Location and vitamin D synthesis: is the hypothesis validated by geophysical data?

Area of Science:

• Environmental Science
• Public Health
• Dermatology

Background:

• UV exposure is linked to disease latitude gradients.
• Emerging evidence suggests UV's protective role in various cancers, autoimmune diseases, and mental health conditions.
• Vitamin D synthesis is primarily driven by UV radiation.

Purpose of the Study:

• To measure and compare vitamin D producing UV and erythemal UV levels across the USA.
• To challenge existing beliefs on the latitudinal dependence of vitamin D UV.
• To inform public health recommendations regarding UV exposure and vitamin D synthesis.

Main Methods:

• Utilized US EPA's Brewer Spectrophotometer network for high-accuracy UV measurements at seven US locations.
• Compared vitamin D UV (derived from previtamin D action spectrum) with erythemal UV.
• Employed computer modeling to generalize findings for latitudes 0-70 degrees N.

Main Results:

• No significant latitude gradient in vitamin D UV relative to erythemal UV was observed from March to October across all sites (18-44 degrees N).
• During cooler months (November-February), latitude significantly impacts vitamin D UV, with levels decreasing dramatically at higher latitudes.
• Low latitude locations (<25 degrees N) exhibit consistent wintertime vitamin D UV levels comparable to summer levels.

Conclusions:

• The assumption of significant vitamin D level latitude gradients throughout the year may be incorrect for large parts of the USA.
• Public health messaging on increasing UV exposure during winter is irrelevant for lower latitudes and may lead to overexposure.
• Findings necessitate a re-evaluation of UV exposure guidelines and disease research considering seasonal and latitudinal variations in vitamin D UV.