At 21:44 on October 29, 2003, magnetometers across South America spiked into red. The Halloween solar storms, some of the strongest of Solar Cycle 23, drove Earth’s Kp index to level 9, the maximum for geomagnetic disturbance. In São José dos Campos, a city of 737,000 northeast of São Paulo, dispatchers recorded ambulances rushing two women in their sixties to the municipal hospital with crushing chest pain. Both died before dawn. Their deaths were logged in the Unified Health System database as acute myocardial infarctions, ICD code I21. The timing matched the most severe compression of Earth’s magnetosphere in more than a decade.
Between January 1998 and May 2005, São José dos Campos hospitals registered 1,340 admissions for heart attack. Men accounted for the majority, 871 cases, while women totaled 469. But when researchers overlaid those admissions against the daily planetary Kp index, the global measure of geomagnetic activity compiled in Kyoto, the trend reversed. Women were more likely to suffer during disturbed geomagnetic conditions. On those storm days, women were not just admitted in higher proportions. Their deaths even surpassed men’s.
The team, led by Luiz Felipe Rezende of Brazil’s National Institute for Space Research, worked with anonymized patient data cleared by the Municipal Secretary of Health. Each day in the seven-year period was classified as quiet (Kp sum ≤ 24), moderate (24 < Kp ≤ 32), or disturbed (Kp > 32). Across the study window, there were 2,012 quiet days, 449 moderate, and 213 disturbed. Admissions tracked with those categories: 1,000 on quiet days, 220 on moderate, and 120 on disturbed. What mattered most was not the count, but the ratios.
On quiet days, men were nearly twice as likely to be admitted as women, 665 cases to 335. On disturbed days, the margin shrank sharply, 66 men and 54 women. Fatalities followed the same shift. On quiet days, men recorded 73 deaths, women 58. On disturbed days, women overtook men: 14 to 9. The inversion happened during the very hours Earth’s magnetic field bent under solar wind pressure.
One retired paramedic who worked the October 30, 2003 shift recalled the surge. “It was constant calls, mostly older women, all chest pain,” he said. “We thought it was the heat. But the weather wasn’t extraordinary.” Meteorological records confirm his account: 26°C daytime high, barometric pressure steady, humidity average for spring. No heatwave. The only extreme variable was 150 million kilometers away.
The study period aligned closely with Solar Cycle 23, which peaked between 2000 and 2002. Sunspot counts climbed, coronal mass ejections multiplied, and solar proton events disrupted satellites and aviation. The storms also disrupted infrastructure on the ground. In December 2001, ionospheric irregularities over Brazil’s equatorial belt degraded GPS accuracy for air navigation. During the Halloween storms of 2003, HF radio used by controllers across São Paulo state repeatedly dropped out. Unseen by most, the same disturbances may have been working inside the human body.
The hospital dataset revealed a clear gradient. For women over 60, heart attack frequency rose from 9 percent on quiet days to 13.5 percent on disturbed days. For women between 31 and 60, the rate increased from 7.1 to 11.2 percent. Younger cases were rare but telling. Only one female death under 30 occurred, during a Kp > 32 storm. In men, admissions under 30 were higher, but deaths did not climb during geomagnetic events.
The investigators also used clustering algorithms to probe deeper. Feeding the data into Weka with four attributes—sex, age, Kp sum, and geomagnetic condition—they ran K-Means analysis. One cluster stood apart. Cluster 3 grouped patients with a centroid age of 65.4, centroid Kp sum of 38, predominance female, under disturbed conditions. One hundred and fourteen cases fell here. By contrast, Cluster 4 grouped men with a centroid age of 58.3, predominance male, under quiet conditions, with 226 cases.
The relative frequency analysis confirmed it. On disturbed days, women’s admissions were nearly three times higher than on quiet days. The mechanism is not fully understood, but researchers point to Earth’s resonant frequencies.
