The Shadow Rule – you make more Vitamin D when you are taller than your shadow – 1992

Grassroots Health Oct 2015 email

“A general rule of thumb?
When you are taller than your shadow, your body is able to make vitamin D”

Atmospheric sun protection factor on clear days: its observed dependence on solar zenith angle and its relevance to the shadow rule for sun protection 1992

The shadow rule: a simple method for sun protection. 1998

“Thus, when a person's shadow is shorter than the person is tall, the intensity of UVR from the sun is more likely to cause sunburn.”

Actually: Generate about 1/2 as much vitamin D when shadow is as long as you are tall

Example of how much Vitamin D can be generated at 23 degrees latitude in the summer
Shaded areas are when the shadow is longer than the person
Lots of good Vitamin D in the morning - before it gets too hot

from: Sun-induced production of vitamin D3 throughout 1 year in tropical and subtropical regions: relationship with latitude, cloudiness, UV-B exposure and solar zenith angle - 2021- Which is behind a paywall - https://doi.org/10.1007/s43630-021-00015-z

Similar latitudes for which the sun is directly overhead: Sao Paulo, Florida Keys, Hong Kong, Mumbai

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See also VitaminDWiki

No – 10 minutes per day of sun-UVB is NOT enough
Optimize vitamin D from the sun
5 Amazing Properties of Sunlight You've Never Heard About
Overview Suntan, melanoma and vitamin D
Overview UV and vitamin D
Vitamin D vs angle of the sun

Morning sun?

Boost Your Winter Mood and Productivity with vitamin D or morning light
Health benefits of the sun - more than just at noon
The Healing Sun –1999 book highlights at VitaminDWiki
  Sunbathe for Tubercoulous only 6-9 AM – not in middle of the day – pg , 119

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