I found this book fascinating. I can't agree with the premise that the Stuart dynasty's loss of power and the corresponding increase in parliamentary power was primarily caused by the Stuarts' various health problems; however, I've no doubt those health problems did play a significant role. Of primary importance was the failure of Catherine of Braganza to provide Charles II with a legitimate heir and the failure of Mary II and Anne to produce heirs.
One of the reasons I find this book so interesting is that the author, Frederick Holmes, not only has a Master's degree in History, but he is also a medical doctor, a fellow of both the American College of Physicians and the Royal Society of Medicine. Because of this, his diagnoses of the medical conditions of various members of the Stuart family carries more weight. He admits "there is always arrogance in making diagnoses on another physician's patient, particularly at a remove of time." He qualifies his diagnoses as `certain', `possible', `doubtful' and `uncertain meaning'. For example, take William III, who was only a Stuart on his mother's side but was also married to a Stuart. Holmes states a diagnosis of bacterial pneumonia as the cause of William III's death is `certain'. The causes of his failing health before his death--pernicious anemia, hypothyroidism and or sub-acute bacterial endocarditis--are `possible'. There are cases, such as the reason why William and Mary did not have children that cannot be determined from the information available.
I do recommend this book for the information on the practice of medicine in the 17th century and on the health of the Stuart dynasty.The Sickly Stuarts: The Medical Downfall of a Dynasty