Dietary magnesium deficiency decreases plasma melatonin in rats.

It has been postulated that Mg depletion is associated with decreased melatonin. Exogenous magnesium (Mg) has been found to increase the activity of serotonin N-acetyltransferase, an enzyme in the pathway for melatonin synthesis; but no data have been found on the effect of Mg deficiency on plasma melatonin. This pilot study examined the effect of a dietary Mg deficiency on plasma melatonin in male, Sprague-Dawley rats. Weanling rats were placed on a Mg-deficient (150 ppm) or a Mg-adequate (1000 ppm) diets for four weeks, after which they were sacrificed 4, 5 or 7 hours into the dark cycle. Plasma was assayed for melatonin concentrations. A significant decrease (p = 0.0101) occurred in mean (+/- SEM) plasma melatonin levels of the Mg-deficient animals (50 +/- 6.4 pg/mL) when compared to the Mg-adequate animals (75 +/- 6.6 pg/mL). There was no obvious phase shift in the melatonin profile of the Mg-deficient animals when compared to the Mg-adequate animals.