After spending an entire year taking over the counter Vit D faithfully every day, I read the reviews on this product. My lab values went up considerably with in the few months of use. It worked so well to get rid of many of my symptoms ie: Insomnia, body aches, improved my asthma. It's not all the way to with in normal, but my Vitamin D level was in the critical level to begin with. I must worn that it can cause an increase in some symptoms while it is getting in to your bones, in the first few weeks but it's worth it