I encourage everyone to read http://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/.
Once you read it if you decide your diet has enough of these co-factor’s, then you have nothing to worry about.
Many diets now a days do not contain enough magnesium and Vitamin D uses a lot of it. (This is why people sometimes get symptoms once they start taking Vitamin D.)
Now you take 2000iu and “feel great” but do you know what “level” that gets you too? I only ask because at levels below 40ng/ml and your risk for cancer and autoimmune diseases rises “dramatically”. I am not being overly dramatic, this is what scientific studies show.