Low vitamin D status: definition, prevalence, consequences, and correction

Low vitamin D status is extremely common worldwide due to low dietary intake and low skin production. Suboptimal vitamin D status contributes to many conditions, including osteomalacia/rickets, osteoporosis, falls, and fractures. It is possible or even likely that low vitamin D status increases risk for a multitude of other conditions. Although consensus does not exist, it appears that circulating 25(OH)D concentrations greater than 30 to 32 ng/mL are needed for optimal health. To achieve this, daily intakes of at least 1000 IU of D3 daily are required, and it is probable that substantially higher amounts are required to achieve such values on a population basis. It seems premature to recommend widespread screening for 25(OH)D measurement. Targeted measurement in those at increased risk for vitamin D deficiency and those most likely to have a prompt positive response to supplementation is appropriate. Widespread optimization of vitamin D status likely will lead to prevention of many diseases with attendant reduction of morbidity, mortality, and expense.

BMD measurement and precision: a comparison of GE Lunar Prodigy and iDXA densitometers

This study assessed bone mineral density (BMD) comparability and precision using Lunar Prodigy and iDXA densitometers (GE Healthcare, Madison, WI) in adults. Additionally, the utility of supine forearm measurement with iDXA was investigated. Lumbar spine and bilateral proximal femur measurements were obtained in routine clinical manner in 345 volunteers, 202 women and 143 men of mean age 52.5 (range: 20.1-91.6)yr. Seated and supine distal forearm scans were obtained in a subset (n=50). Lumbar spine and proximal femur precision assessments were performed on each instrument following International Society for Clinical Densitometry recommendations in 30 postmenopausal women. BMD at the L1-L4 spine, total proximal femur, and femoral neck was very highly correlated (r(2)≥0.98) between densitometers, as was the one-third radius site (r(2)=0.96). Bland-Altman analyses demonstrated no clinically significant bias at all evaluated sites. BMD precision was similar between instruments at the L1-L4 spine, mean total proximal femur, and femoral neck. Finally, one-third radius BMD measurements in the supine vs seated position on the iDXA were highly correlated (r(2)=0.96). In conclusion, there is excellent BMD correlation between iDXA and Prodigy densitometers. Similarly, BMD precision is comparable with these two instruments.

Leptin excites enteric neurons of guinea-pig submucous and myenteric plexus

BACKGROUND

Leptin, one of the most prominent mediators released from adipocytes, influences neuronal activity in the central nervous system. The enteric nervous system (ENS) expresses leptin receptors but consequence of activation of these receptors on enteric neuron activity has not been systematically studied. An adipocyte-ENS axis is suggested by close apposition between enteric nerves and adipocytes. The aim of this study was to investigate the effects of leptin on guinea-pig submucous and myenteric neurons.

METHODS

Using voltage sensitive dye imaging, we recorded neural responses to application of leptin (0.0625 nmol L(-1)) in myenteric and submucous neurons, nicotine (10 μmol L(-1)) served as a reference for neuronal excitation. Mucosal ion secretion and muscle activity were measured in vitro with Ussing and organ bath techniques, respectively.

KEY RESULTS

Leptin induced spike discharge in 13.6% of submucous neurons and in 8.2% of myenteric neurons (1.1 ± 0.9 and 1.2 ± 1.0 Hz, respectively). Although there was an overlap of nicotine and leptin responses, 38.5% of submucous and 25% of myenteric neurons activated by leptin did not respond to nicotine. Leptin did not inhibit ongoing spike discharge or fast excitatory postsynaptic potentials. Leptin (0.0625 nmol L(-1)) did not affect mucosal secretion or muscle activity suggesting a subtle modulatory action of leptin at the level of the ENS.

CONCLUSIONS & INFERENCES

Leptin activates submucous and myenteric neurons indicating relevance for adipocyte-ENS signaling. These results set the basis for further studies to reveal the functional correlate of the neural action of leptin in the ENS.

Evaluation of ergocalciferol or cholecalciferol dosing, 1,600 IU daily or 50,000 IU monthly in older adults

CONTEXT

Whether ergocalciferol (D(2)) and cholecalciferol (D(3)) are equally effective to increase and maintain serum 25-hydroxyvitamin D [25(OH)D] concentration is controversial.

