Joint Analysis of Heatstroke by Nissay Plus and MDV: Clarifying the Reality Through Insurance and Medical Big Data

Nissay Plus Small-Amount Short-Term Insurance Co., Ltd. (President: Hideyuki Imanishi), a group company of Nippon Life Insurance Company (President: Satoshi Asahi), and Medical Data Vision Co., Ltd. (MDV) (President: Masaki Nakamura), have compiled data on heatstroke based on insurance data held by Nissay Plus and the largest-scale medical database in Japan held by MDV.

The analysis revealed that interest in heatstroke, as indicated by insurance enrollment, varies by region across Japan. Furthermore, while the male-to-female ratio of hospitalized patients is 6:4, women tend to have longer hospital stays. Heatstroke is a condition where the body's thermoregulation fails in high-temperature, high-humidity environments, leading to heat retention. Symptoms include dizziness, headaches, and nausea, and severe cases can be life-threatening.

1. Hospitalized heatstroke patients: 6:4 male-to-female ratio According to MDV's medical database (61.21 million actual patients, as of April 2026), an examination of heatstroke patients hospitalized at 432 hospitals between April 2022 and March 2025 (36 months) showed 11,895 patients. Over 30% were aged 80–89, followed by over 20% aged 70–79. While the male-to-female ratio was 6:4, women showed a tendency for longer hospitalization. It was also found that many patients were hospitalized long-term in November.

Regarding comorbidities, COVID-19 followed "dehydration" as a top diagnosis. However, most COVID-19 cases were identified as "suspected diagnoses," suggesting the difficulty of triage during emergency transport.

[Doctor's Comment: Dr. Masafumi Ito, Chairman and Hospital Director, Tojun Hospital, Shakai Iryo Hojin Jiseikai] "Emergency admissions for heatstroke begin around June. We often see elderly patients from households with elderly care or single-living situations whose condition worsens, and their hospital stays are prolonged by complications such as aspiration pneumonia or urinary tract infections. As people age, they become less sensitive to heat and may stop adjusting indoor temperatures, leading to heatstroke. Admissions from elderly care facilities are also increasing; we must be vigilant not to overlook the early stages. Since hot days continue beyond summer, caution is essential. I advise the elderly to drink water at set times, thinking of it as 'medicine,' rather than waiting until they are thirsty."

While enrollment in Nissay Plus's heatstroke insurance generally correlates with ambulance transport data from the Fire and Disaster Management Agency, a significant gap remains: while over 50% of hospitalized heatstroke patients are 70 or older, only 7% of insurance policyholders are in this age group.

2. Regional characteristics of insurance enrollment Analysis of enrollment rates by region showed that the coefficient for the western Japan area was higher. This suggests that regional climate and differences in awareness of preparedness for heatstroke are key factors.