Chronobiologic observations of calcium and magnesium in the elderly.

Sixty-two elderly men (average age 75 +/- 6 yrs) and 85 elderly women (average age 79 +/- 8 yrs) institutionalized at Berceni Clinical Hospital, Bucharest, Romania, were investigated over a 24 hour span, some of them repeatedly, leading to a total of 269 profiles. The subjects were studied in 12 subgroups spread over all four seasons. Total serum calcium, inorganic phosphate, total protein, albumin and urinary calcium and magnesium were determined. Circadian rhythms were found in all variables. There were statistically significant phase differences between serum calcium, total protein and serum albumin speaking against the serum protein rhythm (or circadian variations in hydration) being responsible for the circadian rhythm in total serum calcium. There are phase differences between the elderly (and young) subjects studied in Romania and several series reported from Germany and the USA. Circadian and circannual variations were found for urinary calcium and magnesium excretion, with maximum in fall and low values during summer. The peak excretion thus follows, rather than coincides, with the time of maximum sun exposure. The elderly subjects studied in Romania show a relatively low circadian (24-hour) mean calcium excretion, and the circadian acrophase in the elderly occurs during the night hours in keeping with the acrophase shift found in elderly subjects in urine volume and other electrolytes.