OBJECTIVE

The aim of the study was to evaluate the effect of daily and once monthly dosing of D(2) or D(3) on circulating 25(OH)D and serum and urinary calcium.

DESIGN, SETTING AND PARTICIPANTS

In a university clinical research setting, 64 community dwelling adults age 65+ were randomly assigned to receive daily (1,600 IU) or once-monthly (50,000 IU) D(2) or D(3) for 1 yr.

MAIN OUTCOME MEASURES

Serum 25(OH)D, serum calcium, and 24-h urinary calcium were measured at months 0, 1, 2, 3, 6, 9, and 12. Serum PTH, bone-specific alkaline phosphatase, and N-telopeptide were measured at months 0, 3, 6, and 12.

RESULTS

Serum 25(OH)D was less than 30 ng/ml in 40% of subjects at baseline; after 12 months of vitamin D dosing, levels in 19% of subjects (n = 12, seven receiving daily doses and five monthly doses) remained low, despite compliance of more than 91%. D(2) dosing increased 25(OH)D(2) but produced a decline (P < 0.0001) in 25(OH)D(3). Substantial between-individual variation in 25(OH)D response was observed for both D(2) and D(3). The highest 25(OH)D observed was 72.5 ng/ml. Vitamin D administration did not alter serum calcium, PTH, bone-specific alkaline phosphatase, N-telopeptide, or 24-h urine calcium.

CONCLUSIONS

Overall, D(3) is slightly, but significantly, more effective than D(2) to increase serum 25(OH)D. One year of D(2) or D(3) dosing (1,600 IU daily or 50,000 IU monthly) does not produce toxicity, and 25(OH)D levels of less than 30 ng/ml persist in approximately 20% of individuals. Substantial between-individual response to administered vitamin D(2) or D(3) is observed.

Signaling mechanisms involved in the intestinal pro-secretory actions of hydrogen sulfide

BACKGROUND

H(2) S actions in the gut involve neural activation. This study aimed to reveal the signaling mechanisms responsible for the pro-secretory effect of H(2) S by using TRPV1 and unselective TRP blockers and inhibitors of other signaling cascades hitherto described to be targeted by H(2) S elsewhere.

METHODS

Ussing chamber voltage clamp technique was used to study actions of the H(2) S donor NaHS on secretion in guinea-pig and human colon. NaHS effects on guinea-pig primary afferents were also evaluated.

KEY RESULTS

NaHS evoked secretion was significantly reduced in guinea-pig and human tissue by the selective TRPV1 blockers capsazepine, AMG9801, SB705498, BCTC; LY294002 (Phosphatidylinositol-3 kinase (PI3K) inhibitor), SKF96365 (store operated calcium channel blocker), 2-APB (inositol triphosphate blocker), and atropine but not by HC030031 (TRPA1 blocker) or L- and T-type calcium channel antagonists. Actions of TRPV1 antagonists suggested non-competitive inhibition at multiple sites. In guinea-pig colon, Gd(3+) and La(3+) (unselective TRP blockers) had no effects while ruthenium red reduced NaHS effects; in human colon Gd(3+) attenuated NaHS response. NaHS response was inhibited by neurokinin-1 and -3 receptor blockers in guinea-pig and neurokinin-1 and -2 receptor blockade in human tissue. There was cross-desensitization between NaHS and capsaicin responses. NaHS induced capsazepine and LY294002 sensitive afferent discharge.

CONCLUSIONS & INFERENCES

H(2) S evokes mucosal secretion by targeting TRPV1 expressing afferent nerves which activate cholinergic secretomotor neurons via release of substance P acting in a species dependent manner on neurokinin-1, -2 or -3 receptors. Besides TRPV1 signaling H(2) S may target intracellular calcium dependent pathways and PI3K.

