Approximately 80 percent of the population is deficient in vitamin D. Low vitamin D level is associated with cognitive decline, and is required for maintaining brain synapses. Normal vitamin D blood levels should be from 50 ? 100 ng/ml for serum 25-hydroxyvitamin D which is the active form of vitamin D in your body. If you are trying to lose weight optimal vitamin D is imperative to control leptin a hunger blocking hormone. While vitamin D3 is recognized for its role in calcium absorption and metabolism, it is vitamin K2 that directs calcium to bones rather than joint spaces and arteries. Take Protocol 5000 mg per day of D3 with 180 mcg per day of K2