Many people are lacking in Vitamin D. I take 50,000 IU once a week (Zahler’s). I felt it made a big difference in my mood after about 6 weeks. Doctor also said “you can’t overdose – you can take 4 pills every Rosh Chodesh – it gets absorbed by the fat, and is used as necessary”.
Our body requires about 4,000 /day. I don’t know where you are located, but most people on the US East Coast above VA are supposedly deficient due to lack of sun exposure. (Religious people are more deficient because we actually wear clothes outside.)