You can use this https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html to calculate how much to get the recommen

You can use this https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html to calculate how much to get the recommended amount from the Sun which I think is 1000 IU I think 4000 IU is sun burn territory for a single sitting outside. But I only just scanned the website above. I don't know how long it lasts, or if its cumulative, but I heard Vit D is stored in your fat so theres a bit of storage going on. Perhaps therefore, sitting outside in Summer each day during lunch would be enough to get 5000 IU / week.