After being diagnosed with subclinical hypothyroidism and some subsequent fertility issues, it was found that my vitamin D was very, very low. I started taking 5000-8000 iu daily and within 4 weeks, my vitamin d levels were up to a normal level and my TSH was down to a more normal range. My symptoms lessened and I had more energy. My husband calls it my liquid sunshine.
Also- I am a very fair skinned person so normally I burn in the sun but ever since I started taking vitamin d tinctures, I haven’t gotten burned once and have even gotten a nice tan! Not sure if that’s related but thought it was pretty neat.