Circaannual rhythms and interactions of vitamin D metabolites, parathyroid hormone, and biochemical markers of skeletal homeostasis: a prospective study

Seasonality of vitamin D status and bone turnover in patients with Crohn's disease

BACKGROUND

While winter-time vitamin D deficiency has been well-documented in Crohn's disease patients, less is known about vitamin D status during summertime and whether a seasonal variation exists in bone turnover.

AIMS

To compare vitamin D status and bone turnover markers in Crohn's disease patients with age- and sex-matched controls during late-summer and late-winter.

SUBJECTS

Crohn's disease patients (n = 44; mean age 36.9 years, currently in remission) and matched controls (n = 44) were recruited from Cork University Hospital and Cork City area, respectively.

METHODS

Bloods were analysed for 25-hydroxyvitamin D, parathyroid hormone, bone-specific alkaline phosphatase, osteocalcin and urine analysed for N-telopeptides of type 1 collagen.

RESULTS

Serum 25-hydroxyvitamin D concentrations were significantly (P < 0.003) lower in Crohn's disease patients than in control subjects during both seasons. In Crohn's disease patients, serum 25-hydroxyvitamin D concentrations were lower (P < 0.0001) whereas serum parathyroid hormone, osteocalcin and bone-specific alkaline phosphatase and urinary N-telopeptides of type 1 collagen levels were higher (P < 0.001) during late-winter than late-summer.

CONCLUSION

There were notable seasonal variations in vitamin D status and bone turnover markers in Crohn's disease patients. The impact of winter decline in vitamin D status and increase in bone turnover on long-term risk of osteopenia/osteoporosis in Crohn's disease patients is unclear.

Structural organization and biological relevance of oscillatory parathyroid hormone secretion

Parathyroid gland secretory activity exhibits seasonal and circadian fluctuations, which are in synchrony with changes in serum calcium, phosphate, and bone turnover. In addition, an ultradian rhythm exists, which comprises seven pulses per hour, accounts for 30% of basal parathyroid hormone (PTH) release, and is highly sensitive to changes in ionized calcium. Acute hypocalcemia induces a selective, severalfold increase in pulse frequency and amplitude, whereas hypercalcemia suppresses the pulsatile secretion component, as does prolonged calcitriol therapy. Chronic renal failure is associated with a GFR dependent decrease in metabolic PTH clearance accounting for a two- to threefold increase in plasma PTH concentrations, a consistent increase of PTH burst mass and frequency, and a markedly reduced capacity to counteract changes in ionized calcium by modulation of pulsatile PTH release. Continuous PTH excess destroys bone, whereas intermittent administration of pharmacological doses of PTH improves bone morphology and strength in experimental and clinical settings. The molecular mechanisms of the exposure pattern dependent, contrasting biological effects of PTH may involve differential regulation of osteoblastic G protein signaling feedback circuits. In this context, calcimimetic and calcilytic agents are promising new therapeutic tools allowing for tight control of plasma PTH and restoration of circadian PTH rhythmicity.

Nutritional rickets: deficiency of vitamin D, calcium, or both?

Nutritional rickets remains a public health problem in many countries, despite dramatic declines in the prevalence of the condition in many developed countries since the discoveries of vitamin D and the role of ultraviolet light in prevention. The disease continues to be problematic among infants in many communities, especially among infants who are exclusively breast-fed, infants and children of dark-skinned immigrants living in temperate climates, infants and their mothers in the Middle East, and infants and children in many developing countries in the tropics and subtropics, such as Nigeria, Ethiopia, Yemen, and Bangladesh. Vitamin D deficiency remains the major cause of rickets among young infants in most countries, because breast milk is low in vitamin D and its metabolites and social and religious customs and/or climatic conditions often prevent adequate ultraviolet light exposure. In sunny countries such as Nigeria, South Africa, and Bangladesh, such factors do not apply. Studies indicated that the disease occurs among older toddlers and children and probably is attributable to low dietary calcium intakes, which are characteristic of cereal-based diets with limited variety and little access to dairy products. In such situations, calcium supplements alone result in healing of the bone disease. Studies among Asian children and African American toddlers suggested that low dietary calcium intakes result in increased catabolism of vitamin D and the development of vitamin D deficiency and rickets. Dietary calcium deficiency and vitamin D deficiency represent 2 ends of the spectrum for the pathogenesis of nutritional rickets, with a combination of the 2 in the middle.

