Long term effects of peak strenuous effort on serum magnesium, lipids, and blood sugar in apparently healthy young men.

Earlier findings showed a sustained lowering of serum magnesium concentration (S-Mg) which indicated the presence of Mg deficit, and a parallel, delayed rise of blood sugar and serum lipids as a sequel to strenuous effort. S-Mg was still significantly decreased 3 months after termination of peak effort. To gain further perspective, we followed the biochemical sequels of exertion over an extended period of observation, while maintaining the same experimental conditions used earlier, which mimicked those employed in the training of military recruits. We examined two groups of military recruits, n = 15 (group 1), n = 16 (group 2), mean age 18.6, SD 1.3 and 18.7, SD 0.6, years respectively, who underwent a graded training programme of 7 months' duration culminating in a 120 km forced march. Blood was sampled for estimation of S-Mg in 20 soldiers on recruitment, 6 and 10 months after the 120 km march in group 1, and 9, 11 and 15 months after the march in group 2. Blood sugar and serum lipids were screened on recruitment and up to 11 months after the 120 km march. A significant lowering of mean S-Mg was found as late as 10 months after completion of the march in group 1, and 11 months in group 2 (P less than 0.01). Mean serum cholesterol and triglycerides showed a delayed rise, especially in group 2 (P less than 0.05 and P less than 0.001, respectively), whereas blood sugar decreased in group 1, but increased in group 2 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed metabolic changes after strenuous exertion in trained young men.

Twenty apparently healthy, young male volunteers, aged 18-25 (mean 19.3, SD 1.4) years received a 6 months standardized, graded outdoor physical training and were screened for serum magnesium concentration (S-Mg), serum calcium concentration (S-Ca), serum aspartate amino transferase (S-AST), serum alanine amino transferase (S-ALT), serum creatine kinase activity (S-CK), other laboratory variables, weight, and VO2 ml.kg-1.min-1 [corrected] (VO2 max), before a 70 km march, as well as at 1, 24 and 72 h and 18 days after. Maximal aerobic power, body weight, haemoglobin, haematocrit, serum creatinine, total protein and albumin remained unchanged throughout. Immediately after the march, S-Mg did not change, S-AST, S-ALT and S-CK rose, but the rise was not statistically significant, while small but significant rises in S-Ca (P less than 0.05, Student's t-test) and serum cholesterol (P less than 0.01) normalized at 24 h. At 72 h after the march, a significant fall in S-Mg was found (P less than 0.01), together with a second significant rise in S-Ca (P less than 0.05). After 18 days, with no intervening marches or dietary changes, S-Mg remained significantly lowered (P less than 0.05), mean S-ALT and S-CK became significantly raised for the first time (P less than 0.001 and P less than 0.01 respectively), whereas S-Ca normalized. Concomitantly, for the first time there was now a significant rise in blood sugar (P less than 0.001), serum triglycerides (P less than 0.01), and a second rise of serum cholesterol (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in serum magnesium concentration after strenuous exercise.

Serum magnesium concentration (S-Mg) was measured in 20 highly trained young men (mean age 19.5, +/- 0.5, range 18-20.5) before, and at 1 hour, 24 hours, 72 hours, and 3 months after a 120 km hike. As found in previous studies, S-Mg was significantly decreased at the end of the hike (p less than 0.001, [corrected] Student's t-test). In this group S-Mg had risen significantly after 24 hours in relation to the value at 1 hour (but not to starting value); yet, at 72 hours and 3 months later, it was once more significantly lower than the starting value (p less than 0.001 and p less than 0.05, respectively, Student's t-test). A marked elevation in serum creatine kinase activity (CK) suggests that the rise in S-Mg observed at 24 hours is the result of either exertional rhabdomyolysis or loss of membrane integrity, as a result of the strenuous exertion, since the CK had fallen sharply by 72 hours after the hike. The biphasic, statistically significant, lowering of S-Mg which persisted after 3 months suggests that strenuous exertion induces magnesium deficiency.

Measurement of magnesium in human tissues and fluids: a historical perspective.

The history of the development of methods to measure magnesium in biological systems is reviewed. The current optimal methods are discussed in detail as are some highly sensitive methods which may be used in special circumstances.

Revisiting the Holy Cross football team hepatitis outbreak (1969) by serological analysis.

