I found a noticeable difference after taking vit D for six weeks. I was low at the time. Vitamin D is needed for the thyroxin that has entered the cell to connect to the receptors and regulate the cell's metabolism. Therefore, if there is not enough around, you will get sort of low thyroxine-like symptoms.
Unfortunately, it did not turn me into that high-energy wonder woman I aspired to be, but it did take away the can't-be-arsed-with-anything feeling, which was a huge blessing at the time. If I stop taking it, then all my aches and pains come back, particularly around my neck.
It is impossible to get enough from the sun in the winter in this country as the angle of the sun to the atmosphere does not allow the right wavelengths through, so worth taking over the winter. In the summer, you need about 20 minutes exposure a day - so plenty fresh air and exercise will help you store up vit D for the winter. Then lots of sardines, herrings, salmon - Scandi Christmas stuff
