BMI may influence how quickly the body adapts to repeated heat exposure

A controlled exercise-heat study tracked core temperature, heart rate, and sweating in 42 healthy young adults across eight days of repeated heat sessions, comparing those with a BMI below 25 to those above it. Both groups showed some physiological adaptation over time, but the lower-BMI group appeared to adapt more quickly and to a greater degree in terms of core temperature reduction.

What the study found

Both BMI groups eventually showed reductions in peak core temperature by the final session, but the pattern differed. The lower-BMI group showed measurable decreases earlier in the protocol, while the higher-BMI group did not show a statistically significant reduction until the eighth day.

By the end of the eight-day period, peak core temperature was modestly but significantly lower in the lower-BMI group compared to the higher-BMI group. The overall magnitude of core temperature change across the full protocol was also greater in the lower-BMI group.

Heart rate declined and whole-body sweating rate increased across sessions in both groups, and neither of those two measures differed meaningfully between BMI categories. The BMI-related difference appeared specific to core temperature regulation rather than to cardiovascular or sweating responses.

The authors suggest that individuals with a higher BMI may experience a somewhat attenuated or slower core temperature adaptation to repeated heat exposure, though they frame this cautiously given the study's scope and the fact that both groups did ultimately adapt.

Limits worth knowing

The sample was limited to 42 healthy young adults (mean age 23 years), which restricts generalizability to older or less healthy populations. The study used active exercise in a controlled hot environment rather than passive heat exposure, so results may not translate directly to sauna or other sedentary heat modalities. The eight-day window captures early acclimation only; longer-term adaptation trajectories were not examined. Sex-stratified analyses were not reported in detail despite the mixed-sex sample. No funding disclosures were identified in the available information.

About this entry. The Heartwood Review summarizes published, peer-reviewed research in its own words and links to the original source. It is not medical advice; consult a physician before beginning or changing any thermal or recovery practice. Findings summarized here describe the study cited, not any product sold by Teak & Marble Atelier. Corrections.