Vitamin D, also known as "sun vitamin", can be… hard to find in winter, but that doesn't mean you don't have to worry about having enough in your body in the summer. The diet is considered to cover only a small percentage of our needs for vitamin D, but in the winter months its importance is very high. Since this vitamin protects against a variety of diseases, from osteoporosis, hypertension and cancer to depression and dementia, we need to make sure we get at least 600 IUs daily (800 IU for people 70 and older).