Assessment of Urinary Bone Markers for Monitoring Treatment of Osteoporosis

Background: The usefulness of urinary markers of bone turnover in monitoring therapy depends on their within-person variability compared with their responses to therapy. The aim of this study was to assess the performance of two such markers on this basis.

Methods: We measured variation, during a whole year, of cross-linked N-terminal telopeptide of collagen I (NTx) and urinary deoxypyridinoline (DPD) as ratios to creatinine concentration and after log-transformation of the ratios in untreated women stratified into three bone density classes, of which the lowest was osteoporotic. We also measured changes in bone mineral density at the lumbar spine (LSBMD) and hip (FNBMD) in untreated women with normal bones and in those with moderate osteopenia and calculated the reference change value (RCV; or least significant change) at P &lt;0.05 for all of these measures. We made the same measurements on women treated with bisphosphonates, estrogen replacement (HRT), or calcium and examined their individual responses to treatment compared with RCV.

Results: After 12 months on bisphosphonates, LSBMD changed more than RCV (2.55%) in 47% of women compared with 44% of those on HRT and 13% of those on calcium. Response of FNBMD was less. Log NTx (RCV= −28%) responded to bisphosphonates in 78%, regardless of BMD, but less often to HRT (67%). Log DPD (RCV= −30%) responded to bisphosphonates less frequently (31% at 12 months).

Conclusions: NTx has advantages over DPD in monitoring therapy for osteoporosis when mailed urine samples are used.

Supplementation with oral vitamin D3 and calcium during winter prevents seasonal bone loss: a randomized controlled open-label prospective trial

Bone metabolism follows a seasonal pattern with high bone turnover and bone loss during the winter. In a randomized, open-label 2-year sequential follow-up study of 55 healthy adults, we found that supplementation with oral vitamin D3 and calcium during winter abolished seasonal changes in calciotropic hormones and markers of bone turnover and led to an increase in BMD. Supplementation with oral vitamin D3 and calcium during the winter months seems to counteract the effects of seasonal changes in vitamin D and thus may be beneficial as a primary prevention strategy for age-related bone loss.

INTRODUCTION

Bone metabolism follows a seasonal pattern characterized by high bone turnover and bone loss during winter. We investigated whether wintertime supplementation with oral vitamin D3 and calcium had beneficial effects on the circannual changes in bone turnover and bone mass.

MATERIALS AND METHODS

This prospective study comprised an initial observation period of 12 months ("year 1"), followed by an intervention during parts of year 2. Fifty-five healthy subjects living in southwestern Germany (latitude, 49.5 degrees N) were randomized into two groups: 30 subjects were assigned to the treatment group and received oral cholecalciferol (500 IU/day) and calcium (500 mg/day) during the winter months of year 2 (October-April), while 25 subjects assigned to the control group obtained no supplements. Primary endpoints were changes in calciotropic hormones [serum 25(OH)D, 1,25(OH)2D, and parathyroid hormone], markers of bone formation (serum bone-specific alkaline phosphatase) and of bone resorption (urinary pyridinoline and deoxypyridinoline), and changes in lumbar spine and femoral neck BMD.

RESULTS

Forty-three subjects completed the study. During year 1, calciotropic hormones, markers of bone turnover, and BMD varied by season in both groups. During the winter months of year 1, bone turnover was significantly accelerated, and lumbar spine and femoral BMD declined by 0.3-0.9%. In year 2, seasonal changes in calciotropic hormones and markers of bone turnover were either reversed or abolished in the intervention group while unchanged in the control cohort. In the subjects receiving oral vitamin D3 and calcium, lumbar and femoral BMD increased significantly (lumbar spine: +0.8%, p = 0.04 versus year 1; femoral neck: +0.1%, p = 0.05 versus year 1), whereas controls continued to lose bone (intervention group versus control group: lumbar spine, p = 0.03; femoral neck, p = 0.05).

