Losing childhood weight by adulthood might erase later depression risks

A person’s body size during childhood and adulthood is linked to their risk of developing depression and anxiety later in life, but achieving a normal adult weight might help mitigate early risks. In a massive new study, researchers found that while being heavier or thinner than average as a child relates to higher mental health risks, reaching a normal weight by adulthood seems to erase that excess vulnerability. The research was published in the Journal of Affective Disorders.

Mental health disorders and obesity are two of the most prominent health challenges globally. Millions of people live with depression or anxiety, and global obesity rates continue to rise among both children and adults. Past research routinely connects adult obesity to higher rates of psychological distress.

The relationship between body weight and mental health involves both biological and social components. Adipose tissue, or body fat, can release inflammatory molecules that cross into the brain and influence neurotransmitter activity. Elevated body weight can also alter the body system responsible for managing stress responses. People living with obesity often face social stigma, body dissatisfaction, and discrimination, which can negatively affect their overall well-being.

While the association between adult weight and mental health is well documented, the influence of childhood body size remains less understood. Many previous studies have treated childhood weight and adult weight as entirely separate events. This approach misses the dynamic nature of human development and the ways weight can fluctuate over a lifetime.

To explore this, a team of researchers investigated how the trajectory of a person’s body size from childhood to adulthood relates to their mental health. The research team was led by Dong-Run Li, Ke-Ru Li and Bang-Quan Liu, along with corresponding author Qi-Jun Wu, all based at China Medical University. They wanted to see if the mental health risks associated with childhood weight were permanent or if they could be altered by weight changes later in life.

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The researchers analyzed data from a massive sample of 368,756 participants in the UK Biobank, a long-term health registry tracking residents across the United Kingdom. All participants were adults between the ages of 40 and 69 at the time they joined the study. The researchers excluded anyone who already had a diagnosis of depression or anxiety at the beginning of the tracking period to focus strictly on new cases.

At recruitment, participants reported what their body size was like at age 10 compared to their peers, choosing between thinner, average, or plumper. The researchers also measured each participant’s current Body Mass Index. Body Mass Index is a standard metric that divides a person’s weight by the square of their height to categorize them as normal weight, overweight, or obese.

The team followed the participants for a median of just over 13 years. During that time, they tracked medical records and self-reported health questionnaires to identify new diagnoses of mental health conditions. By the end of the tracking period, the researchers recorded 11,546 new cases of depression and 15,780 new cases of anxiety.

When looking at childhood body size alone, the researchers found that any deviation from the average at age 10 was associated with an elevated risk of later mental health issues. Participants who remembered being thinner than average had a 9 percent higher risk of depression and a 13 percent higher risk of anxiety. Those who recalled being plumper than average faced a 19 percent increased risk of depression and an 11 percent increased risk of anxiety.

Adulthood weight showed an even stronger association with mental health outcomes. The relationship appeared as a U-shaped curve, meaning that risks were lowest in the middle and higher at both extremes. The lowest risk for depression occurred at a Body Mass Index of about 23 to 24, which falls securely within the normal weight category.

As adult weight increased beyond the normal range, the risk of developing depression and anxiety rose steadily. Participants classified as overweight had an 18 percent higher risk of depression compared to those of normal weight. For participants with obesity, the risk of depression was 52 percent higher, and the risk of anxiety was 15 percent higher.

The most revealing results came from combining childhood and adulthood body sizes to look at lifetime trajectories. The researchers divided the participants into nine different groups based on how their weight changed, or stayed the same, from age 10 to adulthood. Adulthood weight status proved to be the dominant factor in predicting future mental health.

Participants who went from being thinner as a child to obese as an adult exhibited the highest risks overall. That specific group faced a 73 percent higher risk of depression and a 33 percent higher risk of anxiety compared to people who maintained an average and normal weight throughout their lives. Participants who were average in childhood and became obese in adulthood also showed elevated risks.

To understand the direct impact of adult weight, the research team conducted a statistical mediation analysis. They found that adult Body Mass Index accounted for about 45 percent of the association between childhood plumpness and adult depression. Adult weight also explained about 31 percent of the link between childhood plumpness and adult anxiety. This suggests that the link between childhood plumpness and adult mental health may be partially explained by elevated body weight persisting or worsening into adulthood.

However, childhood adiposity did not guarantee a higher risk of mental health conditions in adulthood. Participants who reported being plumper in childhood but measured at a normal weight in adulthood showed no statistically significant increase in their risk for depression or anxiety. Their mental health risks were comparable to individuals who had been an average size as children and maintained a normal weight as adults.

This finding suggests that the psychological risks associated with being a heavier child are potentially reversible. Achieving and maintaining a normal body weight in adulthood seems to mitigate the early vulnerabilities linked to childhood weight. Interventions focused on optimizing adult weight could yield broad psychological benefits regardless of a person’s starting point in childhood.

The study relied on participants recalling their body size from age 10, which occurred decades prior to the data collection. Memories can be imperfect, and this extended gap introduces the possibility of recall bias. The comparative categories of thinner, average, and plumper are also subjective, though researchers note that people tend to retain a general sense of their relative size compared to peers.

As an observational study, the research cannot prove that body size directly causes depression or anxiety. Other unmeasured biological, environmental, or social factors might influence both a person’s weight and their mental health simultaneously. Future research could incorporate genetic data or repeated real-time weight measurements throughout a person’s life to better understand the biological mechanisms at play.

The UK Biobank mostly consists of volunteers of European descent, which can limit how these findings apply to different global populations. Volunteer-based health studies also frequently attract individuals who are generally healthier than the broader public. The researchers combined different medical codes to track depression and anxiety without separating specific subtypes of these disorders, which might relate to body weight in different ways.

The study, “Life-course trajectories of body size from childhood to adulthood and risk of incident depression and anxiety: a prospective cohort study,” was authored by Dong-Run Li, Ke-Ru Li, Bang-Quan Liu, Jia-Cheng Liu, Wen-Rui Zheng, Ting-Ting Gong, Shan-Yan Gao, and Qi-Jun Wu.