Overnight suppression of parathyroid hormone and bone resorption markers by active absorbable algae calcium. A double-blind crossover study

Conjugated linoleic acid is related to bone mineral density but does not affect parathyroid hormone in men

The relationships between conjugated linoleic acid (CLA) status, bone, body composition, and the effect of CLA on calciotropic hormones are unclear. A cross-sectional study was designed to examine the association between c9, t11 CLA status in erythrocyte membranes (RBC) and body composition. This preceded a dose-response trial investigating if c9, t11 CLA affected parathyroid hormone (PTH). It was hypothesized that (1) higher c9, t11 CLA status in RBC will be associated with a lower fat and higher bone mass and that (2) PTH will be reduced by 30% after supplementation of c9, t11 CLA. Fifty-four men (age, 19-53 years) were included in the cross-sectional analysis, of which 31 were studied in the dose-response trial and randomized to 1 of 3 groups: placebo (n = 10), 1.5 g/d (n = 11), or 3.0 g/d (n = 10) of c9, t11 CLA for 16 weeks. Men with RBC c9, t11 CLA status above the median had higher whole body bone mineral density (BMD) (1.359 ± 0.024 vs 1.287 ± 0.023 g/cm(2); P = .04) and whole body lean mass (WBL) percentage (78.8% ± 0.9% vs 75.3% ± 1.0%; P = .01), whereas body mass index (24.8 ± 0.5 kg/m(2) vs 27.3 ± 0.9 kg/m(2); P = .01) and whole body fat mass percentage (17.3% ± 0.9% vs 21.3% ± 1.1%; P = .007) were lower. In regression analysis, RBC c9, t11 CLA status accounted for a significant proportion (r(2) = 0.10) of the variation in whole body BMD (P = .03). There were no time or treatment differences among any bone or biomarkers of bone metabolism including PTH. These findings indicate that RBC c9, t11 CLA status, a reflection of long-term (~4 months) dietary CLA intake, positively relates to BMD. However, c9, t11 CLA supplementation does not appear to affect PTH in healthy men.

The physiology of the circadian rhythm of parathyroid hormone and its potential as a treatment for osteoporosis

PURPOSE OF REVIEW

A circadian rhythm exists for parathyroid hormone, with a biphasic pattern showing a late afternoon/early evening rise and fall and a broader, longer-lasting increase late evening/early morning reaching nadir mid-morning. This review explores the characteristics of the circadian rhythm, factors regulating the rhythm and its role in bone metabolism.

RECENT FINDINGS

Gender differences exist in the circadian rhythm for parathyroid hormone. Ageing in women alters the response to calcium infusion, increasing the suppression of parathyroid hormone secretion and decreasing bone resorption. There is no difference between young and elderly men in the parathyroid hormone response to calcium infusion. Loop diuretic ingestion alters the parathyroid hormone circadian rhythm reflecting loop diuretic effects on phosphate and calcium metabolism. Adult growth hormone deficiency alters parathyroid hormone secretion and end organ sensitivity, but the circadian rhythm is retained. Growth hormone replacement therapy enhances the parathyroid hormone circadian rhythm and increases end organ responses. Exogenous parathyroid hormone (1-34) and (1-84) administered by daily injection has an anabolic effect on bone, increasing bone mass and decreasing fracture. Calcilytic drugs stimulate and calcimimetic drugs suppress parathyroid hormone secretion and have been used to treat disorders of bone metabolism.

SUMMARY

The circadian nature of parathyroid hormone secretion is confirmed by many publications. The underlying rhythm is endogenous. Life style factors and nutritional intake modulate the pattern of secretion. Direct association with bone resorption and formation is tentative. It is suggested that acute changes in these rhythms have little effect on resorption, but longer-term manipulation of parathyroid hormone secretion alters bone cell function. Growth hormone therapy in adult deficiency increases parathyroid hormone activity, indicating growth hormone may have therapeutic potential for osteoporosis. Manipulation of the endogenous parathyroid hormone rhythm, using timed supplements of phosphate or calcium or by calcilytic and calcimimetic molecules, offers a novel approach to osteoporosis treatment.

