Vitamin D and skin physiology: a D-lightful story.
Level 5 - mechanism / opinion, no new human data
Narrative review and physiological overview of cutaneous vitamin D synthesis
PubMed 18290718 · doi:10.1359/jbmr.07s211
What was done
The author summarizes the photobiology and skin synthesis of vitamin D3, reviewing how solar UVB (290–315 nm) converts 7-dehydrocholesterol to previtamin D3. The review details the impact of latitude, altitude (from 169 m to 5,300 m), season, skin pigmentation, sunscreen, and clothing on synthesis, and compares dermal production with dietary sources.
What was found
Previtamin D3 synthesis is minimal during winter at latitudes above ~35°. In November at 27°N, synthesis was ~0.5% at 169 m (Agra) and 1,400 m (Katmandu), increasing ~2-fold at ~3,400 m and ~4-fold at 5,300 m (Everest base camp). Whole-body exposure in a bathing suit to 1 minimal erythemal dose (MED) is estimated to equal ingesting 10,000 to 25,000 IU of vitamin D. Wild-caught salmon had 75% to 90% more vitamin D3 compared with farmed salmon.
Why it matters
It outlines the environmental and biological determinants of cutaneous vitamin D production, explaining the physiological basis of seasonal deficiency across different latitudes.
Limits
The abstract describes a broad narrative review rather than a single systematic trial. It does not provide sample sizes, participant demographics, variance measures, or formal statistical hypothesis testing for the reported observations.
Cited by
- supports Living above the 35th parallel prevents sufficient atmospheric penetration of UVB radiation to synthesize adequate vitamin D in the skin during winter months.