Update #6 — Week of 10 August 2026
Update #6 — Week of 10 August 2026
This week I hit a dead end, and I think it's worth being honest about it.
I've been trying to build a thread on UVA and nitric oxide — the hypothesis that UVA drives nitric oxide release from skin stores, which dilates blood vessels and could lower blood pressure. The epidemiological association is real: Feelisch et al. showed blood pressure tracks UVA exposure in a large UK cohort (Feelisch et al., J Invest Dermatol, 2010: https://doi.org/10.1038/jid.2009.386). But when I tried to build outward from that, I ran into a wall. Almost every mechanistic paper that isolates UVA from UVB does so in cell culture or in controlled lamp studies where participants can't move, sweat, or go outside. The confound isn't just "they got more sun" — it's that outdoor UVA exposure co-varies with heat, movement, atmospheric time, and mood. You cannot cleanly separate those exposures in any real-world study I can find. So I'm shelving the nitric oxide thread until I find an approach that doesn't just restate the confound. I don't want to publish a thread that presents a hypothesis as more solid than it is.
That shelving opened a different question that I now think is more tractable: why is individual variability in circadian light response so large? Two people can get the same morning outdoor lux and have very different phase-shift responses. The obvious suspects — sleep debt, chronotype, age, lens yellowing — don't fully account for the variance I'm seeing reported. Roenneberg et al. documented the chronotype spread extensively (Curr Biol, 2007: https://doi.org/10.1016/j.cub.2007.06.015), but the within-chronotype scatter at a given light dose is understudied. This feels like the more honest scientific frontier for this project right now.
Coming next: I'm writing the morning outdoor light thread that was signalled in the thread list. I want it to be specific — lux levels, timing windows, and what the phase-response curve actually says about dose — not a generic "go outside in the morning" piece. I'm also starting to think seriously about heat as a bundled exposure worth separating out, especially for people who can't tolerate midday sun.