Vitamin D insufficiency and the blunted PTH response in established osteoporosis: the role of magnesium deficiency
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Vitamin D insufficiency is common, however within individuals, not all manifest the biochemical effects of PTH excess. This further extends to patients with established osteoporosis. The mechanism underlying the blunted PTH response is unclear but may be related to magnesium (Mg) deficiency. The aims of this study were to compare in patients with established osteoporosis and differing degrees of vitamin D and PTH status : (1) the presence of Mg deficiency using the standard Mg loading test (2) evaluate the effects of Mg loading on the calcium-PTH endocrine axis (3) determine the effects of oral, short term Mg supplementation on the calcium-PTH endocrine axis and bone turnover.
30 patients (10 women in 3 groups) were evaluated prospectively measuring calcium, PTH, Mg retention (Mg loading test), dietary nutrient intake (calcium, vitamin D, Mg) and bone turnover markers (serum CTX & P1CP). Multivariate analysis controlling for potential confounding baseline variable was undertaken for the measured outcomes.
All subjects, within the low vitamin D and low PTH group following the magnesium loading test had evidence of Mg depletion [mean(SD) retention 70.3%(12.5)] and showed an increase in calcium 0.06(0.01) mmol/l [95% CI 0.03, 0.09, p=0.007], together with a rise in PTH 13.3 ng/l (4.5) [95% CI 3.2, 23.4, p=0.016] compared to baseline. Following oral supplementation bone turnover increased: CTX 0.16 (0.06) mcg/l [95%CI 0.01, 0.32 p=0.047]; P1CP 13.1 (5.7) mcg/l [95% CI 0.29, 26.6 p=0.049]. In subjects with a low vitamin D and raised PTH mean retention was 55.9%(14.8) and in the vitamin replete group 36.1%(14.4), with little change in both acute markers of calcium homeostasis and bone turnover markers following both the loading test and oral supplementation.
This study confirms that in patients with established osteoporosis, there is also a distinct group with a low vitamin D and a blunted PTH level and that Mg deficiency (as measured by the Mg loading test) is an important contributing factor.
KeywordsFunctional hypoparathyroidism Magnesium Osteoporosis Secondary hyperparathyroidism Vitamin D
The authors are grateful to the research nurses in the Metabolic Unit for their help in collating data. We are also grateful to Isabel Fowler in the Department of Clinical Chemistry for her support in preparing/analysing some of the biochemical samples, and Vincent Crosby for his advice on undertaking the Mg studies.
- 3.Melin AL, Wilske J, Ringertz H, Sääf M (2000) Vitamin D status, parathyroid function and femoral bone density in an elderly Swedish population living at home. Aging Clin Exp Res 11:200–207Google Scholar
- 12.Lamberg-Allardt C, von Knorring J, Slatis P, Holmstrom T (1988) Vitamin D status and concentrations of serum vitamin D metabolites and osteocalcin in elderly patients with femoral neck fracture: a follow-up study. Eur J Clin Nutr 43:355–361Google Scholar
- 15.Rao DS, Kleerekoper M, Rogers M, Frame B, Parfitt A (1984) Is gastrectomy a risk factor for osteoporosis? In: Christiansen C (ed) Osteoporosis. Glostrup Hospital, Denmark 775–777Google Scholar
- 19.Rude RK, Oldham SB, Singer FR (1986) Functional hypoparathyroidism and parathyroid hormone end-organ resistance in human Mg deficiency. Clin Endocrinol 5:209–224Google Scholar
- 24.Cohen L, Laor A, Kitzes R (1983) Magnesium malabsorption in postmenopausal osteoporosis. Magnesium 2:271–274Google Scholar
- 26.Siener R, Hesse A (1995) Influence of a mixed and a vegetarian diet on urinary Mg excretion and concentration. B J Nutr 54:553–559Google Scholar
- 30.Eskiyurt N, Akt S, Aydogan A, Aksac B, Sen N, Akyuz G, Oncel A (2000) The evaluation of the effects of calcium, magnesium and vitamin D derivatives on bone density and biochemical markers of bone turnover in cases of postmenopausal osteoporosis. Osteop Int 3(S62):23Google Scholar
- 31.Rude RK, Oldham SB, Sharp CF Jr, Singer FR (1978) Parathyroid hormone secretion in Mg deficiency. J Clin Endo Metab 47:800–806Google Scholar
- 32.Medalle R, Waterhouse C, Hahn TJ (1986) Vitamin D resistance in Mg deficiency. Am J Clin Nutr 29:854–858Google Scholar