Jumping mechanography: a potential tool for sarcopenia evaluation in older individuals

Muscular function declines with advancing age and is associated with increased risk for falls and fragility fractures. No single methodology ideally quantitatively evaluates this decline. Jumping mechanography (JM) may prove useful to quantitatively measure muscular function in older adults. This study begins to evaluate the safety of JM and the relationship of jump power and lean mass in older adults. Eighty adults, 40 aged 20-30 yr and 40 aged 60 yr or older, distributed equally by gender, participated. They performed countermovement jumps to assess jump power and height. Self-reported pain before and after jumping and need for assistance was recorded. In the older group, dual-energy X-ray absorptiometry was used to measure bone mineral density, to estimate lean body mass, and to determine vertebral fracture status. Jumping was well tolerated without injury or increased pain. No new vertebral fractures occurred with jumping in the older group. Young individuals had greater jump power and height compared with the older group. Older age was negatively correlated, whereas lean mass positively correlated with jump power and height. JM appears to be a safe and potentially useful method to assess muscular function in older adults.

Low vitamin D status: definition, prevalence, consequences, and correction

Vitamin D is obtained from cutaneous production when 7-dehydrocholesterol is converted to vitamin D(3) (cholecalciferol) by ultraviolet B radiation or by oral intake of vitamin D(2) (ergocalciferol) and D(3). An individual's vitamin D status is best evaluated by measuring the circulating 25-hydroxyvitamin D (25(OH)D) concentration. Although controversy surrounds the definition of low vitamin D status, there is increasing agreement that the optimal circulating 25(OH)D level should be approximately 30 to 32 ng/mL or above. Using this definition, it has been estimated that approximately three-quarters of all adults in the United States have low levels. Low vitamin D status classically has skeletal consequences such as osteomalacia/rickets. More recently, associations between low vitamin D status and increased risk for various nonskeletal morbidities have been recognized; whether all of these associations are causally related to low vitamin D status remains to be determined. To achieve optimal vitamin D status, daily intakes of at least 1000 IU or more of vitamin D are required. The risk of toxicity with "high" amounts of vitamin D intake is low. Substantial between-individual variability exists in response to the same administered vitamin D dose. When to monitor 25(OH)D levels has received little attention. Supplementation with vitamin D(3) may be preferable to vitamin D(2).

Vertebral fracture assessment: impact of instrument and reader

PURPOSE

Many osteoporotic vertebral fractures are not clinically recognized but increase fracture risk. We hypothesized that a newer generation densitometer increases the number of evaluable vertebrae and vertebral fractures detected. We also explored the impact of reader experience on vertebral fracture assessment (VFA) interpretation.

METHODS

VFA images obtained using Prodigy and iDXA densitometers in 103 older adults were evaluated for vertebral visualization and fracture presence in the T4-L5 region. A "true" read for each densitometer was achieved by consensus. If readers disagreed, the evaluation of a third expert physician was taken as true. Main outcomes were evaluable vertebrae, vertebral fractures, and intrareader/interreader reproducibility.

RESULTS

Using the "true" reads, 92% of vertebrae were visualized on iDXA and 76% on Prodigy. Numerically, more fractures were identified with iDXA; the "true" reads found 43 fractures on iDXA and 21 on Prodigy. The experienced reader had better intrareader and interreader reproducibility than the inexperienced reader when compared with the "true" read.

CONCLUSIONS

Using the newer iDXA densitometer for VFA analysis improves vertebral body visualization and fracture detection. Training and experience enhance result reproducibility.

Slight abduction/adduction deviations in femur positioning for dual-energy X-ray absorptiometry are inconsequential

Straight femur alignment during dual-energy X-ray absorptiometry (DXA) acquisition is assumed to help ensure accurate bone mineral density (BMD) measurement. Use of bilateral femur positioners may not result in straight femur alignment. To assess the effect of a bilateral femur positioner on DXA results, we compared a standard fixed-width bilateral femur positioner with an adjustable-width positioner that allowed for straight femur alignment. BMD values obtained from the adjustable-width bilateral femur positioner were highly correlated (R(2)=0.98-0.99) with those obtained using a fixed-width positioner. The mean bias in BMD between the fixed- and adjustable-width positioner was low (-0.001 to +0.006g/cm(2)) at all proximal femur regions of interest. In this study, the use of a fixed-width bilateral femur positioner and associated deviations in femur alignment have little consequence on BMD measurement.

