The group https://grassrootshealth.org https://grassrootshealth.org sells an inexpensive at-home test kit for D3 serum levels. IIRC it includes two tests so tha

The group https://grassrootshealth.org https://grassrootshealth.org sells an inexpensive at-home test kit for D3 serum levels. IIRC it includes two tests so that you can make changes if needed then check to see how much they helped, and back off on supplements if desired. I had also been taking 5000 IU/day with K2, which helped me get up to 50 ng (starting from 39). I stopped taking the supplements because I felt sun exposure was probably the better way to approach it. For one thing I live in a sunny place, and I enjoy the relaxation. Also, my guess is that D3 levels may be a proxy for things like sun exposure, and that the health benefits might derive from those instead, and might be more complex than just one compound. If I can't reliably get sun exposure though, as in the next three months when my local UV index gets pretty low, I'll go back to supplementation.