I think my low vit D level, taken in early October, was the result of several years of depletion, made worse that year by an Operation in the January. I did not recover from that as well as I would have expected and felt lacklustre all summer and without the mental energy to carry any ideas through to fruition. A naturopath friend was telling me that surgery and general anaesthetic were a big shock to the body and take longer to recover from than you expect. Anyway, after 6 weeks, I suddenly had that
joie de vivre back - not a big revelation - just feeling comfortable with life again, and it was lovely.
Unfortunately, every time I stop taking the vit D, the aches etc come back. I think that in hindsight I may have been bumping the bottom of the VitD levels for some years as I have fair sensitive skin, so took the advice to keep out of the sun too well. I have also read on forums about Vit D that if you have been deficient for some time, then you do need to take it for the longer term - but no real references or research to back this up. It does seem to have been my experience.
A friend with a background in nutrition calculated that you need 3 good portions of oily fish a week (or equivalent) to get the daily rda of vitD from diet (which is considered to be too low these days) and that is quite a lot of sardines on toast! However, her levels are low, in spite of supplements so the GP has put her on a large dose (unfortunately, this is instead of the HRT that she went in and asked for, after going in for meno symptoms over several years
)