The multi-herbal drug STW 5 (Iberogast) has prosecretory action in the human intestine

There is growing evidence that STW 5 (Iberogast), fixed combination of hydroethanolic herbal extracts), besides being effective in functional dyspepsia, also improves symptoms in irritable bowel syndrome (IBS). Clinical data indicate that modulation of mucosal secretion is a promising approach to treat intestinal disorders associated with IBS. We therefore explored the effect of STW 5 on secretion in the human intestine and the mechanisms by which it acts. The Ussing chamber technique was used to measure mucosal secretion in human intestinal mucosa/submucosa preparations and in human epithelial cell line T84. In addition, we recorded STW 5 effects on human enteric neurons with voltage sensitive dye imaging. In human tissue and T84 cells STW 5 induced a dose-dependent increase in ion secretion that was significantly reduced by the Na-K-Cl cotransporter blocker bumetanide, the adenylate cyclase inhibitor MDL-12 330, the non-specific and selective cystic fibrosis transmembrane conductance regulator (CFTR) inhibitors glibenclamide and CFTR(inh)-172, respectively, and the blocker of calcium dependent Cl(-) channels (ClCa) SITS (4-acetamido-4-isothiocyanatostilbene-2,2-disulphonic acid). It was unaffected by amiloride, a blocker of epithelial Na(+) channels. In human tissue, the nerve blocker tetrodotoxin significantly suppressed the STW 5 response. STW 5 evoked an increased spike discharge in 51% of human submucous neurons. Results suggest that STW 5 is a secretogogue in the human intestine by direct epithelial actions and through activation of enteric neurons. The prosecretory effect is due to increased epithelial Cl(-) fluxes via CFTR and Ca-dependent ClCa channels. STW 5 may be a novel option to treat secretory disorders associated with IBS and constipation.

25-hydroxyvitamin D measurement, 2009: a review for clinicians

As clinicians are more widely appreciating the endemic nature of low vitamin D status, measurement of serum 25-hydroxyvitamin D (25(OH)D), the accepted measure of vitamin D status, has increased. Challenges to 25(OH)D measurement include the presence of 2 forms of vitamin D-ergocalciferol and cholecalciferol (vitamin D(2) and vitamin D(3), respectively)- and the hydrophobic nature of vitamin D. The current state of 25(OH)D measurement is reviewed; modest differences between methodologies persist and confound the application of a single cut point (e.g., 30 ng/mL/75 nmol/L) for the diagnosis of low vitamin D status. The absence of standard calibrators contributes to between-laboratory differences in 25(OH)D measurement. Until there is improved assay standardization and subsequent evidence-based consensus, it seems premature to recommend widespread screening 25(OH)D measurement. Selectively obtaining 25(OH)D measurement in individuals at clinical risk for vitamin D deficiency and/or those most likely to promptly experience benefits from supplementation seems appropriate.

What should DXA reports contain? Preferences of ordering health care providers

It has previously been reported that clinicians prefer detailed dual-energy X-ray absorptiometry (DXA) reports. However, there are limited recent data to support this contention. Given the emphasis on bone mass measurement and osteoporosis treatment that occurred over the past decade, we hypothesized that clinicians would no longer desire detailed DXA reports. As such, we surveyed 234 university health care providers who had ordered one or more DXA scans from October 2005 through February 2006. All providers were requested to complete an anonymous survey expressing their preferences regarding potential elements of a central DXA report using a 1-5 scale. Of the 234 surveys sent, 116 (50%) were returned. Over 90% felt that DXA reports should include a statement regarding the study's technical quality and limitations, the T-score and definition of significant change. Similarly, over 80% felt that a statement about fracture risk and the BMD least significant change to be essential or helpful. Although a majority of clinicians requested recommendations for non-BMD testing, pharmacologic/nonpharmacologic interventions and specific recommendations for evaluation of secondary osteoporosis, a substantial minority (approximately 20%) found such recommendations either not required or definitely unnecessary. That this survey was conducted among university clinicians is a limitation, which may impact generalizability. In conclusion, clinicians responding to this survey continue to prefer detailed DXA reports with over 60% desiring inclusion of all the components recommended for DXA reports by the International Society for Clinical Densitometry. Despite the finding that a majority of providers continue to request such "consultative" reports, DXA interpreters should be cautioned that this approach requires fairly extensive and accurate clinical information and that not all clinicians desire recommendations for additional evaluation and treatment.

