Vitamin D is a fat-soluble vitamin, which means that you can overdose on it. The 4 vitamins that are fat-soluble are A, D, E, and K. You should always be careful with the doses of these vitamins, so as not to overdo it. Fat-soluble means that the vitamins are stored in your liver and the fatty tissues in your body. It's always wise to check with your doctor or pharmacist about what is the proper dosage of these supplements to take as an individual to reach optimal benefit without doing harm. :-D