I started taking this around 6-7 months ago. Initially I took 10,000 IU a day for the first 2 months, and then backed off to 5,000 IU a day. I had my vitamin D levels tested around a month ago and they came back at 233 nmol/L (93ng/ml). Prior to and while taking the Vitamin D I didn't see much sunlight, so I am absolutely certain that the supplement was doing the job. I've noticed an increased feeling of well-being, clearer and smoother skin, enhanced muscle growth while weight training and fat loss. I'm going to back off to having one every other day to get myself into the target 50-70 ng/ml range.