MAJOR MINERAL CONCENTRATIONS IN HUMAN-MILK DO NOT CHANGE AFTER MAXIMAL EXERCISE TESTING

Fourteen healthy, lactating women (aged 25-38 y and between 2 and 8 mo postpartum) participated in both a maximal graded exercise test and a 30-min rest period to determine the influence of exercise on the conc entration of selected milk minerals and electrolytes. Treatment order was randomized and treatments were conducted on different days. Milk w as expressed before treatment and at 10, 30, and 60 min postexercise o r after the rest period. Milk was wet-ashed by using nitric and sulfur ic acids. Aliquots were analyzed for total phosphorus concentration by colorimetric assay and for calcium, magnesium, sodium, and potassium by inductively coupled plasma atomic emission spectrophotometry. Basel ine mineral concentrations were not significantly different (P < 0.05) . Repeated expression of milk at 10, 30, and 60 min did not show signi ficantly altered mineral concentrations (P > 0.05). Interwoman variati on was responsible for most of the variation in mineral concentrations . A portion of this may be explained by the variation in stage of lact ation, which is known to affect mineral composition. Stage of lactatio n was inversely correlated with concentration of calcium, total phosph orus, magnesium, and sodium (P < 0.05). In conclusion, maximal exercis e did not alter concentrations of phosphorus, calcium, magnesium, pota ssium, or sodium in milk. Thus, with respect to mineral concentrations in milk, there is no contraindication for exercise during lactation.