CONCLUSIONS

Supplementation with oral vitamin D3 and calcium during winter prevents seasonal changes in bone turnover and bone loss in healthy adults. It seems conceivable that annually recurring cycles of low vitamin D and mild secondary hyperparathyroidism during the winter months contributes, at least in part and over many years, to age-related bone loss. Supplementation with low-dose oral vitamin D3 and calcium during winter may be an efficient and inexpensive strategy for the primary prevention of bone loss in northern latitudes.

Daily rhythm of circulating fat soluble vitamin concentration (A, D, E and K) in the horse

Background

Many physiological processes of mammalian species exhibit daily rhythmicity. An intrinsic relationship exists between fat soluble vitamins (A, D, E and K) and several body functions. Few investigations on the rhythmic pattern of vitamins in domestic animals have been carried out. The present study evaluated the circadian rhythmicity of fat soluble vitamins in the horse.

Methods

Blood samples from 5 Thoroughbred mares were collected at four-hour intervals over a 48-hour period (starting at 8:00 hours on day 1 and finishing at 4:00 on day 2) via an intravenous cannula inserted into the jugular vein. Fat soluble vitamin concentration in the serum (A, D, E and K) was measured by HPLC. One-way repeated measures analysis of variance (ANOVA) was used to determine significant differences. p values < 0.05 were considered statistically significant.

Results

ANOVA showed a highly significant effect of time in all the horses for the vitamins studied (p < 0.0001). The application of the periodic model and the statistical analysis of the "Cosinor" enabled us to define the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring: all the studied vitamins showed diurnal acrophases with values between 15:16 and 18:08 hours.

Conclusion

Fat soluble vitamins exhibit daily rhythmicity with diurnal peak. Further investigations could help optimize the use of these substances according to their circadian (or other) rhythms.

Circadian variation in biochemical markers of bone cell activity and insulin-like growth factor-I in two-year-old horses

Studies in humans have found circadian changes to be one of the most important sources of controllable preanalytical variability when evaluating bone cell activity using biochemical markers. It remains unclear whether similar circadian changes influence bone marker concentrations in the horse. The aim of this study was to characterize changes in serum concentrations of three biochemical markers of bone cell activity over a 24-h period in six 2-yr-old Thoroughbred mares, and to determine circadian variability in IGF-I, which regulates bone turnover. Three bone markers were measured in serum: osteocalcin, a marker of bone formation, the carboxy-terminal propeptide of type-I collagen (a marker of bone formation), and the carboxy-terminal telopeptide of type-I collagen (a marker of bone resorption). Data were analyzed using the cosinor technique, which fits a 24-h cycle to each dataset. A significant circadian rhythm was observed for osteocalcin (P = 0.028), with an estimated amplitude of 7.6% of the mean (95% confidence interval 1.3% to 16.3%), and an estimated peak time of 0900. However, the observed rhythm for the carboxy-terminal telopeptide of type-I collagen (amplitude = 7.4%) was not significant (P = 0.067), and there were no significant changes in concentrations of the carboxy-terminal propeptide of type-I collagen over the 24-h study period (P = 0.44). There was a small but significant circadian rhythm for IGF-I (P = 0.04), with an estimated amplitude of 3.4% (95% confidence interval 0.2 to 7.1%) and peak at 1730. Further studies are now required to determine the potential association between circadian changes in IGF-I and osteocalcin in the horse. Although no significant circadian variation was found in concentrations of the car-boxy-terminal propeptide of type-I collagen and the carboxy-terminal telopeptide of type-I collagen, this may in part be a result of the age of the animals that were still skeletally immature. Future studies should aim to determine whether these markers develop a circadian rhythm at a later age when growth is complete. In the meantime, consistency in time of sampling should continue to be considered best practice when measuring biochemical markers of bone turnover in the horse.

