 Pigmentation increases the heat load in hot climates, and dark-skinned people absorb 30% more heat from sunlight than do very light-skinned people, although this factor may be offset by more profuse sweating.In cold climates dark skin entails more heat loss by radiation.Pigmentation also hinders synthesis of vitamin D, so that in areas of poor nutrition darker skinned children are more liable to rickets than lighter skinned children.