The relative bioavailability of zinc (RBAZ) in corn, rice, wheat and legumes was determined by the ratio of net weight gains a 6 ppm of added zinc, a measure derived from sigmoidal curves for weight gain estimated by a non-linear, least-squares curve fitting computer program. Each food was prepared as for human consumption, incorporated into a semi-purified diet to provide varying levels of zinc and fed to weanling rats. Among cereals, whole corn and brown rice had low RBAZ (0.58 or less), while whole wheat flour and unleavened whole wheat bread had medium values (0.63-0.74). Refined cereal grains, such as white flour, leavened and unleavened white bread and white rice, had high RBAZ (0.89-1.08) as did leavened whole wheat bread (1.04). Of the legumes, lima beans had a high RBAZ (0.84) while white beans had a medium value (0.74). Phytic acid content of the foods, but not neutral-detergent fiber content, appeared to be inversely related to RBAZ, more so among the cereals than with the legumes.

In a single case study of a moderately trained, healthy man, physiologic changes during a marathon are reported. Blood was drawn prior to the race, at 1 hour and 2 hours into the race, at the end of the race, and after 1 hour of recovery. By 1 hour into the race, norepinephrine, epinephrine, and dopamine had increased nearly nine-fold, two-fold and five-fold, respectively. After 1 hour of recovery, epinephrine had returned to the pre-race value but norepinephrine and dopamine were still elevated. Cortisol increased gradually and was more than doubled by the end of the race. It was still elevated after 1 hour of recovery. White blood cells gradually increased, reaching their maximum value at the end of the race; a four-to-five-fold increase. Thromboxane B2, which had an inverse relationship to serum magnesium, was below the pre-race value for the first 2 hours but increased nine-fold by the end of the race. Serum magnesium increased from 1.44 meq/l to 1.68 meq/l at 2 hours into the marathon, dropped to 1.07 meq/l by the end of the race, and returned to its pre-race value by 1 hour of recovery. The decrease in serum magnesium at the end of the race may be associated with increased plasma free fatty acid levels.

Functional biological markers or biomarkers are now available for many nutrients which are used as nutritional status markers. Most sources of these biomarkers are products or precursors of enzymatic processes that can be measured in serum and plasma. At this time measurements of total or ionized magnesium (Mg) in serum, plasma, cellular components, urine or Mg retention from a load test are performed, but they may not always reflect Mg nutritional status. Biomarkers for Mg are needed which would reflect changes in biochemical processes where Mg is involved. Biomarkers for Mg need to be identified and evaluated in both animals and humans, with a determination of possible factors that may affect the reaction and biomarker concentrations. Some possible biomarkers for Mg include the following: Na/K ATPase, thromboxane B2, C-reactive protein, and endothelin-1. Other possible biomarkers for Mg need to be identified.

Increased temperature can increase magnesium sweat losses, which may not be compensated by diet or water intake. Climate relationships to these diseases need further investigation.