If one is d3 deficient in presence of mildly elevated calcium less than 10.4, can d3 reduce blood calcium values? what other nutrients can help?

Vitamin D: A calcium of 10.4 or around that is a higher level. If one supplements with D3, or cholecalciferol, this can actually elevate your calcium levels. There are multiple players within this axis including, the parathyroid hormone, calcium , phosphorous, albumin and Vitamin D. Please see your doctor where you can have a full work-up and avoid supplements until doing so.

D3 deficiency : It is good to take some vitamin D supplementation if your level is low, with medical guidance. Correcting your deficiency might raise your serum calcium level. You might have early/borderline hyperparathyroidism.