The effects of environmental and lifestyle factors on blood pressure and the intermediary role of the sympathetic nervous system.

Essential hypertension is thought to be caused by both genetic and environmental factors, with varying combinations in different individuals. Proposed environmental factors include exposure to chronic stress, obesity alcohol and salt intake, and physical inactivity. The prevalence of hypertension is related to social factors such as urbanization and education. Several studies, conducted both experimentally in animals and observationally in people, have suggested that chronic social conflict is associated with higher blood pressure. Ambulatory monitoring has shown that most people have their highest pressures during working hours. Occupational stress can be evaluated as job strain, which is a combination of high demands at work with low decision latitude or control. Job strain has been related to coronary heart disease, and a number of studies have shown that it is also associated with higher ambulatory blood pressures, both cross-sectionally and prospectively, in men but not in women. It is likely that environmental and lifestyle facts operate interactively rather than independently to promote hypertension. There is also extensive evidence that overactivity of the sympathetic nervous system plays a role in the development of hypertension, particularly in its early stages. So far it has not been established why this should occur. There are several possible environmental origins, however, and all of the lifestyle factors mentioned above have been shown in at least some studies to operate via the sympathetic nervous system.