University of Oulu, 2017

Unique population survey throws light on disease risk factors

University of Oulu carries out birth cohort studies, which are rare and valued on an international scale. In this project, babies born in Northern Finland in 1966, 1985 and 1986 have been studied extensively already in the mother's womb and approximately every 10 years thereafter. Scientists have used this enormous research material to study a number of different diseases. The results have been applied to, for instance, Current Care Guidelines and prevention of illnesses.

Medical history was being made in Oulu in the 1960s, when Paediatrician Paula Rantakallio became concerned about the high morbidity and mortality of mothers and newborn babies. On her initiative, an extensive health examination was performed on all babies born in the Province of Oulu and Lappi in 1966, and their mothers. The objective was to search for causes of newborn morbidity and mortality, and ways to improve the situation.

As many as 96% of babies born in 1966 were examined. The same persons have since been examined every 10 to 15 years, most recently when they were 46 years old. A similar process was started among babies born in 1985 and 1986.

Taking up to two days at a time, these examinations have included various laboratory tests and imaging studies. In addition, the participants’ health has been studied through various surveys. Information from national registers regarding, for instance, the use of medicinal products, has also been attached to the material.

This research has created an enormous amount of material which provides an endless source for scientists. A myriad of back, eye and skin disease studies have been conducted on the basis of this material, as well as research in the field of dentistry, gynaecology, occupational health, and so on. The material has been used for, for example, diabetes research.

Public health improves

Professor Jouko Miettunen emphasises that an extensive cohort study conducted on an entire age group provides reliable information:

“The cause and effect relationships of diseases are otherwise difficult to study, but in a birth cohort study, this is considerably easier. In a clinical study, we depend on, for example, what a child's mother says during the appointment. Information received in this manner can be distorted. Information generated by a cohort study is reliable, and we have access to comparative data about the entire population.”

It is difficult to find similarly extensive cohort studies in the world:

“Both cohorts are exceptionally good in size and duration. England has two older cohorts, which serve as role models for our cohort studies, but other similar studies are newer and more limited.”

The term ‘cohort’ was borrowed into medical research from ancient Rome, where cohort referred to a military group formed by soldiers. In this birth cohort study, the cohort, i.e. group of study subjects, consists of persons born in Northern Finland during the specific years.

Over 1300 studies in different fields in Finland and abroad have been published on the research material of birth cohorts. At a general level, one of the most important results is this scientific information’s influence on public health, says Academy Research Fellow Erika Jääskeläinen. The cohort material has provided useful information for medical textbooks and Current Care Guidelines, among others.

Even cigarettes increase the risk of psychosis

Miettunen and Jääskeläinen use the cohort material for their psychosis research. The material has spawned a variety of results. In particular, the forecast and risk factors of schizophrenia have been studied extensively.

“Studies on medication are the most interesting ones,” Jääskeläinen says.

“In particular, large doses of antipsychotic medication are associated with the decline of verbal memory and learning, as well as changes in the brain, as presented by the monitoring of schizophrenia over the period of nine years.”

The researchers point out that potential confounding factors cannot be ruled out, in other words, it is not possible to say that antipsychotic medicines are the cause for such changes in the brain. Medication in large doses may, however, be at least one factor explaining the cognitive decline and loss of grey matter in the brain as observed in the patients. In addition, antipsychotic drugs may increase the risk of diabetes and patients’ weight.

“Antipsychotic medicines support the treatment of schizophrenia, but they also have adverse effects. The medicines help manage the symptoms, for instance, and reduce mortality. Our research will help determine the risk/benefit balance,” Jääskeläinen says.

One of the results obtained from the material is linked with the connection of drugs and psychosis. Miettunen refers to Antti Mustonen's doctoral dissertation work completed in 2018:

“According to this doctoral dissertation, intoxicants, cannabis, smoking, and inhaled drugs double or triple the risk of psychosis,” Miettunen says.

Psychosis affects young people in particular

According to the cohort study, psychosis occurs most frequently among 30-year-old persons, while people fall ill with depression and anxiety also at an older age. Depression and anxiety seem to be associated with low-grade inflammation.

“Genetics also play a role in the background of psychiatric disorders. Genes associated with an increased risk of psychiatric disorders have been identified on the basis of the cohort-66 material,” Jääskeläinen says.

A significantly larger number of persons born in 1985 or 1986 than persons born in 1966 experienced psychosis by the age of 27. Miettunen does not know whether psychosis has become more common. He thinks that the so-called mood psychoses may now be identified better than earlier.

Brain imaging research has also been conducted on the persons born in 1985 and 1986.

“The main finding is that there are differences in the brain structure and cognition of persons at risk of developing psychosis compared to the control group. If the parents have experienced psychosis, there may be differences in the child’s brain function,” Miettunen says.

ADHD has also been studied:

“Maternal smoking during pregnancy increases the risk slightly, and the mother’s weight during pregnancy also has an effect. Childhood divorces are also linked with an ADHD risk.”

Professor Jouko Miettunen and Academy Research Fellow Erika Jääskeläinen from the University of Oulu use the cohort material for their psychosis research. In particular, the forecast and risk factors of schizophrenia have been studied extensively. (Photo: Seija Leskelä / Kulmakuvaamo)

Work continues in 2019

According to the researchers, the work has proceeded well despite the enormous number of study subjects in the cohorts from 1966 and 1985 and 1986. Extensive physical examinations were performed on persons born in 1966 when they were 14 years of age. In addition, they have been examined at the ages of 31 and 46. The ones who have experienced psychosis have been examined two times more often.

The persons born in 1985 and 1986 were already examined at the age of 7 or 8, and at the age of 15 or 16. A new examination of this group will be carried out this spring, when the participants are between 33 and 34 years old.

Again this year, the examination will start with a questionnaire, followed by a variety of laboratory tests and measurements. The challenge was to create as comprehensive a questionnaire as possible, taking into account that the participants should be able to fill it in a reasonable time.

The costs of the data collection create another challenge. Examining thousands of people for up to two days costs millions of euros. No funding has been earmarked for this work, but funding has to be applied for in a similar way to all other research. The cohort 1986 data collection is financed, for the most part, by the university itself, as well as by Oulu University Hospital. Different research grants, for example, from the European Union and the Academy of Finland have been received to carry out the research.

Approximately 70% of the cohort members still actively participate in the examinations, and the researchers hope that they will continue to take part in the study as actively in the future.


Text: Raija Tuominen


An all-day event will be organised in Tellus at the University of Oulu on 20 March, presenting the cohort of 1985 and 1986, and the upcoming field study. The event is open to all. More information.



Last updated: 13.3.2019