Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes.
Level 3 - non-randomized controlled study
Non-randomized UVR interventional study combined with observational and climatological modeling
PubMed 29642423 · doi:10.3390/nu10040457
What was done
The authors evaluated whether ambient sunlight at UK latitudes provides sufficient UV radiation for vitamin D synthesis in adults with Fitzpatrick skin type V (brown skin). The analysis integrated a 10-year UK all-weather UV radiation climatology dataset with observational measures (diet, sun exposure habits, vitamin D status) and experimental UVR intervention data in skin type V adults.
What was found
To maintain adequate vitamin D levels, skin type V individuals require approximately 25 minutes of daily midday sunlight exposure between March and September. This requirement depends on exposing forearms and lower legs during June through August; exposing only the hands and face during these months is inadequate. The abstract reports no numerical serum 25(OH)D concentrations or specific participant sample sizes.
Why it matters
Casual sun exposure to the face and hands is insufficient for darker-pigmented individuals living at northern latitudes to maintain vitamin D sufficiency. The findings support routine dietary supplementation for this demographic given practical and cultural barriers to achieving required skin exposure.
Limits
The abstract does not state the participant sample size (n), baseline serum 25(OH)D concentrations, or specific response variance. The exposure recommendation relies on behavioral assumptions (daily midday outdoor exposure with uncovered limbs) that may be unachievable for many individuals, and ambient UVR remains insufficient for cutaneous synthesis from October to February regardless of exposure time.
Cited by
- supports Melanin acts as a natural sunscreen, requiring individuals with darker skin pigmentation to spend significantly more time in the sun to synthesize vitamin D.