I started taking Nature Made Vit. D 1000 last year. After taking it only several months I saw my doctor for routine blood work. When the doctor saw the results of my blood work she said I had the highest levels of Vit. D in my blood that she's ever seen and said it was fantastic. She was really surprised. I have since read that a study was made of about 55 different brands of Vit. D 1000 I.U. and all of them EXCEPT Nature Made had less than 1000 I.U. Nature Made was the only brand that had the correct amount. Because so many brands were tested you can be sure that many of them are the most popular and well known brands. Considering the results of my blood work, I'm not surprised that Nature Made is what the label says it is. Nature Made is supposed to be highly recommended by pharmacists and I can see why. Coupons are often available online for Nature Made so you can often save money on your purchase. I highly recommend this product.