In the next two decades there will be dramatic changes and transitions in the world's health needs, as a result of epidemiological transition. At present, lifestyle and behaviour are linked to 20-25% of the global burden of disease. This proportion is rapidly increasing in poorer countries. In the developing regions, where four-fifths of the planet's people live, noncommunicable diseases such as depression and heart disease, as well as road traffic deaths, are fast replacing the traditional enemies such as infectious diseases and malnutrition, as the leading causes of disability and premature death. By the year 2020, noncommunicable diseases are expected to account for seven out of every ten deaths in the developing regions, compared with less than half today. Injuries, both unintentional and intentional, are also growing in importance and by 2020 could rival infectious diseases as a source of ill-health.
It was previously thought that, as countries develop, noncommunicable disease replaced communicable disease as the main source of ill-health. However, there is now evidence that the poorest in developing countries face a triple burden of communicable disease, noncommunicable disease and socio-behavioural illness. The global burden of disease methodology shows that the epidemiological transition is already well advanced, suggesting that public health policy in poor countries, with its traditional emphasis on infectious disease, will need to adapt.
Three examples of health transition are:
- The burden of mental illnesses, such as depression, alcohol dependence and schizophrenia, has been seriously underestimated by traditional approaches that take account only of deaths and not of disability.
- Adults under 70 years of age in sub-Saharan Africa today face a higher probability of death from a noncommunicable disease than adults of the same age in established market economies.
- By 2020 tobacco is expected to kill more people than any single disease, even HIV/AIDS.
Demographic transition refers to a change in birth and death rates. As countries develop, they move through various stages of demographic transition: from virtually stagnant rates (high birth and death rates) to rapid growth (high birth rates, low death rates) and then to a stable low growth rate when both births and deaths are low.