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SAN FRANCISCO — Higher caffeine intake was associated with more severe depressive symptoms overall but also appeared to lessen the relationship between depression and severe insomnia and stress, new research showed.

In a cross-sectional analysis of more than 1000 adults participating in the Sleep and Healthy Activity, Diet, Environment and Socialization (SHADES) study, investigators found that higher caffeine intake, insomnia, sleepiness, fatigue, and stress were each independently associated with higher scores on the Patient Health Questionnaire-9 (PHQ-9) depression scale.

The association between severe insomnia and depression was strongest among those who did not consume caffeine. While moderate-to-severe insomnia remained linked to higher depression scores regardless of caffeine intake, the relationship appeared weaker among caffeine consumers. Similar findings were observed for poor sleep quality. 

Study investigator Mira Kaur Marwah, a medical student at the University of Arizona College of Medicine-Tucson, said the findings suggest caffeine use may influence the relationship between sleep disturbances and depression. 

The findings were presented May 17 at the American Psychiatric Association (APA) 2026 Annual Meeting. 

Connections ‘Not Well Studied’

Although depression, sleep disturbances, stress, and fatigue are often interconnected, their relationship with caffeine consumption “has not been well studied,” Marwah told Medscape Medical News.

Marwah said she was motivated to conduct the research because she was interested in how people potentially use caffeine to cope with depressive symptoms, such as low energy and poor alertness, and whether caffeine consumption might mask some manifestations of depression. 

“My goal was to look at, on a more biopsychosocial level, how caffeine affects all of these things,” she said. 

The researchers assessed data for 1007 adults aged 22 to 60 years with a generally even split between men and women. 

Outcome measures included the PHQ-9 depression scale, the Fatigue Severity Scale, the Perceived Stress Scale, the Insomnia Severity Index, and the Epworth Sleepiness Scale.

Caffeine intake through coffee or energy drinks was assessed by the number of servings consumed per day. Caffeine intake through soda consumption was not evaluated. 

Results showed that three to four servings (P = .03), five to six servings (P = .004), and seven or more servings (P = .01) per day of caffeine were independently associated with higher PHQ-9 scores.

Mild and moderate-severe insomnia and high levels of sleepiness, fatigue, and stress (all, P < .0001) were also each associated with high depression scores. 

Caffeine consumption, however, appeared to modify the relationship between insomnia and depression. Among participants with moderate-to-severe insomnia, the strongest association with higher PHQ-9 scores was observed in nonusers of caffeine (B, 13.5; P < .001). Although still significant, the relationship was weaker among those consuming one to seven or more daily servings of caffeine (Bs, 8.0-9.2; P < .001 for all).

The findings were similar for those with poor sleep quality. Non-caffeine consumers again showed the greatest association with higher depression scores (B, 11.8; P < .001), with the association still high but attenuated for those who drank one to two and three to four servings (B, 8.7; P < .001 for both), five to six servings (B, 9.35; P = .004), and seven or more (B, 6.7; P = .01) servings per day.

A Complex Issue

Gregory Scott Brown, MD, chair of the APA's Council on Communications, applauded the researchers for looking into the relationship between caffeine, depression, and other conditions but cautioned that all of this represents a “complex issue.”

“I think this is just the tip of the iceberg and there’s a lot more research that needs to be done,” he told Medscape Medical News. Brown, who was not involved with the research, is also clinical associate professor at the University of Houston College of Medicine, Texas.

Brown noted several study limitations, including the lack of a standardized definition for caffeine serving size, no distinction between black coffee and coffee consumed with sugar, and the possibility that habitual and new caffeine users may differ.

“It’s a really interesting study and I’m glad the researchers did it. But it opens this entire Pandora’s box of questions that we need to look into,” he said.

Caffeine is a psychoactive substance, and clinicians should routinely ask patients about their caffeine intake, Brown said, noting that such discussions are often overlooked in clinical practice.

“However, caffeine has different effects on different people and it’s important that we’re not generalizing based on a study that only looks at the surface of a very complex topic,” Brown said. 

Marwah and Brown reported no relevant financial relationships.