Heavy metal excretion in sweat: Exercise Superior to Sauna in Controlled Study Original paper

What was studied?

This research study investigated whether the method of sweating—specifically, dynamic exercise versus passive heat exposure—affects the concentration of toxic heavy metal excretion in sweat. The researchers analyzed sweat samples for five specific metals: nickel (Ni), lead (Pb), copper (Cu), arsenic (As), and mercury (Hg). The core objective was to determine if one sweating condition is superior for the purpose of detoxification by comparing the heavy metal excretion in sweat induced by running on a treadmill with that induced by sitting in a sauna cabinet. The study design controlled for environmental factors, with humidity set at 40% for both conditions to prevent differences in sweat evaporation rates. The researchers conducted a pretest using the weighing method to ensure comparable sweat rates between conditions, achieving nearly equivalent rates at 1.8 mg/cm²/min during the 20-minute sweating period and subsequent 30-minute collection extension to ensure sufficient sample volume (>7 mL) for analysis.

Who was studied?

The study recruited 12 healthy young university students from Taiwan, comprising an equal number of men (6) and women (6). The participants were in their early twenties, with mean ages of 21.8 years (SD 0.4) for men and 22.0 years (SD 0.5) for women. Mean height and body mass were 169.2 cm (SD 1.3) and 59.6 kg (SD 7.3) for men, and 160.6 cm (SD 5.1) and 53.2 kg (SD 5.4) for women. All participants were moderately physically active (exercising 3.2 times weekly for men, 1.4 times for women), healthy, asymptomatic of illness, and had no pre-existing injuries. Maximum oxygen uptake was set at approximately fair to good levels (men: 43.0 mL/kg/min, SD 1.6; women: 34.2 mL/kg/min, SD 1.3). To minimize dietary variables that could affect baseline heavy metal excretion in sweat, the participants’ food intake was strictly controlled: all dined in the same restaurant for one year preceding the experiment, and for one week prior to and during the experiment, their food intake was controlled to ensure they all consumed identical meals. Participants were not allowed medication during the study period. The experimental procedures were approved by the Ethics Committee of National Taiwan University (ethical code: 202012EM025), and all participants provided written informed consent.

Most important findings

The study’s primary finding is that the concentration of excreted heavy metals in sweat is significantly influenced by the method used to induce sweating. The concentrations of four out of the five metals analyzed were significantly higher in sweat produced during dynamic exercise (treadmill running) compared to passive heating (sauna cabinet at 45°C).

The experimental protocol was meticulously designed. For the dynamic exercise condition, participants ran on a treadmill (CS-5728, Chanson, Taipei, Taiwan) in a room maintained at 25°C with 40% humidity. The pace was progressively increased from 5 to 10 km/h over the first 10 minutes, followed by an additional 10 minutes of running at the final pace. For the passive heating condition, participants sat inactive in a sauna cabinet set at 45°C with 40% humidity; the cabinet’s controllable range was 40–60°C with 5°C incremental intervals. Sweat was collected from the upper back using a laboratory-made collector (funnel with glass tube, cleaned with deionized water, air-dried, and foil-covered to prevent contamination) over the 20-minute sweating period and a 30-minute extension to achieve the required 7 mL sample. Samples were filtered through 0.22-μm pores to remove cellular debris and skin flakes (>10 μm), acidified with HNO₃, and analyzed within 32 hours. Ni, Pb, and Cu were analyzed using ICP-AES (PerkinElmer Avio 200) with method detection limits of 1.1, 3.0, and 1.5 μg/L respectively; As and Hg were analyzed using ICP-MS (Agilent 7800) with MDLs of 0.03 and 0.05 μg/L respectively. Calibration standards ranged from 0–500 μg/L for Ni, Pb, Cu and 0–5 μg/L for As and Hg. To prevent cumulative fatigue and order effects, tests were separated by two-day intervals and performed in counter-balanced arrangement: participants were randomly divided into groups A and B, with group A running and group B in sauna on day one, then conditions swapped on day two.

