I've learn't how to put PDF files online so I've put a copy of
How to Optimize Vitamin D Supplementation to Prevent Cancer, Based on Cellular Adaptation and Hydroxylase Enzymology REINHOLD VIETH
So you can all read it and look at the diagrams I think you will also be able to download it from that link as well. It's an important hypothesis as it explains why it is better to use daily, weekly supplements rather than rely on large doses at extended intervals.
While I don't want to put anyone off having a winter sun holiday in the tropics I think anyone considering doing this would be best advise to take a higher level of vitamin D3 before they go (rather than think I'm going to get plenty of sun next month so no need to supplement now) NOT TO USE any D3 supplements while they are on holiday (to avoid very high levels) and then to resume supplmenting on the last day of the holiday and continue using effective amounts when you get home.
This is to try to even out the level over the period.
Try to keep 25(OH)D level stable will prevent the need for fine tuning of the immune system and shorten the time where there is imbalance between activating (25- and 1a-hydroxylase) and the metabolizing (24-hydroxylase) enzymes.