Depends on the definition of reasonable. D3 is fat soluble and if you take too much for years it can accumulate too much in your body. I'd say 2,500 IU is max

Depends on the definition of reasonable. D3 is fat soluble and if you take too much for years it can accumulate too much in your body. I'd say 2,500 IU is max to take daily without infrequent blood tests to calibrate the optimum.