Years ago I was on 1600 mg calcium supplements from a big box store and my calcium levels didn't improve. I changed to Wonderlabs and within 3 months, my calcium levels improved so much that I could reduce amount taken down to 400mgs. Now, all my supplements come from Wonderlabs. I have an autoimmune disease and have to watch Vit D and B as well. Wonderlabs Vit D and B work great at keeping my levels in the correct range. I highly recomment Wonderlabs.