Optimal vitamin D3 daily intake of 2000 IU inferred from modeled solar exposure of ancestral humans in Northern Tanzania

•Duration of sunbathing for adequate vitamin D level is derived from the Hadza life style.•A novel formula to calculate optimal solar exposure to get vitamin D is proposed.•Daily oral supplementation of 2000 IU of vitamin D3 is recommended for in-door workers.

Recently, high serum 25-hydroxyvitamin D concentration (~ 110 nmol/L) was found in the Hadza tribe still keeping ancient hunter-gather life style. This level could serve as optimal vitamin D level that was built during millennia of human evolution. The personal vitamin D3 effective solar exposures of the Hadza adults are estimated using radiative model simulations with input from the satellite observations over lake Eyasi (3.7°S, 35.0°E). The calculations are carried out assuming the Hadza typical clothing habits and specific scenarios of the out-door activity comprising early morning and late afternoon working time in sun and prolonged midday siesta in the shade. The modeled doses received by the Hadza are converted to the vitamin D3 effective daily doses pertaining to the lighter skinned persons. We propose a novel formula to get adequate vitamin D level — exposure of 1/3 MED around local noon to 1/3 part of the whole body during warm sub-period of the year in the low- and mid-latitude regions. Such daily solar exposure is equivalent to ~ 2000 IU of vitamin D3 taken orally. For many contemporary humans with limited out-door activity habit achieving such daily norm requires vitamin D3 supplementation of 2000 IU throughout the whole year.