Those familiar with evolution theory know that humans are adapted or genetically designed for conditions as they existed in prehistoric times, say 10,000 years ago. It is now widely accepted that many current human ailments result from the major differences that exist between the environment and general situation in which we now live and conditions in the distant past. Our bodies struggle to cope with the current conditions because they were designed for the earlier time.

Bowles makes a fascinating and, in my opinion, scientifically valid case that vitamin D is part of just such an adaptation issue. The skin makes vitamin D (actually a hormone) in response to exposure to sunlight. The hormone, as they usually do, signals other biological systems that would in prehistoric times want to vary between winter and summer. Bowles suggests that scares regarding skin cancer caused people to protect against sun exposure and consequently caused their bodies to falsely adjust to prehistoric winter conditions. Development of sun screens worsened this situation. He further suggests that obesity, depression, and many other conditions are therefore caused or worsened by tricking the body into thinking it is perpetually winter.

Bowles goes on to describe his personal odyssey and how he experienced miraculous improvement in various medical conditions after taking more than the recommended dose of vitamin D.