Beyond deficiency: potential benefits of increased intakes of vitamin K for bone and vascular health

Vitamin K is well known for its role in the synthesis of a number of blood coagulation factors. During recent years vitamin K-dependent proteins were discovered to be of vital importance for bone and vascular health. Recommendations for dietary vitamin K intake have been made on the basis of the hepatic requirements for the synthesis of blood coagulation factors. Accumulating evidence suggests that the requirements for other functions than blood coagulation may be higher. This paper is the result of a closed workshop (Paris, November 2002) in which a number of European vitamin K experts reviewed the available data and formulated their standpoint with respect to recommended dietary vitamin K intake and the use of vitamin K-containing supplements.

Seasonal variation in bone density in postmenopausal women

We investigated seasonal variation in bone density by cross-sectional designs in two large cohorts of women (N = 2337) in Sweden. One cohort was strictly population-based (all 75 yr old, N = 1044), and one cohort was patient-based (age > or = 55 yr, mean age 68, N = 1293). Each woman was assessed once and the inclusion was continuous throughout almost all days of the year. Bone mineral density (BMD) of the total body, hip, and lumbar spine was determined by means of dual X-ray absorptiometry (DXA). For both cohorts, the BMD was similar in those assessed during the period April-September compared to those assessed during the period October-March. On the other hand, when women who had been assessed during July-December were compared with women assessed during January-June, we found the BMD to be up to 5% lower during July-December in all skeletal regions in the population-based sample, and 4% lower at the Ward's triangle and trochanter in the patient-based sample. After correction for small differences in age and weight, women of both cohorts who had been assessed during July-December still had lower BMD at the hip compared with women assessed during January-June. In conclusion, we found no variation in bone density during the period April-September compared to the period October-March in these two cohorts of postmenopausal women. In elderly women living at a northern latitude, BMD may be a few percent lower during the period July-December compared to the period January-June.

Bone remodeling markers: assessment of fracture risk and fracture risk reduction

There is an increasing repertoire of laboratory tests available for assessing the bone remodeling process. Biochemical markers of bone remodeling can be measured in serum or urine, and have a number of potential roles in the management of fracture risk. Differences in remodeling between individuals might be related to fracture risk and could be used to target therapy. Change in remodeling with therapy could be related to fracture risk reduction and the choice of therapy could be influenced by knowledge of bone remodeling. Biochemical therapeutic monitoring may improve patient understanding and therapeutic adherence. The rate of bone remodeling is weakly predictive of fracture risk in individuals who are not receiving therapy; however, it is not clear whether this is independent of other risk factors. There is increasing evidence that change in bone mineral density does not explain fracture risk reduction with antiresorptive therapies, and that therapeutic benefit might be explained by change in bone turnover. Additional studies and information are required to allow these scientific advances to be translated into cost-effective and validated clinical protocols. Optimizing the precision and accuracy of bone turnover assessment remains an important priority.

Role of vitamin D and parathyroid hormone in the regulation of bone turnover and bone mass in men: the MINOS study

