Behavioral risk factors including smoking, obesity, limited physical activity and a less healthy diet strongly predict the likelihood of depression — and that likelihood increases with each additional risk factor a person possesses. Additionally, the risk factors most strongly linked to depression change with age.


Previous studies had identified behavioral risk factors for depression, but it was unclear how these variables changed across the lifespan. This study sought to identify how the risk factors varied among three age groups: younger (18-39 years old), middle-aged (40-59) and older (60-99) adults.


The researchers collected data from more than 30,000 survey respondents, who answered questions about their lifestyle, including smoking, weight, physical activity and diet, as well as their history of depression. The team looked for correlations between the risk factors and depression, controlling for variables such as gender, ethnicity and socioeconomic status.

Sixteen percent of all participants had a prior diagnosis of depression. Smoking was most strongly associated with depression, especially in younger people: Younger smokers had 2.7 times’ greater odds of having had depression, while middle-aged and older smokers had 1.8 times the odds, compared to nonsmokers of the corresponding age. Obesity was the next most important risk factor: younger, middle-aged and older obese respondents had 65 percent, 54 percent, and 67 percent greater likelihood of depression, respectively, compared to non-obese counterparts.

Participants who had little physical activity were more likely to have depression as they grew older. And a less healthy diet was linked to depression in the middle-aged and older groups only.

Importantly, compared to having no risk factors, having one risk factor increased the odds of having had depression (1.7 times). When a person had two risk factors, the odds of developing depression more than doubled. Having three risk factors increased the odds of developing depression by more than threefold, and a person with all four risk factors had almost six times the likelihood of depression.


The study is the largest yet to examine the behavioral risk factors for depression across age groups. Given the psychological, social and economic toll of depression, as well as its growing prevalence, predicting a person’s risk at any age is critical, as are age-specific prevention programs, according to the authors. They said further research about nuanced risk factors, including gender and ethnicity, are warranted.


Natacha Emerson, a postdoctoral fellow in the department of psychiatry and biobehavioral sciences,

Jane and Terry Semel Institute for Neuroscience and Human Behavior at UCLA, David Geffen School of Medicine at UCLA, is the study’s first author. Prabha Siddarth, a biostatistician in the same department, is the study’s senior author. Other UCLA-affiliated authors are Gary Small, David Merrill, Stephen Chen and Fernando Torres-Gil.


The study was published in the journal Mental Health & Prevention.


The work was funded by the Gallup Organization, the Parlow-Solomon Professorship on Aging, and the UCLA Longevity Center.


UCLA owns a U.S. patent titled “Methods for Labeling βAmyloid Plaques and Neurofibrillary Tangles.” Small is among the inventors, has received royalties, and may receive royalties on future sales. Small owns equity interest in Ceremark Pharma LLC, which has licensed the technology from UCLA. Small reports having served as a consultant and/or having received lecture fees from AARP, Allergan, Axovant, Forum, Herbalife, Lundbeck, Lilly, Novartis, Otsuka and Roche.