This is a very informational popular science book demonstrating the link between vitamin D deficiency and multiple health problem and disorders, including autism.
The book is very well written and easy to understand. The explanations are simple and the glossary in the book of the book is helpful. Cannell does a good job of showing how important it is to get adequate sun exposure without damaging the skin and making one more susceptible to skin cancers. He also touches on food tolerance issues, which many children with ASD have, and suggests ways to ensure they are getting enough vitamin D (as well as suggestions for vegetarians and vegans to get vitamin D).
I also like that this book includes some alternative theories regarding the causes of autism and how vitamin D relates to them. The information provided in the book is thorough, yet easy to comprehend.
Cannell is cautious with his advice, saying that it is not a cure, and constantly reminds parents to test their children's vitamin D levels using blood tests to ensure the safety of the treatment. While Cannell admits that conclusive research and testing may take years more to complete, he does a risk/benefit analysis to show that the treatment is harmless and could be tried as long as blood tests are done frequently.
This book is a good summary of the current research on vitamin D and provides information on a possible treatment for many disorders such as autism.