We investigated the role of vitamin D and of parathyroid hormone (PTH) in the regulation of bone mineral density (BMD), tone dimensions and seasonal variation of bone turnover in 881 men aged 19-85 years. Bone mineral content (BMC) and BMD of the lumbar spine, hip and whole body were measured with HOLOGIC 1000W and those of distal forearm with an OSTEOMETER DTX 100 device. Bone formation was evaluated using osteocalcin, bone alkaline phosphatase and N-terminal extension propeptide of type I collagen (PINP). Bone resorption was evaluated by 24-hour excretion of deoxypyridinoline and of C-terminal telopeptide of collagen type I. In young men (< 55 yrs) PTH level decreased with age (r = -0.18, P < 0.005) whereas 25-hydroxyvitamin D (25OHD) concentration was stable. In older men (> 55 years) 25OHD decreased whereas PTH increased with age (r = -0.27 and r = 0.21, P = 0.0001). In young men, 25OHD level varied with season but not PTH, biochemical markers of bone turnover nor BMD. In young men, 25OHD, but not PTH, was a significant determinant of BMC, cortical thickness and of biomechanical properties of the femoral neck. Biochemical bone markers and BMD were not correlated with PTH nor with 25OHD. In elderly men, winter levels of 25OHD were lowest whereas those of PTH, bone resorption markers and PINP were highest. After adjustment for age, body weight and season, biochemical markers of bone turnover were correlated with PTH. In elderly men, 25OHD and PTH were significant determinants of BMC, cortical thickness and of biomechanical parameters of the femoral neck. Men with vertebral deformities had lower concentrations of 25OHD, higher PTH levels and slightly elevated urinary excretion of biochemical markers of bone resorption compared with men without vertebral deformities. In conclusion, in young men, 25OHD discloses a seasonal variability in contrast to PTH and biochemical bone markers. In this group, 25OHD is a significant determinant of BMC and BMD but not of bone size. In elderly men, seasonal variation of 25OHD and PTH concentrations result in seasonal variation of bone resorption. In this group, both 25OHD and PTH are determinants of BMC and cortical thickness of the femoral neck and, consequently, of its mechanical parameters.

Absence of marked seasonal change in bone turnover: a longitudinal and multicenter cross-sectional study

The effect of season on bone turnover is controversial. No information is available on seasonality of new serum markers of bone resorption. In this study, we have been unable to confirm findings of a marked wintertime increase in bone formation and resorption within the general population. Seasonality was assessed by cosinor analysis.

INTRODUCTION

We investigated the effect of season on seven markers of bone turnover in a longitudinal study (six men and six premenopausal women; age, 24-44 years) and a separate large population-based multicenter European study (n = 2780 women, Osteoporosis and Ultrasound Study [OPUS]).

MATERIALS AND METHODS

Measurements included serum Crosslaps, procollagen type I N-terminal propeptide (PINP), osteocalcin (OC), and the N-telopeptide fragment of type I collagen in urine (NTX). Seasonality was assessed by cosinor analysis with Hotelling's T2 test.

RESULTS

Serum 25(OH) vitamin D showed a marked seasonal rhythm. There was no significant seasonal component for any marker of bone turnover in the longitudinal analysis (cosinor analysis, p > 0.05). The percentage of within subject variance accounted for by any seasonal trend was very small for all markers (less than 2.5%). Less than 1% of the between-person variance was accounted for by seasonality in the cross-sectional analysis for all markers (n = 2780). There was a small but statistically significant summertime increase in OC and PINP in the healthy postmenopausal population after exclusions based on disease or medication use (remaining n = 1226, amplitudes 5.6% and 5.4%, respectively, p < 0.001).

CONCLUSIONS

We have been unable to confirm findings of a marked wintertime increase in bone formation and resorption within the general population. The absence of marked seasonality was irrespective of age, menopausal status, reported supplemental Vitamin D intake, age or geographical location. The small but statistically significant summertime increase in bone formation in this and other studies is unlikely to confound clinical interpretation of these measurements.

Release of lead from bone in pregnancy and lactation

Concentrations and isotope ratios of lead in blood, urine, 24-h duplicate diets, and hand wipes were measured for 12 women from the second trimester of pregnancy until at least 8 months after delivery. Six bottle fed and six breast fed their infants. One bottle feeder fell pregnant for a second time, as did a breast feeder, and each was followed semicontinuously for totals of 44 and 54 months, respectively. Bone resorption rather than dietary absorption controls changes in blood lead, but in pregnancy the resorption of trabecular and cortical bone are decoupled. In early pregnancy, only trabecular bone (presumably of low lead content) is resorbed, causing blood leads to fall more than expected from hemodilution alone. In late pregnancy, the sites of resorption move to cortical bone of higher lead content and blood leads rise. In bottle feeders, the cortical bone contribution ceases immediately after delivery, but any tendency for blood leads to fall may be compensated by the effect of hemoconcentration produced by the postpartum loss of plasma volume. In lactation, the whole skeleton undergoes resorption and the blood leads of nursing mothers continue to rise, reaching a maximum 6-8 months after delivery. Blood leads fall from pregnancy to pregnancy, implying that the greatest risk of lead toxicity lies with first pregnancies.

