Assessment of bioavailability of Mg from Mg citrate and Mg oxide by measuring urinary excretion in Mg-saturated subjects.

Background: Low magnesium (Mg) levels are linked to many diseases. Studies suggest that organic salts of Mg are more readily bioavailable than its oxide or inorganic salts used for supplements production. Unfortunately, the plethora of variables in the previous study designs complicates the making of any clear and reliable conclusions.

Methods: 14 healthy males were supplemented for five days with 400 mg Mg to saturate Mg pools before intake of the test products. Bioavailability of 400 mg Mg from Mg citrate (MgC) and Mg oxide (MgO) after single-dose administration was assessed by measuring renal Mg excretion in 24-h urine and blood plasma [Mg] at time points 0, 2, 4, 8, and 24 h.

Results: Single-dose MgC supplementation led to a significant (P < 0.05) increase in 24 h urinary Mg excretion, but this was not significant following MgO. Plasma [Mg] was also significantly higher for MgC than for MgO at 4 h (P < 0.05) and 8 h (P < 0.05). Compared with baseline levels, MgC supplementation showed a significant increase in plasma [Mg] at all time points, in contrast to MgO.

Conclusions: MgC shows higher bioavailability compared with MgO. Furthermore, urinary Mg excretion should be determined as the primary endpoint of Mg bioavailability studies.