I can say, as an anecdote of one, that I have been taking 5000 IU of D3 along with K2 and Magnesium every day (almost) for about 3-4 years, with no ill effects and what I believe to be a positive effect, in that I have not been ill at all during that time. Cold, flu, anything.
My beginning D3 levels were 39 ng/ml, so just under the ideal range of 40-60, and not really deficient. I have not tested recently, though I believe my numbers would be higher now. I also try to get at least 30 minutes of sun exposure over most of my body 3-4 times per week. Fortunately I live where I can get good sun exposure year-round. Point is, test your serum D3 level and do whatever you need to get into the desired range, and don't take more than that level of supplementation. I do believe that sun exposure is a better choice than supplements, if practicable.
My beginning D3 levels were 39 ng/ml, so just under the ideal range of 40-60, and not really deficient. I have not tested recently, though I believe my numbers would be higher now. I also try to get at least 30 minutes of sun exposure over most of my body 3-4 times per week. Fortunately I live where I can get good sun exposure year-round. Point is, test your serum D3 level and do whatever you need to get into the desired range, and don't take more than that level of supplementation. I do believe that sun exposure is a better choice than supplements, if practicable.