Influence of smoking and oral contraceptives on bone mineral density and bone remodeling in young women: a 2-year study

The objective of the study was to explore the influence of menstrual irregularities, oral contraceptives and smoking on bone mineral density (BMD) development and bone turnover with time. Healthy young women (n = 118) were divided into four categories: (a) women neither smoking nor using oral contraceptives; (b) women who were smokers; (c) women using oral contraceptives; (d) women who were smoking and using oral contraceptives. They responded to a validated questionnaire with 34 questions concerning lifestyle and the Sense of Coherence scale (SOC). BMD was measured by dual energy x-ray absorptiometry (DEXA). Deoxypyridinoline (DPD) was measured in urine. Data were analyzed by multiple linear regression analysis. Among smokers, BMD level decreased during a 2-year period and smoking was associated with a larger negative change in BMD. Use of oral contraceptives moderated the negative impact of smoking. Women using oral contraceptives at baseline and with regular bleeding induced by contraceptive pills had a significantly higher BMD at baseline and at follow-up. They also had lower SOC than women who had natural regular bleedings. Use of oral contraceptives in combination with smoking was linked to high alcohol consumption and higher frequency of self-reported body weight reduction, which reduced the negative BMD change in this category. DPD level and difference were strongly associated with estrogen influence. It is concluded that smokers without OCs had a negative BMD development and BMD in young women with irregular menstruations seems to be improved by OC.

Biochemical markers of bone turnover and development of heterotopic ossification after total hip arthroplasty

We studied biochemical markers of bone turnover markers in 20 men and women over 26 weeks after total hip arthroplasty (THA) in order to characterize the changes in bone metabolism associated with developing heterotopic ossification (HO). Transient increases in biochemical markers of both osteoclast and osteoblast activity occurred after surgery. Subjects developing HO (n=9) had greater rises in the osteoclast marker C-telopeptide of type-I collagen (CTX-I; ANOVA P=0.004), and the osteoblast markers N-terminal propeptide of type-I procollagen (PINP; ANOVA P=0.01) and osteocalcin (OC; ANOVA P=0.02) than those who did not develop HO. A rise of >42% in CTX-I at one week after surgery had a sensitivity of 89% and a specificity of 82% for predicting HO development at week 26 (P<0.05). Rises of >57% in PINP and >13% in OC at week 6 had sensitivities of 89% and 56%, and specificities of 82% and 91%, respectively for development of HO. Transient increases in osteoblast and osteoclast activity occur after THA. These changes are greater in patients developing HO than in those who do not develop HO. The potential applications of these markers are as a non-invasive, radiation-free tool for investigating the pathogenesis of HO, and as an early surrogate outcome marker for HO development in clinical trials of novel prophylaxis regimes for its prevention.

Is the predictive power of previous fractures for new spine and non-spine fractures associated with biochemical evidence of altered bone remodelling? The EPOS study. European Prospective Osteoporosis Study

BACKGROUND

In the European Prospective Osteoporosis Study (EPOS), a past spine fracture increased risk of an incident fracture 3.6 - 12-fold even after adjusting for BMD. We examined the possibility that biochemical marker levels were associated with this unexplained BMD-independent element of fracture risk.

METHODS

Each of 182 cases in EPOS of spine or non-spine fracture that occurred in 3.8 years of follow-up was matched by age, sex and study centre with two randomly assigned never-fractured controls and one case of past fracture. Analytes measured blind were: osteocalcin, bone-specific alkaline phosphatase, total alkaline phosphatase, serum creatinine, calcium, phosphate and albumin, together with the collagen cross-links degradation products serum CTS and urine CTX. Most subjects also had bone density measured by DXA.