Rapid correction of low vitamin D status in nursing home residents

This prospective study finds that ergocalciferol 50,000 IU three times weekly for four weeks effectively and safely corrects vitamin D inadequacy in nursing home residents.

INTRODUCTION

Low vitamin D status is common among nursing home residents and contributes to bone loss, falls and fractures. The objective of this study was to evaluate the efficacy and safety of short course, high dose, oral vitamin D(2) (ergocalciferol) treatment.

METHODS

This prospective study included 63 nursing home residents. The 25 with low vitamin D status (serum 25(OH)D < or = 25 ng/ml) received oral ergocalciferol 50,000 IU three times weekly for four weeks; the others received no change to their routine care. Serum total 25(OH)D, 25(OH)D(2), 25(OH)D(3), calcium, parathyroid hormone (PTH), bone turnover markers and neuro-cognitive assessments were obtained at baseline and four weeks.

RESULTS

Mean total 25(OH)D concentration increased (p < 0.0001) from 17.3 to 63.8 ng/ml in the treated group and remained unchanged in the comparison group. Serum 25(OH)D(3) remained stable in the comparison group, but declined (p < 0.0001) with D(2) treatment from 15.4 to 9.1 ng/ml. Serum PTH trended down in the treatment group (p = 0.06). No treatment-induced improvement in ambulation, cognition or behavior was observed. No hypercalcemia or other adverse effects were observed with ergocalciferol treatment.

CONCLUSION

Four weeks of oral vitamin D(2) supplementation effectively and safely normalizes serum 25(OH)D in nursing home residents.

Evaluation and correction of low vitamin D status

Low vitamin D status, which is endemic due to inadequate oral intake combined with sun avoidance, contributes to musculoskeletal and other pathologies. Although controversial, it is increasingly recommended that serum 25-hydroxyvitamin D (25D) concentrations less than 30 ng/mL be considered suboptimal. Clinicians should appreciate that 25(OH)D measurements, like all quantitative laboratory tests, are subject to assay and biologic variability. Additionally, international standardized calibrators do not exist for 25(OH)D measurement. As such, a single 25(OH)D value of "30 ng/mL" may have substantial variability surrounding it, thereby making 25(OH)D levels of approximately 35 to 40 ng/mL a reasonable therapeutic goal to assure vitamin D adequacy. Achieving such levels often requires vitamin D supplementation. Vitamin D3 (cholecalciferol) or D2 (ergocalciferol) may be used; whether vitamin D3 is more potent than vitamin D2 in maintaining 25(OH)D is controversial.

Correlation among 25-hydroxy-vitamin D assays

CONTEXT

Measurement of circulating 25-hydroxy-vitamin D [25(OH)D]) is the accepted clinical indicator of vitamin D status. However, between-laboratory differences in measurement of this analyte exist, which may confound clinical care.

OBJECTIVES

We investigated the current agreement of 25(OH)D measurement in clinical laboratories and explored the possibility that simple calibration would improve between-laboratory agreement.

DESIGN AND PARTICIPANTS

Serum obtained from healthy volunteers (age 20-60 yr) and one "calibrator," selected to have a 25(OH)D value near 30 ng/ml, were sent for 25(OH)D measurement in four clinical laboratories (laboratories A-D) using HPLC, liquid chromatography tandem mass spectroscopy, and RIA methodologies.

MAIN OUTCOME MEASURES

Serum 25(OH)D. Based upon self-report, the laboratory with the lowest interassay percent coefficient of variation was assigned as the reference to which the others were compared using linear regression and Bland-Altman analyses (Analyse-it; Analyse-it Software, Ltd., Leeds, UK).

RESULTS

Good correlation was observed for 25(OH)D measurement between laboratory A and laboratories B-D (R(2) = 0.99, 0.81, and 0.95, respectively). Modest between-laboratory variation was noted; the mean bias ranged from 2.9-5.2 ng/ml. Consistent with a systematic offset, each value in laboratory B was higher than in laboratory A, and 89% of values from laboratories B-D were higher than laboratory A. The use of a single calibrator and correction factor reduced mean between-laboratory bias for laboratories B and D.

CONCLUSIONS

Measurement of 25(OH)D by clinical laboratories yields similar results. The use of even a single calibrator will improve, but not resolve, between-laboratory variability. Based upon these data, in combination with reported within-individual variability, we recommend that clinicians aim for values greater than 30 ng/ml in their patients.

