation is easy & cheap, but not entirely w/o perils; melanin & skin age reduce synthesis)

@chl the pandemic would start in the northern hemisphere in late winter, when vitamin d levels are lowest

@chl regions near the equator would remain relatively (maybe surprisingly?) less affected (and any peaks would be less pronounced), despite their (by western standards/arrogance) “poor” healthcare systems (the same being clearly visible in seasonal influenza charts)

@chl regions w/ high levels of air pollution and people with low vitamin d levels (the elderly, [many?] dark-skinned people living at high latitudes [northern europe, north america]) would be disproportionately affected

@chl (so far, those were [laughably] easy predictions/retrodictions, as all of this has happened already)

@chl pandemic activity in the southern hemisphere would pick up 6 months after the north (i.e. by july/august); luckily, the (far) south is much less densely populated than the north & the tropics and there’s now ample warning