Not really "northern hemisphere", but rather northern (and, at least in theory, southern) enough latitudes. The amount UV-B exposure needed for vitamin D synthe

Not really "northern hemisphere", but rather northern (and, at least in theory, southern) enough latitudes. The amount UV-B exposure needed for vitamin D synthesis depends on the season and the latitude, as well as probably cloud cover etc. Anecdotal article I found about latitude vs. UV-B exposure: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037520/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037520/ I live at ~60° of northern latitude, and AFAIK people around here commonly don't get enough UV-B exposure for sufficient vitamin D synthesis for half of the year or so, so you need to get it either from nutrition or supplements.