Low vitamin D status: time to recognize and correct a Wisconsin epidemic

As a result of low dietary intake and sun avoidance, low vitamin D status is endemic in Wisconsin. In a convenience sample of postmenopausal Wisconsin residents, 59% had suboptimal D status. Only recently, the medical community has begun to appreciate that low vitamin D status underlies multiple deleterious health consequences including skeletal fragility, muscle weakness, and a potential multitude of non-skeletal morbidities. At present, a routine recommendation indicates that at least 1000 IU of vitamin D3 (cholecalciferol) daily is indicated, although the true requirement may be greater. This review details vitamin D physiology and the prevalence of low vitamin D status in Wisconsin and elsewhere, and provides approaches to optimizing vitamin D status.

An evaluation of densitometric vertebral fracture assessment in men

The utility of, and potential indications for, densitometric vertebral fracture assessment were evaluated in 1,168 men. A bimodal fracture distribution was observed, identifying fractures in 17% of men with no fracture history. Osteopenia or height loss of > or = 2.5'' may be indications for VFA in men.

INTRODUCTION

Densitometric vertebral fracture assessment (VFA) is an excellent means to detect unappreciated vertebral fractures in women. However, little evaluation of VFA in men has been performed. This study evaluated VFA utility and explored potential VFA indications in men.

METHODS

The study cohort consists of a population of 1,168 men (mean age, weight and BMI of 69.1 years, 188.8 pounds and 28.1 kg/m(2), respectively) referred for clinically indicated bone mineral density (BMD) measurement at the Wm. S. Middleton VAMC. Lateral VFA images and scans of the lumbar spine, proximal femur and non-dominant radius, were obtained by two technologists using a GE Healthcare Lunar Prodigy densitometer. Vertebral fractures were defined using the Genant visual semi-quantitative approach.

RESULTS

Seventy-eight percent of vertebrae from T4-L5 and 93% from T8-L5 were adequately visualized on VFA. Vertebral fractures were detected in 32% (374/1,168) of these men. A bimodal distribution was observed with fractures being most common in the mid-thoracic spine and at the thoraco-lumbar junction. As would be expected, the prevalence of VFA-detected fractures increased with age and as BMD declined. Fracture prevalence did not increase until a historical height loss of > or = 6.4 cm (2.5 inches) was reported. VFA-identified fractures were present in 17% of men who had no history of fracture. Furthermore, in men with densitometric osteopenia, no historical fracture and absence of glucocorticoid use (n = 158), vertebral fractures were detected in 18%.

CONCLUSION

VFA allows evaluation of the majority of vertebral bodies in men and identifies a substantial number of individuals with previously unappreciated fracture. Additionally, a more stringent height loss requirement, perhaps 2.5 inches or more, or densitometric osteopenia (low bone mineral density by DXA), may be appropriate as indications for performance of VFA in men.

Effect of female database use for T-score derivation in men

Whether to use male or female databases to obtain T-scores in men remains controversial. This study evaluated the impact of deriving male T-scores using female databases in 350 men aged 22.8-93.5 (mean 67.5+/-12.2) yr who were referred for clinically indicated dual-energy X-ray absorptiometry exams. Spine, femur, and nondominant radius scans were obtained in routine clinical manner using a GE Healthcare Lunar Prodigy densitometer. Analyses were performed using software version 9.30. Initially, the GE Healthcare Lunar male normative database was used to calculate T-scores. Subsequently, scans were reanalyzed using female databases; GE for the spine and radius, and NHANES III for the femur. Using the manufacturer's male database, T-scores (mean [range]) of the L1-4 spine, femur neck, total femur, and .3 radius were 0.0 [-4.6 to +8.5], -1.6 [-4.3 to +2.3], -1.1 [-4.0 to +3.3], and -0.7 [-5.3 to +2.9], respectively. On reanalysis with female databases, T-scores "improved" (p<0.0001) with a positive bias of 0.34, 0.33, 0.58, and 1.20, respectively at the above 4 sites. Using female databases, the proportion of men classified as having normal bone mass increased from 22% to 33% and those identified as osteoporotic decreased from 29% to 17%. If pharmacologic treatment were prescribed at a T-score <-2.0, use of the female databases would reduce those treated for low bone mass from 46% to 32%. In conclusion, using female databases to derive male T-scores results in "improvement" of diagnostic classification for a substantial number of men with fewer being classified as having low bone mass.

