We know that sunlight is vital for children's healthy bone development.


Russian children in Siberia are bathed in ultraviolet lamp during the winter; and, I recall my mother in the tropics sitting us children for a spell of morning sunshine.
But we would be mistaken to only attribute the creation of Vitamin D3 in the skin as the sun's only benefit & therefore think that cod liver oil or a vitamin D3/K2 supplement can substitute for solar radiation properly received. [n.b., There are many good health reasons for supplementing with cold-pressed, wild-caught cod liver oil beyond this current discussion.]
41 kya, during the Laschamp event, when a shift in the Earth's geomagnetic fields reduced the protective shielding that reduces the sun's intensity, it is speculated that modern humans survived by seeking refuge in caves, slathering ochre on the skin and sewing protective clothing (advantages Neanderthals might not have shared.)
But today, we have paradoxical evidence that low sunlight exposure appears to result in a greater number of internal cancers and that non-sunburn skin exposure does not increase melanoma risk. In the past two decades, there's also been a lot of research on circadian mechanisms and the biochemistry of sunlight interacting with human bodies. We might be close to the truth in saying that "humans are plants with motion & emotion."


Since we're on a six-months of travel & I don't have my Endnote bibliography with me, I decided to chat with Claude Anthropic 4.0 for a quick literature review. I posed a detailed question & requested the mechanisms and health implications of sunlight exposure without sunburn. He provided an excellent, but, I felt, dated overview of the risk/benefits of appropriate sun exposure, so I commented:
"I'm surprised that daytime mitochondrial melatonin production for ROS modulation wasn't mentioned; or that there was no mention of the higher correlation of melanoma with higher latitudes or lower sun exposure."
Claude quickly responded:
"You're absolutely right, and thank you for pointing out these crucial gaps. Both points represent important paradigm shifts in our understanding."
(To be continued with Claude’s summary of the health benefits of using sunlight without sunburn.)