Her death followed heart surgery to correct a congenitally weak valve, said her husband, Richard Nolen-Hoeksema.

Dr. Nolen-Hoeksema, a professor at Yale University, began studying depression in the 1980s, a time of great excitement in psychiatry and psychology. New drugs like Prozac were entering the market; novel talking therapies were proving effective, too, particularly cognitive behavior therapy, in which people learn to defuse upsetting thoughts by questioning their basis.

Her studies, first in children and later in adults, exposed one of the most deceptively upsetting of these patterns: rumination, the natural instinct to dwell on the sources of problems rather than their possible solutions. Women were more prone to ruminate than men, the studies found, and in a landmark 1987 paper she argued that this difference accounted for the two-to-one ratio of depressed women to depressed men.

She later linked rumination to a variety of mood and behavior problems, including anxiety, eating disorders and substance abuse.

“The way I think she’d put it is that, when bad things happen, women brood — they’re cerebral, which can feed into the depression,” said Martin Seligman, a professor of psychology at the University of Pennsylvania, who oversaw her doctoral work. “Men are more inclined to act, to do something, plan, beat someone up, play basketball.”

Dr. Seligman added, “She was the leading figure in sex differences in depression of her generation.”

Dr. Nolen-Hoeksema wrote several books about her research for general readers, including “Women Who Think Too Much: How to Break Free of Overthinking and Reclaim Your Life.” These books described why rumination could be so corrosive — it is deeply distracting; it tends to highlight negative memories — and how such thoughts could be alleviated.

Susan Kay Nolen was born on May 22, 1959, in Springfield, Ill., to John and Catherine Nolen. Her father ran a construction business, where her mother was the office manager; Susan was the eldest of three children.

She entered Illinois State University before transferring to Yale. She graduated summa cum laude in 1982 with a degree in psychology.

After earning a Ph.D. in psychology at the University of Pennsylvania, she joined the faculty at Stanford. She later moved to the University of Michigan, before returning to Yale in 2004.

Along the way she published scores of studies and a popular textbook. In 2003 she became the editor of the Annual Review of Clinical Psychology, an influential journal.

Dr. Nolen-Hoeksema moved smoothly between academic work and articles and books for the general reader.

“I think part of what allowed her to move so easily between those two worlds was that she was an extremely clear thinker, and an extremely clear writer,” said Marcia K. Johnson, a psychology professor and colleague at Yale.

Dr. Nolen-Hoeksema lived in Bethany, Conn. In addition to her husband, a science writer, she is survived by a son, Michael; her brothers, Jeff and Steve; and her father, John.

“Over the past four decades women have experienced unprecedented growth in independence and opportunities,” Dr. Nolen-Hoeksema wrote in 2003, adding, “We have many reasons to be happy and confident.”

“Yet when there is any pause in our daily activities,” she continued, “many of us are flooded with worries, thoughts and emotions that swirl out of control, sucking our emotions and energy down, down, down. We are suffering from an epidemic of overthinking.”