I must admit at the start of this note that I thought I understood the definition of lifestyle diseases -- in my mind, the term referred to diseases caused by some action, or lack of action, on the part of an individual that caused a disease to develop. Examples of the former, an action taken, would be lung cancer caused by smoking or hepatic cirrhosis caused by excessive ethanol intake. It turns out that I was wrong in my use of the term. The causes of lifestyle diseases are based on the general behavior of populations rather than individuals. Here is the definition from the Wikipedia:
Lifestyle diseases (also called diseases of longevity or diseases of civilization) are diseases that appear to increase in frequency as countries become more industrialized and people live longer. They include Alzheimer's disease, atherosclerosis, asthma, cancer, chronic liver disease or cirrhosis, Chronic Obstructive Pulmonary Disease, Type 2 diabetes, heart disease, nephritis or chronic renal failure, osteoporosis, acne, stroke, depression and obesity.
The reason I was thinking about this topic was that a recent article had caught my attention (see: Molecular imaging that will bring about a revolution in diagnosis and drug discovery). Its categorization of cancer, dementia, and diabetes as lifestyle diseases makes perfect sense now that I understand the correct definition for lifestyle disease (boldface emphasis mine):
Molecular imaging is essential for a better understanding of life, because phenomena in living beings result from interactions between molecules. Masaaki Suzuki, of the Molecular Probe and Drug Design Laboratory, says, “Molecular imaging is the ultimate goal of life science.” Molecular imaging is expected to help in the detection of lifestyle-related diseases, such as cancer, dementia, and diabetes, at an early stage, as well as in developing good new drugs with the fewest side-effects far more quickly.
Taking the example of cancer as a lifestyle disease, I do understand the idea that a longer life free of, say, infectious diseases, may increase the risk of developing cancer for an individual. Hence the notion that lifestyle diseases being synonymous with diseases of longevity. I also understand that living in an industrialized nation could increase one's exposure to pollutants or food additives that might be carcinogenic. However, I also suspect that some individuals are genetically predisposed to developing malignant neoplasms, partly as a result of having a less efficient or effective DNA repair mechanism, allowing more rogue cells to develop and proliferate. Here's an interesting little article on cancer immunology that includes a reference to the cancer immunosurveillance theory.