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The Journal of Clinical Endocrinology & Metabolism Vol. 89, No. 4 1572-1576
Copyright © 2004 by The Endocrine Society

Serum Parathyroid Hormone Predicts Time to Fall Independent of Vitamin D Status in a Frail Elderly Population

P. N. Sambrook, J. S. Chen, L. M. March, I. D. Cameron, R. G. Cumming, S. R. Lord, J. Zochling, Y. Y. Sitoh, T. C. Lau, J. Schwarz and M. J. Seibel

Institute of Bone and Joint Research, Department of Public Health, ANZAC Research Institute, University of Sydney, Prince of Wales Medical Research Institute, Sydney, New South Wales 2065, Australia

Address all correspondence and requests for reprints to: Prof. Philip Sambrook, Institute of Bone and Joint Research, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia. E-mail: sambrook{at}med.usyd.edu.au.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Very frail older people constitute an increasing proportion of ageing populations and often have vitamin D deficiency. Falls are frequent in this population and have usually been associated with vitamin D deficiency. In this prospective study we measured serum 25-hydroxyvitamin D (25OHD), serum PTH, and falls in 637 ambulatory subjects living in institutional aged care facilities (intermediate-care hostels or nursing homes). The study sample comprised 121 men (mean age, 82.1 yr) and 516 women (mean age, 86.7 yr). Two hundred and seventy-four subjects fell one or more times over a mean duration of follow-up of 10.2 months. Vitamin D deficiency, defined as a serum 25OHD level below 39 nmol/liter was present in 73.6%. Baseline serum 25OHD and PTH were significantly associated with falls in univariate analyses. In multivariate analyses that also corrected for balance and health status, PTH remained a significant predictor of falls independent of 25OHD. Serum PTH is a predictor of time to first fall in the frail elderly independent of vitamin D status and measures of general health.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
FALLS ARE A major health care concern in the frail elderly living in residential facilities (1, 2, 3, 4, 5, 6, 7). Nursing home and intermediate-care (hostel) residents have increased levels of chronic illness (6), medication use (3, 5, 7), cognitive disorders (7), as well as neuromuscular impairments (1, 5, 6, 7). Vitamin D deficiency is also common in this population and is thought to be a contributing factor to falls risk via effects on neuromuscular function (8, 9, 10). Secondary hyperparathyroidism occurs with vitamin D deficiency, and serum PTH has been linked to falls in one previous retrospective study (11).

Although much of the focus on biochemical aspects of falls risk has concentrated on vitamin D, there are data supporting an independent effect of PTH on muscle. For example, muscle biopsies obtained in patients suffering from primary hyperparathyroidism have demonstrated type II muscle fiber atrophy (12). In addition, PTH increases proteolysis of muscle proteins and thereby augments the liberation of the amino acids, alanine and glutamine (13). Treatment with PTH has been shown to reduce the intracellular content of inorganic phosphate and calcium-adenosine triphosphatase in rat muscle cells (14), and mRNA for the PTH/PTH-related peptide receptor has been founded in rat muscle tissue (15).

There have been few prospective studies of the relationship among vitamin D status, PTH, and falls. In this study we measured serum 25-hydroxyvitamin D (25OHD), PTH, and objective measures of risk of falls at baseline in a frail elderly institutionalized population and their relationship to falls assessed prospectively.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects

Older people residing in intermediate-care hostels and nursing homes in northern Sydney, Australia, were visited and invited to participate. Individuals who were bed-bound, bilateral amputees, non-English speaking, or under the age of 65 yr were not included in the study, but significant comorbidity was not an exclusion criteria. Eligible residents gave informed consent or, if unable, their next of kin gave proxy consent. Ethics approval was given by the institutional human research ethics committee. Institutions were visited in random order, and in total, 2005 residents were recruited. The participation rate of eligible residents was 55% (self consent, 77%; proxy, 33%). The study is referred to as the FREE study (Fracture Risk Epidemiology in the Elderly) (16, 17). This report is restricted to those participants who were ambulatory and required low care, and comprises data for 646 subjects who had completed at least 3 months of follow-up and for whom baseline serum vitamin D and PTH measurements were available. There were no differences between participants and nonparticipants in gender, age, and type of institution or in time living there (all P > 0.15). The mean duration of follow-up was 10.2 months (the 25th percentile was 7.2 months and the 75th percentile was 12 months).

Clinical biochemistry

At the time of measurement of falls risk, a blood sample for measurement of serum 25OHD and PTH was collected. Specimens for this study were stored as aliquots immediately after centrifugation at –40 C, and only a single freeze-thaw cycle was involved before assay. Serum 25OHD was measured using a specific RIA after an initial extraction kit (DiaSorin, Inc., Stillwater, MN). The assay has a sensitivity of 4 nmol/liter, with an intraassay precision of 7.6% and an interassay precision of 9.0%. The laboratory reference range is 39–140 nmol/liter.

