I haven't researched any answers, but I did hear from Oprah's Dr. Oz, that Vitamin pills should be cut in half because the vitamins don't get absorbed in a whole tablet.
I cut mine in half and and take 1/2 in am and 1/2 in pm.
I take 500 mg Calcium with D twice a day.
I also take fish oil 1000 mg capsules for the Omega3 cholesterol lowering effect..