This book is excellent. After reading this book I've started taking vit d3 also. My dosage for two months have been 30000 units a day. I had a hip pointer injury from martial arts. After a year of pain, after two monhs I am pain free! Both my shoulders were dislocated in the military 25 years ago. I've had weakness and some pain in them for years. After three months my bench press has improved ten percent after having plateaued for years.i increased my intake to 50000 units a day now for two more months. My family in that time frame has caught colds and the flu but I have been free of illness. My energy level also has been up. I have even lost a few pounds with out any significant changes to my diet or exercise regime. I have a masters degree in nutrition from university of Illinois and I find the premise of this book intriguing! This is a great book, I highly recommend it!