Calcium Metabolism Evaluated by 47Ca kinetics: Estimation of Dermal Calcium Loss

Abstract

Seventy-seven calcium balance and 47Ca turnover studies were performed in normal volunteers (n = 15) and in patients with osteoporosis (n = 12), primary hyperparathyroidism (n = 8), osteogenesis imperfecta (n = 5), medullary carcinoma of the thyroid (n = 4), thyrotoxicosis (n = 2) and intestinal bypass for obesity (n = 11). After intravenous injection of 20 microCi of 47Ca two retention curves of 47Ca were obtained: R1(t) directly measured on a whole-body counter and R2(t) calculated from the cumulated daily excretions of 47Ca in urine and faeces. The data were fitted to a modification of the continuously expanding exchangeable calcium pool model. Dermal calcium loss was estimated from the serum 47Ca specific radioactivity curve and the constantly increasing difference between the two retention curves. The median dermal calcium loss in 77 studies was 1.50 mmol 24 h-1 1.73 m-2 (range 0.13-4.60). The dermal calcium loss might be overestimated by redistribution of tracer or by eventual insufficient collection of urine and faeces. The possible influences of these errors have been evaluated. Patients with primary hyperparathyroidism had a greater (P less than 0.02) dermal calcium loss (2.64 mmol; range 0.80-4.50) than a control group (1.38 mmol; range 1.25-2.34).

The calcium controversy

“…On Western diets, faecalloss due to unreabsorbed digestive juice calcium never falls below some 150 mg daily [13J; urinary loss never falls below about 100 mg daily [14J; dermal los ses amount to about 40 mg daily [15]. These significant obligatory losses distinguish calcium from other minerals such as sodium, potassium and rnagnesium that can be largely eliminated from the faeces and urine in nutritional deficiency states [16].…”

Effect of vitamin D treatment in hypoparathyroid patients: a study on calcium, phosphate and magnesium homeostasis

“…Four of the patients suffered from idiopathic HP, 11 patients had postsurgical HP with a mean (and median) time since surgery of 20 years (range years). The diagnosis was based on low serum PTH levels on several occasions, relief from muscular spasms by treatment with calcium and vitamin D and inability to maintain normal serum calcium levels, and a rapid return of symptoms when treatment was withdrawn.…”

Triiodothyronine increases calcium loss in a bed rest antigravity model for space flight

“…Dermal calcium losses were assumed to be constant at 60 mg/d for both groups based on the results of the 47 Ca method of Charles et al [22] and Jensen et al [10,23,24].…”