Yep, around here it's mostly the early afternoon hours during summer months that the UV levels even rise above the threshold of triggering cholecalciferol synth

Yep, around here it's mostly the early afternoon hours during summer months that the UV levels even rise above the threshold of triggering cholecalciferol synthesis. For many people the summer vacation is pretty much the only time of the year that they have a chance to synthetize vitamin D on their own.