Changing causes of death
Internationally, deaths caused by infections such as measles, smallpox and tuberculosis have declined and deaths caused by conditions associated with ageing or lifestyle, such as heart disease and lung cancer, have increased. This change in the types of diseases that cause death is called ‘the epidemiological transition’. It is usually accompanied by a reduction in childhood deaths and an increase in how long people live.
Like most societies across the world, New Zealand has experienced this shift in disease and death patterns. Over time, diseases of old age and lifestyle have replaced infections as the main types of sickness and primary causes of death.
New Zealand has had two major epidemiological transitions. For non-Māori the transition occurred very early, in the 19th century. For Māori, the transition happened much later, in the 20th century.
Life expectancy trends
Epidemiological transition resulted in radical improvements in longevity. Some universal trends in life expectancy are seen in all epidemiological transitions.
- In populations with very high mortality, some people survive to very old age, even if the majority die in childhood. For this reason, it is wrong to interpret low life expectancy as meaning that nobody lives beyond, say, 30 years.
- When mortality is high and most people die at young ages, the small number of people who survive to adulthood may, simply as a result of living longer, acquire a higher life expectancy than they had at birth.
- There is an upward shift in the age at which people die – from childhood, to middle age, and then eventually to older age groups. The shift is often initiated by a decline in the infectious diseases that mainly affect children.
Increase in life expectancy is one of the most significant historical developments to have occurred worldwide since the second half of the 18th century. Life expectancy then was 20–35 years. By the early 21st century it had nearly tripled, to 60–80 years and more.
Women’s and men’s life expectancy
In New Zealand in the 21st century the life expectancy of women is higher than that of men. In the past, men’s life expectancy could exceed that of women, notably during women’s childbearing years. This is common in societies with both high mortality and high fertility, and was particularly noticeable in Pākehā settler society in the 1870s and Māori society in the 1940s. It has been suggested that poorer female survival during the reproductive years is due to the physiological burden of childbearing. This weakens women so they die not only from complications of pregnancy and labour, but from other causes, notably tuberculosis.