Sun. A Biological Input.

We evolved under the sun, not inside walls. The body does not treat sunlight as a luxury. It treats it as a nutrient.

Two Pathways
  • Eyes — morning light into the eyes sets the brain's master clock, drives serotonin production and times cortisol, digestion and sleep. This is the circadian pathway.
  • Skin — UV on skin produces vitamin D and releases nitric oxide. These are separate mechanisms with separate benefits.
What It Does
  • Circadian entrainment — morning light sets the master clock. Miss this window and the whole hormonal timing system drifts — cortisol, digestion, cell repair and sleep all affected.
  • Serotonin — light into the eyes drives serotonin production, which determines mood stability, pain tolerance and sleep quality. Serotonin converts to melatonin at night. No morning sun means degraded sleep.
  • Vitamin D synthesis — UVB on skin converts cholesterol into vitamin D3, a steroid hormone governing bone density, immune function and insulin regulation.
  • Nitric oxide — UVA on skin releases stored nitric oxide, dilating blood vessels and lowering blood pressure. Independent of vitamin D. Cannot be replicated by supplementation.
  • Immune function — sunlight activates white blood cell production and T-cells.
Caveats
  • Avoid sudden extreme exposures. Build tolerance gradually.
  • A clean animal based diet improves sun tolerance — stable cell membranes burn less and tan better.
  • Supplements cannot replicate the full spectrum of sun exposure. They address one pathway. The sun addresses all of them.

PS. Treat the sun as an essential nutrient. Not as nice to have.