Mineral water as a source of dietary calcium: acute effects on parathyroid function and bone resorption in young men

BACKGROUND

Calcium is a major component of mineralized tissues and is required for normal growth and maintenance of bone. Epidemiologic studies showed that a large percentage of the population fails to meet the currently recommended guidelines for optimal calcium intake.

OBJECTIVE

The present study was designed to determine whether high-calcium mineral water is an efficient additional source of dietary calcium.

DESIGN

Twelve healthy young men (mean +/- SD age: 21.1 +/- 1.2 y) ingested in a randomized order either 0.5 L of a mineral water containing 344 mg Ca/L or 0.5 L of a mineral water with a very low concentration of calcium (<10 mg/L) as a control. Blood samples were drawn before and 1, 2, 3, and 4 h after intake of the water. Urine was collected for 2 h before and every 2 h for 4 h after ingestion of the water. Serum concentrations of intact parathyroid hormone (iPTH) and serum concentrations and urinary excretion of a recently developed biochemical marker of bone resorption, type 1 collagen cross-linked C-telopeptide (CTx), were measured.

RESULTS

Serum iPTH was significantly (P < 0.002) lower after ingestion of high-calcium water than after ingestion of the control. There was a significant (P = 0.01) progressive decrease in urinary CTx after ingestion of the high-calcium water, whereas after ingestion of low-calcium water the changes were modest and not significant. The fall in serum CTx concentrations was 34.7% 3 h after ingestion of high-calcium water, compared with 17.6% with the control. The decreases in serum CTx concentrations were significantly (P < 0.05) lower 1, 2, 3, and 4 h after ingestion of high-calcium water than after ingestion of the control.

CONCLUSION

The present study showed that one oral intake of water containing a very moderate dose of calcium (172 mg) acutely inhibited iPTH secretion and bone resorption.

Adverse effects of an active fragment of parathyroid hormone on rat hippocampal organotypic cultures

Adverse effects of an active fragment of parathyroid hormone (PTH(1 - 34)), a blood Ca(2+) level-regulating hormone, were examined using rat hippocampal slices in organotypic culture. Exposure of cultured slice preparations to 0.1 microM PTH(1 - 34) for 60 min resulted in a gradual increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)); this effect was most obvious in the apical dendritic region of CA1 subfield. When PTH(1 - 34) at a lower concentration (1 nM) was added to the culture medium and its toxic effects examined using a propidium iodide intercalation method, significant toxicity was seen 3 days after exposure and increased with time. Cells in the CA1 region seemed more vulnerable to the hormone than cells in other regions. At 1 week of exposure, the toxic effects were dose-dependent over the range of 0.1 pM to 0.1 microM, the minimum effective dose being 10 pM. The adverse effects were not induced either by the inactive fragment, PTH(39 - 84), or by an active fragment of PTH-related peptide (PTHrP(1 - 34)), an intrinsic ligand of the brain PTH receptor. The PTH(1 - 34)-induced adverse effects were significantly inhibited by co-administration of 10 microM nifedipine, an L-type Ca(2+) channel blocker, but not by co-administration of blockers of the other types of Ca(2+) channel. The present study demonstrates that sustained high levels of PTH in the brain might cause degeneration of specific brain regions due to Ca(2+) overloading via activation of dihydropyridine-sensitive Ca(2+) channels, and suggests that PTH may be a risk factor for senile dementia. British Journal of Pharmacology (2000) 129, 21 - 28

The roles of calcium and vitamin D in the prevention of osteoporosis

Calcium supplementation produces small beneficial effects on bone mass throughout postmenopausal life and may reduce fracture rates by more than this change would predict--possibly by as much as 50%. There is little reason to use vitamin D in young populations that are replete in this compound, but in the elderly at risk of vitamin D deficiency, there is now evidence of significant reductions in nonvertebral fracture rates from physiologic replacement regimens. Some of the most substantial reductions in fracture rates have been found with combined therapy with calcium and vitamin D, and in these protocols it is not clear which is the principal active agent or whether, in fact, the combination is necessary for optimal antifracture efficacy.