Schumann resonances are electromagnetic waves bouncing between Earth’s surface and the ionosphere. Normally they sit at around 7.8 Hz, within the range of human brain activity measured by EEG. During storms, they intensify and shift. That can disrupt melatonin and serotonin regulation, which in turn influences cardiac rhythm, blood pressure, and vascular tone. Animal studies have already shown sensitivity to such low frequencies. The Brazilian results suggest human cardiovascular systems may be vulnerable in similar ways.
The possibility is not new. Soviet scientist Alexander Chizhevsky charted sunspot cycles against epidemics, psychiatric crises, and heart disease in the early 20th century. In 1968, Novikova in Moscow noted a correlation between solar activity and infarction. A decade later, British researchers Knox and Malin published in Nature on the same link. More recently, a 2019 study of 263 US cities tied geomagnetic disturbances to higher cardiovascular mortality. What makes São José dos Campos critical is latitude. Most earlier studies focused on high latitudes near the auroral zones. The Brazilian city sits close to the geomagnetic equator, where disturbances appear differently, yet the health effect was still measurable.
“This is low-latitude evidence,” Rezende noted in study correspondence. “The magnetospheric compression may be global, but its biological consequences are under-examined outside auroral zones.”
Physicians working in the city recall the same pattern. Dr. Ana Carla Mota, a cardiologist at the municipal hospital during those years, said, “It was not diabetes or hypertension alone. There were weeks when older women came in waves, and we could not explain why.”
Autopsy records added another layer. Women in the over-60 group who died during storm days often lacked the expected arterial blockages. Instead, pathologists recorded diffuse ischemia, suggesting electrical rhythm disruption more than mechanical obstruction. That detail supported the idea that geomagnetic shifts may trigger arrhythmias in predisposed patients.
Across the seven-year span, 175 deaths were logged. Of these, 96 were men and 79 were women. Yet on disturbed days, the balance flipped: 14 women, 9 men. That inversion, in a population where men were almost twice as likely to be admitted, points to female susceptibility rather than coincidence.
One surviving patient, Maria de Lourdes, admitted at age 63 during a moderate Kp 6 storm in July 2000, remembered sudden collapse. “I thought it was indigestion. Then everything went black. They told me later it was my heart. I had never had a problem before.” Her case was coded as acute myocardial infarction, but she was discharged alive. Many others were not.
Researchers caution the findings are not final. The dataset covers one municipality. Many personal risk factors—smoking, cholesterol, family history—were not available in the anonymized files. Kp values alone cannot prove causality. Still, the signal was consistent. Women’s admissions and deaths increased on geomagnetically disturbed days.
Solar Cycle 25, already active, is forecast to peak between 2024 and 2026. Disturbed days are increasing. In October 2024, a Kp 8 storm brought auroras as far south as southern Brazil, rare at those latitudes. Hospital administrators in São Paulo have begun tracking admissions informally against space weather alerts.
The next step is scale. A nationwide Brazilian study pulling records from DATASUS across multiple cities would provide the statistical power needed. Replication in Central America, Africa, and Southeast Asia, other low-latitude regions, could confirm whether the effect is universal.
For now, the evidence stands. Between 1998 and 2005, São José dos Campos experienced 213 geomagnetically disturbed days. On those days, women were hospitalized for heart attacks at higher rates and more often died. Public health authorities now face the question of whether to treat space weather as a cardiovascular risk factor.
As of April 2025, the findings have been peer-reviewed and published in Communications Medicine under DOI: 10.1038/s43856-025-00887-7. The authors recommend closer monitoring of at-risk populations when geomagnetic conditions are disturbed. For hospitals, that means watching solar forecasts as closely as weather forecasts.
That is the current status. The next factual step is replication at a national scale before Solar Cycle 25 reaches its peak.
Source:
Rezende, Luiz Felipe C., Eurico R. De Paula, Marcio T. A. H. Muella, Severino L. G. Dutra, Reinaldo R. Rosa, Paulo H. N. Saldiva, and Jean P. H. B. Ometto. “Influence of Geomagnetic Disturbances on Myocardial Infarctions in Women and Men from Brazil.” Communications Medicine 5 (2025): 247. https://doi.org/10.1038/s43856-025-00887-7
