A new study shows that obesity in childhood is associated with a higher overall disease burden later in life. As adults, these individuals are diagnosed more often in hospital settings but largely within the same overall disease patterns as the rest of the population.
Childhood overweight leads to more hospital diagnoses later in life. Children with obesity have, on average, a greater disease burden later in life than children who had normal weight, according to a new registry study conducted at the Center for Clinical Research and Prevention at Bispebjerg and Frederiksberg Hospital in Denmark.
The scientific article has just been published in the journal Obesity and suggests that obesity in childhood, in particular, is linked to a higher number of hospital diagnoses later in life. The study therefore points to differences in the overall disease burden rather than to the emergence of new disease patterns – that is, how often people need hospital-based care across their lives.
The study was carried out by a research group at the Center for Clinical Research and Prevention, led by PhD and Research Associate Julie Aarestrup, who investigated how childhood body mass index (BMI) is related to the overall burden of diseases throughout adulthood.
“We can use childhood BMI as an early indicator of the overall disease burden later in life,” says Julie Aarestrup. “Instead of looking at a single diagnosis at a time, we look at the entire disease pattern across adulthood – both how many hospital contacts people have and what types of diseases they encounter in the healthcare system over time.”
“This provides a clear picture of differences in disease burden over time,” she continues. “People who had obesity in childhood have more hospital diagnoses in adulthood than those with normal weight as children, and the most striking finding is that overweight and obesity also appear as hospital diagnoses later in life.”
Disease development seen in context
The link between overweight in childhood and disease later in life has been examined before, Julie Aarestrup points out. Previous studies have typically focused on one diagnosis at a time, such as type 2 diabetes, cardiovascular disease or certain types of cancer. They have provided important pieces of the puzzle in understanding how body size early in life can signal later disease but say less about how an entire disease trajectory unfolds over time.
In reality, most people encounter the healthcare system many times throughout their lives with different problems that, taken together, form a broader picture. Julie Aarestrup and her colleagues are trying to capture this picture by looking at patterns across diagnoses rather than singling out individual diseases.
The research group draws on data from the Copenhagen School Health Records Register, which contains mandatory school health examinations of children born in Copenhagen throughout much of the twentieth century. From this register, 112,952 children born between 1962 and 1996 were included in the study, all with recorded measurements of height and weight at the age of seven.
Based on these measurements, the researchers calculated BMI and divided the children into four weight groups: underweight, normal weight, overweight and obesity, in accordance with international guidelines for children’s BMI. Around 4% had underweight, just over 83% fell within the normal range, a little over 9% had overweight, and around 3–4% had obesity in childhood.
From school records to lifelong disease development
Drawing on school health records and later hospital contacts, the researchers followed the children from the first measurements taken at school age through to around the age of 60 years, examining how both the number of diagnoses and overall disease patterns relate to BMI in childhood.
The transition from school records to adult life is made possible by the Danish personal identification number, which enables each individual to be linked to national registers of hospital contacts and disease diagnoses. The researchers used data from the National Patient Register and the Psychiatric Central Register and followed participants from age 15 until age 60 or until they left the registers because of death, emigration or the end of follow-up.
For each person, all hospital-based diagnoses were included, covering both admissions and outpatient treatment. The diagnoses were grouped using three-digit international diagnostic codes, which bring related conditions together into broader disease categories. This means the analysis captures the overall clinical disease burden over time – rather than minor differences in registration practice.
“We did not select specific diagnoses in advance or limit ourselves to particular disease areas,” explains Julie Aarestrup. “Instead, we analysed the 50 most common diagnoses in each combination of sex and childhood BMI group and followed their development from adolescence to retirement age.”
The diagnoses were analysed using statistical methods that make it possible to estimate how many different diagnoses an average person in each group has accumulated in adulthood. In this way, the material provides both a measure of the overall burden of diseases and a picture of the types of conditions that most commonly occur over time.
Childhood obesity is linked to longer medical records
When the researchers looked at the number of diagnoses, a clear pattern emerged. By the age of 60 years, people with obesity as children have, on average, had more hospital diagnoses recorded than those who were, for example, within the normal weight range at the age of seven years.
Among women with obesity in childhood, the average number of diagnoses at age 60 is 18.2, compared with 14.7 among women with normal weight as children. For men, the corresponding figures are 15.1 diagnoses versus 11.7. The numbers include both acute episodes and long-term illness and, taken together, point to more frequent contact with the hospital system throughout adulthood when childhood weight has been at the higher end of the scale.
A further question is whether the disease pattern itself also changes when comparing, for instance, normal weight and obesity in childhood. Here, the analysis shows that the 50 most common diagnoses are broadly distributed across the same disease categories across childhood BMI groups, for both men and women.
In other words, people with obesity as children go through adult life with many of the same types of diseases as the rest of the population – but they experience them more often. On the basis of these data, the researchers cannot determine whether the difference reflects biological consequences of early overweight, social conditions, differences in health behaviour or an interaction between several mechanisms.
Association, not explanation
One diagnostic area nevertheless stands out clearly. Among both women and men with obesity as children, the most frequent hospital-based contact in adulthood is a registration of overweight or obesity. Among women in this group, just over a third have received such a diagnosis before the age of 60 years, while the same applies to just over one in 10 men.
The diagnosis of overweight or obesity is underrepresented in the registers, since many cases are managed in general practice or are not recorded as a separate diagnosis in the hospital system at all. Even so, it is far more prominent among adults with obesity in childhood.
Julie Aarestrup emphasises that the high occurrence of overweight and obesity as a hospital diagnosis among those with obesity as children does not stand alone but is accompanied by a generally greater accumulation of both somatic and other diagnoses across the life course.
Hospital data provide strengths and blind spots
The analysis is based on registers that include only diseases diagnosed within the hospital system. This is a clear strength, because everything that is recorded is included systematically and because all participants are followed over many years.
At the same time, it means that illnesses often managed by, for example, a general practitioner are less visible in the material. This applies to common chronic conditions that are primarily treated in the primary care sector and to some weight-related care.
This is precisely why it is important to be cautious when interpreting the diagnosis of overweight or obesity, Julie Aarestrup emphasises. “The diagnosis is recorded when you have contact with the hospital system and when the doctor chooses to register the code,” she says. “Many people with overweight or obesity will never be recorded with a diagnosis.” The fact that this diagnosis nonetheless emerges as the most common among adults with obesity as children therefore makes the finding all the more striking.
Another limitation concerns who was included in the study. All the children come from schools in Copenhagen, meaning that the analysis is not a nationwide portrait of Danish children. The research group nevertheless has no strong reason to expect markedly different patterns elsewhere in the country.
Conversely, it is precisely the combination of school health records and national registers that makes it possible to follow disease patterns from childhood into adulthood with such a high level of detail.
Next step: diseases that occur together
The current analysis is descriptive and should primarily be read as a map of how hospital diagnoses are distributed across the life course based on different BMI groups in childhood. The map says something about differences in burden but cannot in itself explain why these differences arise. Even so, the results point to several clear next steps.
“We are very interested in how diseases occur simultaneously in the same person,” says Julie Aarestrup. She emphasises that the next natural step in the research is to examine multimorbidity – that is, the combinations of diagnoses that occur at the same time.
The research group will therefore continue to explore whether certain patterns of concurrent diagnoses are more common when overweight or obesity has been present since childhood. The question is whether the significance of weight is mainly about a greater number of contacts spread over the years or whether it also shapes more complex courses in which several diseases develop in parallel.
Answers to these questions could provide a stronger basis for both prevention and capacity planning in the healthcare system – a system in which early differences in health can propagate over decades.
