On average, about 700 Americans kill themselves each week — but in the fine-weather weeks of May and June, the toll rises closer to 800, sometimes higher. Every year, suicide peaks with the tulips and lilacs — increasing roughly 15 percent over the annual average to create one of psychiatry's most consistent epidemiological patterns. It may seem perverse that the period of spring and early summer, as the psychologist Kay Redfield Jamison puts it in her splendid book "Night Falls Fast," should contain "a capacity for self-murder that winter less often has." Yet it does.
This grim spring growth confounds conventional belief that suicides peak in winter. It also confounds researchers — and fascinates them. As they discover more angles into the biology of mood and behavior, they are finding new clues about why suicides rise with the sun's arc. They hope solving this puzzle will help us better understand why people commit suicide at all — and perhaps reduce the numbers year-round.
This effort takes an extra urgency from what Dr. Adam Kaplin, a psychiatrist at Johns Hopkins University, calls a "suicide epidemic" — a sharp increase in both absolute and per-capita rates since the recession that began in 2007, particularly among the middle-aged. More than 38,000 people committed suicide in the United States in 2010 — a 16.5 percent jump from the 32,600 suicides five years before, and a new high. The stakes involved in figuring out the dynamics of self-murder seem only to rise with time.
The spring surge in suicides is actually the largest of a few oscillations throughout the year. After dropping to an annual low in February (October in the southern hemisphere), rates climb sharply through spring; fall slowly in summer; show a slight rise, according to some studies, in fall; and then begin a steep winter drop. The spring peak generally runs 10 to 25 percent above the yearly average and 20 to 50 percent above the February low.
The spring increase was first noticed in 19th-century Europe. Many studies, some examining data hundreds of years back, have documented it since. But explaining it has proved difficult, primarily because of suicide's extreme complexity.
"There's no one reason that people do it," said Nadine Kaslow, a research psychologist at Emory University. Rather, she says, people usually commit suicide because personal, social-system and environmental factors combine to push them to a new place of energized despair.
In this view, spring somehow adds weight to an already unbearable load. But how?
One traditional candidate, favored by both Dr. Jamison and Dr. Kaslow, is the "broken promise effect" — the sometimes crushing disappointment that spring fails to bring the relief the sufferer has hoped for.
In addition, psychiatrists have long observed that for patients with bipolar disorder and depression, spring can create a manic agitation that amplifies the risk of suicide — agitation that has long shown itself in a rising rate of hospitalizations for suicide attempts and for manic or schizophrenic episodes in spring and summer.
Researchers have long suspected that this may be tied to the springtime drop in the sleep-friendly hormone melatonin, a reduction that energizes us for spring's longer days but may sometimes help generate dangerous agitation. Yet that link, like many, remains elusive.
In the past decade or so, some researchers have increasingly focused on another candidate: an apparently intimate relationship between suicide and inflammation.
Dr. Kaplin studies depression in patients with multiple sclerosis, an autoimmune inflammatory disease. In M.S., he says, depression and inflammation feed each other: Even after accounting for the psychological effects of any serious illness, M.S. heightens depression risk, and depression amplifies the inflammation central to the disease's central pathologies.
Driving this relationship, Dr. Kaplin suspects, are immune-system chemical messengers called cytokines. Some cytokines increase inflammation, while others curb it.
Inflammatory cytokines play crucial roles in fighting infection, but they can also cause problems. When people with hepatitis C are given the cytokine interferon to help fight the infection, for instance, up to 40 percent become depressed and one in 50 attempt suicide. Other studies suggest that inflammatory cytokine activity reduces levels of the neurotransmitter serotonin and halts the growth of new brain cells — two hallmarks of depression.
If inflammation heightens the risk of depression, how might that lead to a spring surge in suicide?
Dr. Kaplin and others point to several possibilities — "all speculative," he says, not findings to act on but clues to follow. In every case, the suggested risk comes not from a direct effect but from an additional sensitivity to inflammation that could be a final straw or irritant.
A second possibility involves tree pollen. Dr. Teodor T. Postolache, a psychiatrist at the University of Maryland, believes that large amounts of it may cause cytokine-driven inflammatory responses. A study he did links high spring tree pollen counts with high seasonal suicide rates; another examined the brains of 34 suicide victims and found gene-expression patterns consistent with cytokine-driven inflammation.
Yet another possibility involves vitamin D. The low levels caused by lack of sunlight in the winter are thought to lead to inflammation; one recent study tentatively suggested a link to suicide. Dr. Kaplin thus wonders if people already at risk for suicide may increase their risk if they enter spring with inflammatory systems sensitized by vitamin D deficiencies.
"The answer to this puzzle is probably some form of 'all of the above,' " he said.
Even if these inflammatory factors prove out, they will be just some among many — mood disorders, divorce, job loss, grief, trauma — that fertilize spring's darkest bloom. But the more factors researchers can identify, the better we can understand not just the spring surge but the larger mysteries of suicide.
Still, if researchers are ever to identify the seasonal culprits, they may need to hurry. One of the most intriguing findings in the seasonality of suicide is that this ancient pattern appears to be fading — possibly because we all spend more time indoors.
A study of Switzerland's well-kept monthly suicide records between 1880 and 2000, for instance, showed the spring/summer curve growing flatter with each successive 30-year period. Like too many lives lost as we struggle to comprehend suicide, this spring surge may slip away before we can fully glean its unique offerings.David Dobbs is working on a book about the genetic and cultural roots of temperament and behavior.