As many people don't realize, your body only needs 10 - 20 minutes of sunshine per day to provide the RDA of Vitamin D. However, most of us don't get that, or some may require more that the RDA for medical reasons. Nevertheless, because Vitamin D is FAT soluble (a toxic compound), it can be toxic and have harmful effects to the body when taken in excess. One effect is that toxicity can lead to hypercalcemia (excess of calcium in the blood), which can incur nausea, weakness, vomiting, and commonly frequent urination. And such symptoms can progress to bone-related issues as well as renal issues, like Kidney stones. Those are not fun to pass! Prior to taking any fat-soluble nutritional supplements, like Vitamin D, you should have your blood tested for 25-OH. Surprisingly, once tested for the first time, most people are on the low side of normal, or deficient. But, if you are taking Vitamin D, it's important to let your doctor know how much of it you're taking. Your blood must be routinely tested. Also note that Calcium needs to be taken with Vitamin K and D3 in order to put the Calcium into the bones. If Calcium isn't taken with the Vitamin K and D3, the Calcium will go into the blood stream, which defeats the purpose of taking it for your bones. Again, this NatureWise D3 5,000 IU is a very good product "if 5,000 IU's are needed", but mega doses as such (taken all at once) can incur such medical issues as indicated above. I only take 2,000 IU of Vitamin D3 in the evening with my Calcium and Vitamin K. While speaking of Calcium, it's imperative that Calcium never be taken within 6 hours of any Thyroid medication