Table 3.
Sweat micronutrients: Mechanisms and methodological considerations.
| Concentration in sweat | Comparison of regional and whole body sweat | Correlation between sweat and blood | Sweat gland mechanisms | Potential methodological Issues | |
|---|---|---|---|---|---|
| Sodium | 10–90 mmol/L [145–148,156] | Significant correlation; many (forehead, back, chest, upper arm) but not all (foot, calf, thigh) regional sites overestimate whole body concentrations [146,147,149,159] | a [228,295]; plasma [Na] influences sweat [Na], but not reliably correlated because of other factors that dictate reabsorption rates | Secreted via paracellular transport [15]. Primary sweat is nearly isotonic with blood plasma [8,307,434]; Na is reabsorbed in the duct via epithelial Na channels and Na-K-ATPase (activity influenced by aldosterone) [38] transporters [9,34] (see Figure 2), resulting in hypotonic final sweat | Concentration varies (up to 2–3 fold) with sweating rate [6,39,40,159] |
| Chloride | 10–90 mmol/L [147–149,152,159,435] | Significant correlation; many (forehead, back, chest, upper arm) but not all (foot, calf, thigh) regional sites overestimate whole body concentrations [146,147,149,159] | a [152,195]; plasma [Cl] influences sweat [Cl], but not reliably correlated because of other factors that dictate reabsorption rates | Secreted via Na-K-2Cl cotransport model [15]. Primary sweat is slightly hypertonic compared with blood plasma [8,434]; Cl is reabsorbed in the duct via the CFTR [35] (see Figure 2), resulting in hypotonic final sweat | Concentration varies (up to 2-3 fold) with sweating rate [6,152,159] |
| Potassium | 2–8 mmol/L [146,147,435] | Mixed results with respect to correlation [146,147,149,159] | a [228] | Secreted via Na-K-2Cl cotransport model [15]. Primary sweat is nearly isotonic with blood plasma [6,8,434]; Mixed results with respect to relation between flow rate and sweat [K] [6,147,159,436]; thought to be secreted during sweat passage along the duct, but mechanism unknown [437–439] | Often overestimated (by up to 2-3x) with arm bag technique due to surface contamination [134,228] |
| Calcium | b0.2–2.0 mmol/L [144,219,227–229,235,286] | No correlation; regional measures overestimate whole body concentrations [286] | No [283] | NA | Overestimation (by up to 3x) both of epidermal origin and residual Ca in the sweat gland lumen [134,228] |
| Magnesium | b0.02–0.40 mmol/L [219,227–229] | No correlation; regional measures overestimate whole body concentrations [286] | NA | NA | Overestimation (by up to 3x) from skin surface contamination [228] |
| Iron | b0.0001–0.03 mmol/L [219,228,233,234,274] | Regional measures overestimate whole body concentrations [285] | No [233,251] | NA | Overestimation (by up to 2-3x) both of epidermal origin and residual Fe in the sweat gland lumen [134,228,233,234]; cell-rich sweat particularly high in Fe [184,233,234,253,254] |
| Zinc | b0.0001–0.02 mmol/L [219,227–229,274] | Regional measures overestimate whole body concentrations [285] | NA | NA | Overestimation (by up to 2x) from skin surface contamination [228] |
| Copper | b0.0005–0.02 mmol/L [219,227–229,274,285,286] | No correlation; regional measures overestimate whole body concentrations [285,286] | NA | NA | Overestimation (by up to 3.5x) from skin surface contamination [228] |
| Vitamins | a | NA | NA | NA | Overestimation from skin surface contamination and sebum secretions [25,134] |
NA: no data available; amixed results or too few studies available to draw conclusion; bvalues are from regional or whole-body sweat reported from studies that took measures to prevent epidermal contamination (e.g. pre-rinsed skin and analyzed cell-free sweat)