I know this because I was a part of the first longitudinal study in the world to show the connection between a low GI diet and serious eye disease.

The study, known as the Blue Mountains Eye Study, has been following the eye health of older people in the Blue Mountains at regular intervals since 1992. It is a cohort study which has contributed significantly to our understanding of the lifestyle factors that may prevent, or cause, serious eye disease.

A cohort study looks at a population group, usually over a significant period of time, and gathers information about lifestyle and health outcomes. It follows the regular habits of individuals at specific intervals and analyses how those habits may have affected the participants’ health outcomes.

For example, the Blue Mountains Eye Study also found that people who eat fish once to twice a week are much less likely to develop macular degeneration. We can say this with confidence because we have information about the diets of people in the study and were able to compare the dietary differences between those who had, or had developed, eye disease and those who did not.

Another successful and well-known cohort study is the Dunedin Multidisciplinary Health and Development Study. It began studying a group of more than 1000 babies at birth between 1972 and 1973. These individuals have been followed at regular intervals ever since.

There have been hundreds of research publications detailing findings from this study. One of the most recent looked at young children’s self-control skills — such as self-discipline and perseverance — which predicted their health, wealth and criminal history in later life, regardless of IQ or social background.

These are just a few examples of the value of cohort studies, which provide us with a great deal of information about how our lifestyle affects our life outcomes. Yet there are a number of factors that are critical to successful cohort studies such as these.