Morning magnesiuria: relation to age and sex.

Magnesium, calcium and creatinine concentration were assessed in the morning urine sample of 1710 subjects randomly selected from the population register in the Czech Republic: children aged 6, 10 and 13 years old and adults in age groups 18-35 years, 36-50 years, and 51-65 years of adults. The groups comprised 911 females and 799 males. There was a marked impact of age on the urinary magnesium concentration in both sexes, the concentration declining with advancing age. The child groups differed significantly from the adults. The urinary magnesium/creatinine ratio declined with age with the exception of the oldest group. The urinary calcium concentration did not change significantly with age in women or men. There was a weak age dependence in the calcium/creatinine ratio.