Epidemiology involves the study of determinants of health and the cause of diseases. Health can be analyzed on different levels: the cellular level, the individual level and the population level. Maintenance of good health on a cellular level requires proper nutrition and adequate oxygen supply. Several cells comprise an organ while several organs make up an organ system. However, the body requires only a certain amount of nutrition beyond which, obesity and its related health effects will result. An individual can improve his or her health by doing regular exercises, avoiding smoking, having secure sexual relations, and eating a balanced diet.
The health of a population is affected by several factors that may even be stronger than those that determine individual health. Studies on the causes and prevalence of fatal diseases such as cancer, malaria, and HIV/ AIDS can help determine healthy lifestyles that people can adhere to so as to reduce the prevalence of such diseases. This involves determination of risk factors associated with certain diseases and ways of reducing these risks.
Population health requires the determination of health of the population through self assessed health measurements and also through determination of life expectancy, infant mortality rate. Air pollution, economic growth, smoking rates, dietary habits and literacy levels are other measures of population health. The per capita expenditure of a country on health can also act as an indicator of the level or state of the population health. However, economic inequality is a great challenge even in developed countries, and the poor are more prone to poor health. However, this is not always the case especially in the recent past where the rich and famous are the victims of hard drugs abuse and even many suicide cases.
Provision of basic needs, access to basic health care facilities, social harmony, and focus on early life all promote good population health. Population health epidemiology gathers information through cohort studies, cross sectional studies, multilevel modeling and observational studies of the ecology. International and civil wars also have a profound effect on the population health. The governing authority in any country determines the population health, positively or negatively, through the policies they institute and implement.