Is it or isn't it vitamin D? 7. April 2010 William Davis (63) Jackie takes 10,000 units of vitamin D(3) per day as a gelcap.Her starting 25-hydroxy vitamin D blood level was 18.1 ng/ml. Severe deficiency, no surprise. On her 10,000 units per day, Vitamin Shoppe brand, her 25-hydroxy vitamin D level was 76.2 ng/ml--perfect. It stayed in this range for about two years. She then changed to the Nature Made brand gelcaps she picked up at Walgreen's. Repeat 25-hydroxy vitamin D level: 23 ng/ml. This has now happened with five different people, all taking the Nature Made brand. If you are taking this brand of vitamin D, please be on the alert. You might consider a 25-hydroxy vitamin D blood level to be sure it actually has the vitamin D it's supposed to have. Or, change brands.