BY THE OPTIMIST DAILY EDITORIAL TEAM

Forty-eight teams. Sixty-four matches. A final played yesterday at MetLife Stadium in New Jersey. And a victory for Spain, the country taking all the glory home. The 2026 World Cup was the most expansive in the tournament’s history, and for US, Canadian, and Mexican fans, the first played on home soil. The science on what watching all of that does to the human body has been building for decades, and it’s not only fascinating – it’s eye-opening. Here is what it shows.

Watching soccer is not a passive activity. Physiologically, the brain and body respond to a match in ways that parallel actual physical competition, according to Matt Butler, a neuropsychiatry research fellow at King’s College London who recently published research on the behavioral neuroscience of soccer fandom. “While watching our players sweat on the pitch, we respond as if we, too, are playing,” Butler says.

The more invested you are, the stronger the effect. Butler describes a phenomenon called identity fusion, where diehard fans experience what happens to their club almost literally as if it were happening to themselves. With a home World Cup compressing months of national investment into a single tournament, those effects ran high.

Cortisol spikes before the whistle blows

In 2010, researchers measured cortisol in Spanish fans while they watched the World Cup final. Compared to a normal day, fans had significantly elevated levels of the stress hormone throughout the match. The spike was larger in men, in younger fans, and in those most passionate about their team.

The mechanism is what researchers call social self-preservation: humans have a deep need to feel good about themselves and to be seen positively by others. When something threatens that, whether a social rejection or a team loss, the brain treats it as a physical danger and triggers a corresponding stress response.

This stress doesn’t begin at kickoff. When scientists tracked health data from fans of a German soccer club over 12 weeks using smartwatch data, they found cortisol levels began rising as early as 14 hours before a match. Over a 48-team tournament with elimination rounds stretching across a month, that physiological accumulation compounds.

What stress hormones do to the heart

Alongside cortisol, the body’s stress response floods the bloodstream with adrenaline and similar chemicals that speed up heart rate and raise blood pressure, increasing the heart’s demand for oxygen. At the same time, those chemicals constrict the blood vessels feeding the heart, reducing supply. The body needs more oxygen; it gets less. That gap can, in some cases, trigger a heart attack.

Real-world data backs this up. During the 2006 World Cup in Germany, watching a stressful match more than doubled a fan’s chances of a cardiac event that day. During the 1998 World Cup, hospital admissions for heart attacks rose 25 percent on the day England lost to Argentina on penalties and remained elevated for two days, a spike specific to heart attacks, not other conditions. In Spain, a study of domestic league games found a 30 percent rise in cardiac-related hospital visits among men with existing heart conditions on days their team lost.

Butler notes the context: most people start from a low baseline cardiac risk, so a higher relative risk during a match doesn’t mean much in absolute terms. For fans who already have heart conditions, though, it’s a different calculation.

Testosterone rises, and so does sexual activity

Stress hormones aren’t the only thing that changes. During the same 2010 World Cup final, testosterone levels also rose in fans watching the match, and unlike cortisol, this increase was not tied to sex, age, or degree of fandom. “Testosterone is a hormone which is increased in response to competitive situations, so it is perhaps no surprise that levels may be higher when fans watch soccer, regardless of gender,” Butler says.

The urban legend about tournament baby booms also turns out to have some data behind it. During the 2024 UEFA European Championship, researchers tracked the daily sexual behaviors, thoughts, and fantasies of nearly 1,000 participants across five European countries. Fans reported roughly 27 percent more sexual activity in the days following their national team’s wins compared to losses. “Collective rituals and celebrations have been associated with increased intimacy and social bonding since ancient times,” Butler notes.

Sleep loss and its consequences

When a tournament is played far from home, fans stay up late, and the effects go well beyond feeling tired the next morning. During the 2002 World Cup, held in Asia and broadcast in the middle of the night for American viewers, car crash deaths in U.S. towns with large German-American populations rose 35 percent on days Germany played. In towns with the highest concentration of German heritage, the increase reached 122 percent. When researchers later analyzed crash data during a World Cup where games aired at normal hours, the spike was gone, pointing to sleep loss rather than emotional distraction as the cause.

This year’s North American tournament meant most fans in the US, Canada, and Mexico watched at accessible hours, removing that particular risk for home supporters. For fans in Europe and elsewhere who tracked morning kickoffs across six weeks, the calculation looked more familiar.

“Even a single night of sleep deprivation can impair cognitive abilities, particularly concentration,” Butler says.

Soccer may amplify these effects more sharply than other sports. Goals are rare, which makes them disproportionately significant when they happen. Because chance plays a larger role in a low-scoring game, stronger teams can lose and underdogs can win. “This makes it extremely exciting, stressful, and rewarding to watch,” Butler notes. Higher-scoring sports tend to resolve their tension earlier. Soccer keeps you in that state of not-knowing right until the final whistle, and the body stays in it too.

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