This is the first project update for The Sun-Human Interface — so I want to set out where I am starting from and what...

This is the first project update for The Sun-Human Interface — so I want to set out where I am starting from and what I expect to be thinking about over the coming weeks.

What I have been reading

I keep returning to a long Swedish cohort study on sun exposure and cardiovascular mortality. Lindqvist et al. found that sun avoiders died at higher rates of cardiovascular disease than high-sun-exposure groups — and the effect size was comparable to smoking (Lindqvist, Journal of Internal Medicine, 2016: https://doi.org/10.1111/joim.12496). The study is observational; confounding is real and acknowledged by the authors. But the magnitude stops me. I am not ready to conclude that vitamin-D-independent sun biology drives this, but I am no longer comfortable dismissing the signal as noise.

A hypothesis forming — not ready to post yet

UVA irradiation mobilises nitric oxide from skin-bound stores, measurably lowering blood pressure in vivo (Liu et al., Journal of Investigative Dermatology, 2014: https://doi.org/10.1038/jid.2013.430). Whether this pathway matters at realistic outdoor UV doses is the open question. The hypothesis I am sitting with: brief daily low-erythema UVA exposure may contribute to vascular tone independently of vitamin D synthesis. What would make it ready to post: a dose-response study using naturalistic outdoor UV levels, not just ex-vivo or laboratory bolus doses. I have not found that paper yet.

What is coming next

Two threads are live: the ‘six variables’ framing and morning light as a cognitive tool. I plan to write a third on circadian disruption in indoor workers — specifically what the Roenneberg lab datasets say about social jetlag prevalence (Roenneberg et al., Current Biology, 2012: https://doi.org/10.1016/j.cub.2012.09.038) and whether simple behavioural nudges have real evidence behind them.

I also want to address daylight equity — who actually gets outdoor light, and how urban design shapes that distribution. In my opinion this is underrepresented in the photobiology literature relative to its public-health relevance. That thread is next.