Until 100 years ago the epidemiological scenario of human diseases was concerned with the major killer infectious communicable diseases. In the latter half of the twentieth century there was a progressive decline in infectious communicable diseases and concomitant increase in chronic, degenerative, noncommunicable disease (NCDs). One of the major development challenges in the 21st century is premature death from NCDs. It is estimated that up to 80 per cent of NCDs are preventable by modifying common risk factors including diet and lifestyle. The national strategies in India focus on prevention and health promotion as key to reduce disease burden.
The early decades of twentieth century witnessed a number of wars, famine, natural disasters and the major share of global mortality was contributed by these adverse events and infectious disease epidemics. Infectious diseases include small pox, malaria, tuberculosis, plague, diarrhoea as the major share. Infant and maternal mortality rate were very high and the life expectancy was very short. The socioeconomic and political scenario changed abruptly in the later decades after the world wars. The improvement in standard of living, sanitary awakening, healthy habits and hygiene, nutrition, introduction of antibiotics and immunization has hastened the decline of infectious diseases and premature mortality rates1 . There was a rapid decline in the maternal and infant mortality rates and a marked advancement in life expectancy which was associated with the marked change in disease patterns.
Recent studies have shown that few cells live as long as the individual they belong to without renewal. A majority, if not all, the cells making up the cerebral cortex belong to this small group. The life span of some other human cells are as follows:
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