依流行病学而言，中风或心脏病常于清晨发作，因此有些学者认为可能是夜间缺乏饮水，造成血液中血球血容上升（即血液浓缩之意），因血液浓缩的关系，使原本具有粥样硬化的血管，更容易产生梗塞，造成中风或心脏病发作。为了证实这个论点，日本科学家做了以下实验：两组病人中 Epidemiologically, stroke or heart attack often occurs in the early morning, so some scholars think it may be a lack of drinking water at night, resulting in an increase in blood hemoglobin (meaning blood concentration). Due to the blood concentration, Atherosclerosis, blood vessels, are more prone to infarction, causing stroke or heart attack. To confirm this argument, Japanese scientists did the following experiment: two groups of patients