The data demonstrate that dynamic exercise leads to significantly greater heavy metal excretion in sweat for Ni, Pb, Cu, and As. The authors provide a physiologically grounded explanation: exercise elevates core body temperature and increases heart rate, shunting warmer, metal-laden blood from the core to the skin where metals are expelled directly via sweat secretion. In contrast, passive heating in a sauna, while raising skin temperature, produces sweat that is more hypotonic with higher water content, diluting metal concentrations. Mercury showed no significant difference, likely because approximately 90% of human body mercury is stored within red blood cells as methylmercury, with only inorganic mercury (about half of which distributes in plasma) available for sweat excretion. The study also observed considerable individual variation in heavy metal excretion in sweat, consistent with expected differences in lifetime exposure and body burden from sources including maternal transfer, diet, and environmental contamination.

The researchers should be commended for their rigorous methodological approach, which addressed numerous potential confounders. The dietary standardization for one year preceding and one week during the experiment is particularly noteworthy, as it minimized a major source of variability in heavy metal body burden. The careful cleaning protocol—scrubbing with tap water and brush followed by deionized water washing—reduced skin surface contamination risks. The matched sweat rates (1.8 mg/cm²/min) between conditions ensured that differences reflected sweat composition rather than sweat volume. The paired t-test design, comparing each participant’s sweat under both conditions, elegantly controlled for individual differences in baseline metal burdens. The use of appropriate MDLs and calibration ranges based on literature values demonstrates thoughtful experimental planning. This study represents a well-designed and rigorously executed investigation that provides novel, valuable information on how different physiological stimuli affect heavy metal excretion in sweat.

While the study provides important and novel findings, it is appropriate to acknowledge its boundaries as invitations for further research. The sauna temperature of 45°C, while selected to match sweat rates with exercise, is lower than many traditional sauna practices where temperatures often reach 70–80°C; future studies employing higher, more clinically representative sauna temperatures might reveal different excretion profiles. The sample size of 12 healthy young Taiwanese adults, while adequate for detecting the large effect sizes observed, would benefit from replication in larger, more diverse populations including older adults, children, individuals with elevated heavy metal body burdens, and different geographic regions with varying environmental exposures. The absence of concurrent blood and urine measurements means we cannot determine what proportion of total body burden these sweat losses represent, nor can we correlate serum levels with sweat excretion rates. The 20-minute sweating duration, while sufficient for sample collection, may not capture steady-state excretion; extended or repeated sweating sessions could yield additional insights. Nevertheless, these limitations do not diminish the study’s significant contribution—they simply highlight the exciting avenues for future investigation that this pioneering work has opened. This study stands as a valuable addition to the literature on human detoxification physiology and provides a strong foundation for subsequent research.

Key implications

For clinicians, this research provides important evidence that the method of sweating significantly influences heavy metal excretion in sweat. If the goal is to facilitate elimination of toxic metals such as lead, arsenic, and nickel, advising patients to engage in dynamic aerobic exercise that induces sustained sweating may be more effective than recommending passive heat exposure alone. The findings suggest that exercise-induced physiological changes—elevated core temperature, increased cardiac output, and enhanced cutaneous blood flow—create conditions favorable for mobilizing and excreting metals sequestered in tissues and circulation. This has particular relevance for populations with known heavy metal exposure risks, including occupational settings, environmental contamination hotspots, and individuals with amalgam dental fillings or specific dietary practices. The study also underscores that sweat composition is not uniform; the stimulus matters. For patients interested in detoxification support, clinicians might consider incorporating moderate-intensity exercise sufficient to produce sustained sweating as part of a comprehensive approach. However, these findings should be integrated with clinical judgment and individual patient circumstances, recognizing that this single study, while rigorous and valuable, represents one piece of an emerging evidence base. The research opens important questions about optimal exercise intensity and duration, the role of repeated sweating sessions, and how these findings might apply to different patient populations—questions that will undoubtedly be addressed as this line of investigation continues.