Clinical and biochemical data collected during the Holy Cross College football team hepatitis A outbreak in 1969 suggested that 32 team members had icteric hepatitis, 58 had anicteric illness, and only seven were not infected. Using a currently available radioimmunoassay, we tested stored serum samples obtained during the outbreak for IgM antibody to hepatitis A virus (IgM anti-HAV). Only individuals with icteric hepatitis were found to have IgM anti-HAV in serum; those with presumed anicteric illness were shown not to be infected with hepatitis A virus. The attack rate was thus only 34%, not 93% as originally reported, and the incidence of icteric illness in those infected was 100%, not 33%. This serological analysis of a classic outbreak of hepatitis A illustrates the utility and importance of IgM anti-HAV testing in seroepidemiologic investigations of hepatitis outbreaks.

Comparison of diluents for serum magnesium estimation by atomic absorption spectrophotometry.

In order to determine the optimal diluent for the determination of Mg by atomic absorption spectrophotometry, the following diluents were tested: deionized water, 0.1 mol/l HCl, 2.5 g/l SrCl2, 1.8 g/l LaCl3, 17.7 g/l LaCl3, half-saturated 8-hydroxyquinoline (oxine), 40 g/l trichloroacetic acid (TCA)/17.7 g/l LaCl3, and 100 g/l TCA/0.1 mol/l HCl. The calibration curves, obtained on the same day, were passed through the origin in the form of linear regressions. The variances about the calibration curves did not differ significantly (p greater than 0.05), while the calibration slopes for the diluents differed significantly (p less than 0.001). A standard serum solution was analyzed with the use of the eight diluents and the mean results did not differ significantly (p greater than 0.05). The % coefficient of variation varied from 0.8 to 2.0 and the percent recovery ranged from 95.5 to 102.5. The 99% confidence interval (CI) ranged from 0.02 to 0.09. Since conventional CIs do not take into account the random error of the calibration curve, the inverse CI were also calculated for each diluent. On both the conventional estimates and on the inverse CI, strontium chloride gave the best results, but only marginally in view of the interassay variability of approximately 1%.

Interrelationships among thiazide diuretics and calcium, magnesium, sodium, and potassium balance in normal and hypertensive man.

The benzothiadiazide diuretics are known to cause magnesium and potassium wasting and retention of calcium and uric acid. The effect of magnesium replacement on diuretic-induced changes in sodium, potassium, calcium, and magnesium balance, weight, and blood pressure was studied in 12 normal subjects and 13 hypertensive patients to determine whether oral magnesium would reduce thiazide-induced kaliuresis. The groups differed in their response to diuresis in that the normotensive subjects did not show a fall in blood pressure (despite an equivalent weight loss), returned to a state of sodium balance earlier, and developed a greater net negative potassium balance over 12 days of diuretic therapy. Both groups displayed calcium and uric acid retention and magnesium wasting during diuretic therapy. The addition of oral magnesium replacement during diuretic therapy had no effect on any measured values beyond that seen in subjects who took diuretics without magnesium replacement. Thus, magnesium replacement did not reduce urinary potassium loss. However, urinary calcium losses increased when magnesium was given to subjects who were not receiving diuretics. The data provide the first report that small doses of oral magnesium enhance calcium excretion in hypertensive subjects.

Changes in serum and sweat magnesium levels during work in the heat.

Serial changes in serum magnesium (Mg2+) were assessed in unacclimatized males during treadmill exercise in a hot (49 degrees/27 degrees C, dry/wet bulb) environment. Eight subjects walked at 5.6 km/h on a 0% grade, and at 90 min of exercise had a mean heart rate of increase of 70 plus or minus 5 (S.E.) beats/min, rise in rectal temperature of 2.1 degrees plus or minus 0.1 degrees C, and a weight loss of 2.07 plus or minus 0.10 kg. There was a significant (p less than 0.01) decrease in mean serum Mg2+ concentration (control: 1.87 plus or minus 0.06 mEq/I; 45 min: 1.81 plus or minus 0.07; 90 min: 1.72 plus or minus 0.08). The Mg2+ concentration in sweat samples collected over 90 min of work in the heat averaged 0.28 mEq/I (range 0.13 to 0.45). Thus, in normal man, exercise in an hot, dry environment resulted in a fall in serum magnesium which was not wholly explicable on the basis of sweat loss of this ion.