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Aging induces many changes in body composition, even in the absence of changes in body weight. Typically, as a person ages, their fat mass increases, and the muscle mass and bone mineral density decrease. Findings from a recent study suggest that sauna use increases muscle and bone mass.

Sauna use involves transient exposure to heat, stressing the body and eliciting a wide range of protective responses. Evidence indicates that heat stress may promote muscle growth via activation of pathways involved in protein synthesis and drive osteogenesis via activation of heat shock proteins.

The intervention study involved 23 healthy young males (average age, 20 years). Participants completed questionnaires regarding their physical activity and nutritional intake. Half of the participants engaged in 12 sauna sessions, performed three times per week for four weeks. Each session consisted of five sets of 10-minute exposures at 100°C (212°F), with five minutes of recovery at 22°C (room temperature, ~72°F) between sets. The other half carried out normal activities for the duration of the study. The participants underwent bioelectrical impedance and dual-energy X-ray absorptiometry (DEXA) to gauge body composition prior to the first sauna session, at the completion of the last sauna session, and two weeks later.

None of the participants experienced any changes in fat mass during the study. However, the DEXA scans revealed that the men who engaged in the sauna sessions experienced increases in their muscle mass, bone mineral content, and bone mineral density, compared to the men who did not engage in sauna sessions.

These findings suggest that heat stress encountered during sauna use exerts favorable changes in lean body composition. Learn more about the health benefits of sauna use in this review by Dr. Rhonda Patrick.

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