RESULTS

Cases who had recent fractures did not differ in marker levels from cases who had their last fracture more than 3 years previously. No statistically significant effect of recent fracture was found for any marker except osteocalcin, which was 17.6% lower in recent peripheral cases compared to unfractured controls (p<0.05) and this was independent of BMD.

CONCLUSION

Past fracture as a risk indicator for future fracture is not strongly mediated through increased bone turnover.

Effect of feeding on bone turnover markers and its impact on biological variability of measurements

Bone turnover markers are subject to day-to-day and within-day variability, which may influence clinical interpretation. We examined the effect of fasting vs. feeding on the concentration and between-day variability of several markers. Twenty healthy premenopausal women were studied on 10 consecutive weekdays. Subjects were studied either in the fasting (no breakfast) or fed (breakfast at 08:00 h) state on alternate days, and were randomized to begin either fasting or fed. Two hour urine collections were obtained each day between 08:00 h and 10:00 h, and blood samples were collected daily at 09:00 h. The N-telopeptide cross-link of type I collagen in urine (uNTX) and serum (sNTX), the C-telopeptide in urine (uCTX) and serum (sbetaCTX), and immunoreactive free deoxypyridinoline (uifDPD) in urine were measured as resorption markers. Procollagen type I N-terminal propeptide (PINP), osteocalcin (OC), and bone alkaline phosphatase (bone ALP) were measured as formation markers. All bone formation and resorption markers were significantly lower in the fed state with the exception of bone ALP. The magnitude of the decrease ranged from 3.8 +/- 0.9% for PINP (p < 0.0001) to 17.8 +/- 2.6% (p < 0.0001) for sbetaCTX. Measurement variability was partitioned into analytical variability based on replicate assays (CV(a)) and within-subject variability (CV(i)). The CV(i) was greater (p < 0.05) for some markers in the fasting state (uifDPD, uNTX, and sNTX) but greater in the fed state for other markers (OC and sbetaCTX). In conclusion, the clinical impact of feeding vs. fasting is small with the exception of sbetaCTX; however, in clinical practice, collection of samples in the fasting state may be necessary to minimize the unpredictable effects of feeding. The mechanism of the acute effect of feeding on bone turnover remains uncertain.

Osteoporosis in childhood: bone density of children in health and disease

Bone mineral density in later life largely depends on the peak bone mass achieved in adolescence or young adulthood. A reduced bone density is associated with increased fracture risk in adults as well as in children. Pediatricians should therefore play an important role in the early recognition and treatment of childhood osteoporosis. Juvenile idiopathic osteoporosis and osteogenesis imperfecta are examples of primary osteoporosis in childhood. However, osteoporosis is more frequently a complication of a chronic disease or its treatment. This paper provides an overview of bone and bone metabolism in healthy children and the use of diagnostic tools, such as biochemical markers of bone turnover and several bone densitometry techniques. Furthermore, a number of diseases associated with osteoporosis in childhood and possible treatment strategies are discussed.

Role of biochemical markers in the management of osteoporosis

Several serum and urine biochemical markers of bone resorption and formation have been developed. Biochemical bone markers have been used as intermediate end-points in all major studies of anti-osteoporotic therapies. Bone resorption markers, in particular, may add an independent, predictive value to the assessment of bone loss and fracture risk. There are also potential advantages in monitoring anti-osteoporotic treatment in the short-term in addition to bone densitometry, to rapidly identify non-responders to therapy, or non-compliance. Despite these recent advances, until now bone markers have simply been very useful research tools, with their clinical utility being limited by intra-individual and diurnal variability. However, the probability of the true bone mineral density response to hormone replacement therapy for the individual patient may be predicted using algorithms based on a spectrum of cut-off bone marker levels with varying false positive and negative rates. Thus, the transition of biochemical bone markers into everyday clinical practice may be rapidly approaching.