Compared to mice, fruit flies, and other lab animals, humans typically live for the better part of a century. Hence scientific studies of our health are a tricky business, not to even mention the ethics in place around human experimentation: you can’t raise a child in a lab from birth, just as you can’t injure someone just to see what happens.
But modern medicine needs to be based on solid data — so how do researchers get them?
A cohort study
One such way is through what’s called a cohort study. These are prospective studies, meaning they start before any noteworthy events happen (such as death or onset of disease) and track people over time. But because they don’t assign people to “exposure” and “control” groups, cohort studies can’t truly be called experiments — they’re driven more by observation than intervention.
Cohort studies are particularly powerful when conducted over a long period of time; these “longitudinal studies” typically follow a group of people from a young age and track their health and lifestyle over many years.
A longitudinal cohort study can find out if certain aspects of a person’s life – such as smoking, eating a certain diet or a particular family history – are associated with particular diseases or medical conditions. These associations would be impossible to find in the lab.
Dunedin: a remarkable success
One of the most well-known cohort studies, the Dunedin Multidisciplinary Health & Development Study based out of the Queen Mary Hospital in Dunedin, New Zealand, has been running since the mid-1970s and has been regularly collecting near-comprehensive medical data on approximately 1000 people, all of whom are now in their early 40s.
Over 90% of the original cohort is still taking part, which is an incredible achievement for such a long-running study.
The wealth of data that has come out of the Dunedin study is truly incredible, and the research team behind it has published hundreds and hundreds of valuable scientific papers. It has found associations between heavy alcohol use and poor sexual health, as well as poor credit scores and cardiovascular health.
It is also interesting to note associations it hasn’t seen: it found no evidence that the common cat-transmitted parasite Toxoplasma gondii causes behavioural differences in humans, nor that acne causes mental health issues.
The study has borne other fruits, such as providing new ways to measure biological ageing, as well as methods for recording scientific information about the lives of teenagers, both of which should help other researchers doing similar studies.
But the Dunedin study stands out from the pack with its high participant retention rate, very comprehensive data collection methods and ongoing, thorough analysis.
Of course, no single study is satisfactory when looking at something as complex as human health — the more data researchers have, the better informed we can all be about the healthiest ways to live our lives. So for all our sakes, we can hope that longitudinal cohort studies live on into the future.
Want to know more about the Dunedin study? Predict My Future: The Science of Us is available exclusively On Demand at the moment.