Low vitamin D status despite abundant sun exposure

CONTEXT

Lack of sun exposure is widely accepted as the primary cause of epidemic low vitamin D status worldwide. However, some individuals with seemingly adequate UV exposure have been reported to have low serum 25-hydroxyvitamin D [25(OH)D] concentration, results that might have been confounded by imprecision of the assays used.

OBJECTIVE

The aim was to document the 25(OH)D status of healthy individuals with habitually high sun exposure.

SETTING

This study was conducted in a convenience sample of adults in Honolulu, Hawaii (latitude 21 degrees ).

PARTICIPANTS

The study population consisted of 93 adults (30 women and 63 men) with a mean (sem) age and body mass index of 24.0 yr (0.7) and 23.6 kg/m(2) (0.4), respectively. Their self-reported sun exposure was 28.9 (1.5) h/wk, yielding a calculated sun exposure index of 11.1 (0.7).

MAIN OUTCOME MEASURES

Serum 25(OH)D concentration was measured using a precise HPLC assay. Low vitamin D status was defined as a circulating 25(OH)D concentration less than 30 ng/ml.

RESULTS

Mean serum 25(OH)D concentration was 31.6 ng/ml. Using a cutpoint of 30 ng/ml, 51% of this population had low vitamin D status. The highest 25(OH)D concentration was 62 ng/ml.

CONCLUSIONS

These data suggest that variable responsiveness to UVB radiation is evident among individuals, causing some to have low vitamin D status despite abundant sun exposure. In addition, because the maximal 25(OH)D concentration produced by natural UV exposure appears to be approximately 60 ng/ml, it seems prudent to use this value as an upper limit when prescribing vitamin D supplementation.

Vitamin K deficiency from long-term warfarin anticoagulation does not alter skeletal status in male rhesus monkeys

Vitamin K (K) inadequacy may cause bone loss. Thus, K deficiency induced by anticoagulants (e.g., warfarin) may be an osteoporosis risk factor. The skeletal impact of long-term warfarin anticoagulation was evaluated in male monkeys. No effect on BMD or bone markers of skeletal turnover was observed. This study suggests that warfarin-induced K deficiency does not have skeletal effects.

INTRODUCTION

The skeletal role of vitamin K (K) remains unclear. It is reasonable that a potential role of vitamin K in bone health could be elucidated by study of patients receiving oral anticoagulants that act to produce vitamin K deficiency. However, some, but not all, reports find K deficiency induced by warfarin (W) anticoagulation to be associated with low bone mass. Additionally, epidemiologic studies have found W use to be associated with either increased or no change in fracture risk. Such divergent results may imply that human studies are compromised by the physical illnesses for which W was prescribed.

MATERIALS AND METHODS

To remove this potential confounder, we prospectively assessed skeletal status during long-term W anticoagulation of healthy nonhuman primates. Twenty adult (age, 7.4-17.9 yr, mean, 11.7 yr) male rhesus monkeys (Macaca mulatta) were randomized to daily W treatment or control groups. Bone mass of the total body, lumbar spine, and distal and central radius was determined by DXA at baseline and after 3, 6, 9, 12, 18, 24, and 30 mo of W treatment. Serum chemistries, urinary calcium excretion, bone-specific alkaline phosphatase, and total and percent unbound osteocalcin were measured at the same time-points. Prothrombin time and international normalized ratio (INR) were monitored monthly. Serum 25-hydroxyvitamin D was measured at the time of study conclusion.

RESULTS

W treatment produced skeletal K deficiency documented by elevation of circulating undercarboxylated osteocalcin (8.3% W versus 0.4% control, p<0.0001) but did not alter serum markers of skeletal turnover, urinary calcium excretion, or BMD.

CONCLUSIONS

In male rhesus monkeys, long-term W anticoagulation does not alter serum markers of bone turnover or BMD. Long-term W therapy does not have adverse skeletal consequences in primates with high intakes of calcium and vitamin D.