Having a high body mass index increases the risk of depressive symptoms over a 5-year period, according to new research.

BMI is a ratio of height and weight that is used to assess whether an individual’s weight is in a healthy range. The new study, published in the Journal of Health Psychology, found that higher BMIs predicted increased future depressive symptoms among older adults.

“Over the last few decades, the percentage of obese older adults in the U.S. has risen considerably. While body mass, an index of weight relative to height often used to define obesity, is just one of many risk factors, there is such an appreciable number of metabolic health sequelae associated with obesity that it is important for us to observe how obesity may also impact psychobiological health as we age,” explained study author Peter Joseph Dearborn of the University of Maine.

“I noticed that while there was a lot of research in recent years regarding body mass and psychological health, much of this research was conducted with younger individuals and rarely did researchers account for the temporal relationships between depressive symptoms and body mass.”

“Essentially, I was interested in the chicken and egg question,” Dearborn told PsyPost. “Does higher body mass predict increases in depressive symptoms, is it the other way around, or does the prediction work in both directions?”

“Testing these bidirectional associations simultaneously allows us to address the ‘file drawer problem’ in research, where negative results are less likely to be published,” Dearborn said. “Is there a true bidirectional association between depressive symptoms and body mass or are null findings just not being selected for publication?”

For their research, Dearborn and his colleagues analyzed data from the Maine-Syracuse Longitudinal Study. The longitudinal study has collected information on more than 2,000 participants over a period of 35 years, including risk factors for cardiovascular disease, clinical cognitive performance measures, and personality and lifestyle measures.

For their new study, the researchers examined 638 participants who were over the age of 50. They found that a higher BMI was linked to a greater risk of depressive symptoms.

“Our results suggest that among older adults, higher BMI was associated with increased levels of depressive symptoms over time, but the reverse was not found,” Dearborn explained to PsyPost.

“Moreover, the effect of BMI on depressive symptoms over time appears to be similar for women and men. That is, while the women in our sample had higher levels of symptoms compared with the men, the increases we observed as a function of BMI were the same regardless of gender.”

The researchers controlled for a number of potentially confounding variables, such as baseline depressive symptoms, age, sex, education, marital status, social isolation, social activity, chronic illness, and physical functioning.

But the study still has some limitations.

“There are a few caveats to this or any study which is why human research is so interesting!” Dearborn remarked. “It allows us to keep asking questions to get a better picture of the complex human condition.”

“First off, humans are not monolithic. At the level of the individual, a higher BMI does not mean that an increase in symptoms will definitely be experienced. These results are pooled over hundreds of individuals with varying levels of risk.”

“Second, even though we did our best to account for risk factors associated with BMI and symptoms, this was an observational study, so causality eludes us,” Dearborn continued.

“Third, our models accounted for under half of the observed changes of depressive symptoms over the five year period, which leaves plenty of room for other explanatory variables. For example, experiencing weight stigma has been associated with depressive symptom risk and has increased in prevalence over the last couple decades despite higher BMIs being more common than ever.”

“Lastly, our sample had a lack of underweight individuals and there is research to suggest that both underweight and obese individuals may have higher symptom risk compared with adults in the middle of the spectrum.”

“I think it is important to note that even minor changes in daily behavior over time can be effective in preventing depressive symptom risk,” Dearborn added. “Several studies have shown that increasing one’s level of physical activity (e.g., walking, gardening, bike commuting, etc.) can lower symptom risk independent from any potential changes in one’s weight status.”

The study, “Challenging the ‘jolly fat’ hypothesis among older adults: High body mass index predicts increases in depressive symptoms over a 5-year period“, Michael A Robbins and Merrill F Elias.