Serum levels of intact PTH were determined by a two-site chemiluminescent ELISA on an Immulite 1000 analyzer (Diagnostic Products, Los Angeles, CA). The assay procedure measures the intact PTH molecule. The sensitivity of this assay is 1 pg/ml, and cross-reactivity to PTH fragments and related compounds is low. The assay has a typical intraassay precision of 5.5%, an interassay precision of 7.9%, and the laboratory reference range is 23–66 pg/ml.

Serum calcium was measured by colorimetric assay (Roche, Indianapolis, IN) using p-cresolphthalein and adjusted for circulating albumin levels, with a normal range 2.15–2.55 mmol/liter. A modified Jaffé (picric acid) kinetic colorimetric assay was used to measure serum creatinine, with a normal range in males of 70–110 µmol/liter and in females of 50–90 µmol/liter. Inorganic phosphorus levels were measured by an end-point method with sample blanking, based on the formation of ammonium phosphomolybdate complex. The normal range in this laboratory is 0.6–1.3 mmol/liter. Serum albumin was measured by a BCG colorimetric assay (Roche), with a normal range of 40–50 g/liter. Measurements of serum calcium, creatinine, inorganic phosphorus, and albumin were only available in a subsample of 264 subjects.

Clinical risk factors

Clinical risk factors were assessed in all subjects at interview, including age, sex, weight, height, presence or absence of incontinence, and medication use. The level of care was ascertained from the Resident Classification Scale (RCS), an eight-point classification instrument that determines the level of government subsidy for each resident. It is based on care need and is weighted for behavioral changes associated with dementia (18). Illness severity was assessed using a modification of the Implicit Illness Severity Scale, in which residents were classified on a four-point scale, where 1 indicated no symptoms, 2 indicated mild symptoms or conditions, 3 indicated moderate symptoms or conditions, and 4 indicated seriously ill (19). Cognitive status was assessed with the Standardized Mini Mental Status Examination (SMMSE) (20).

Standing balance was assessed using the static balance test (5), simplified for this population with a high prevalence of instability by removing the eyes-closed standing conditions. Subjects were classified into five grades: grade 1, unable to stand on the floor for any period without support from another person or use of a walking aid; grade 2, unable to maintain balance on the floor for 30 sec; grade 3, capable of maintaining balance on the floor for 30 sec, but unable to maintain balance on a compliant foam rubber mat (70 x 60 x 15 cm thick) for any period of time; grade 4, capable of maintaining balance on the floor, but unable to maintain balance on the foam rubber mat for 30 sec; and grade 5, capable of maintaining balance when standing on the floor and the foam mat for 30-sec periods. Postural sway (5) was also assessed while subjects underwent the static balance test. Visual contrast sensitivity was assessed using the Melbourne Edge Test (21). Proprioception was measured using a lower limb-matching task (5). Knee extension strength was measured isometrically with subjects seated and the angles of the hip and knee joints positioned at 90° (5). Reaction time was assessed using a light as the stimulus and a finger-press as the response (5). Finally, the subjects’ sit-to-stand ability was measured by assessing their ability to rise from a standard height (0.43 m) chair with armrests (22). Subjects were graded on a four-point scale, where grade 1 indicated capable without the need for arm support, grade 2 indicated capable with the use of the arms, grade 3 indicated capable with the help of another person, and grade 4 indicated incapable. The reliability of these tests has been established in previous studies (21, 22, 23). Fifty-six subjects did not undergo the sit-to-stand test, as this test was not introduced until shortly after the commencement of the study.

Statistical analysis

As a high degree of care provided by nursing staff might influence fall results in subjects with high RCS grades, all analyses were limited to subjects with RCS above 4 (low care). The data were censored at 1 yr. Comparisons between fallers and nonfallers were made with two sample tests. Serum PTH was transformed to a normal distribution using the natural logarithm. Partial correlations were used to determine an association between two variables while adjusting for other variables. Cox proportional hazards models were used to calculate and determine relations between PTH, 25OHD, and time to first fall while adjusting for potential confounders. Interactions between PTH, 25OHD, and other variables were tested in models. In all analyses a value of P < 0.05 (two-tailed) was considered significant.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Three subjects with primary hyperparathyroidism and six subjects with severe renal impairment (serum creatinine, >320 µmol/liter) were excluded from analyses. The diagnosis of primary hyperparathyroidism was based on the presence of elevated serum calcium and PTH levels. The study sample comprised 121 men and 516 women. Two hundred and seventy-four residents fell one or more times in the follow-up period. Of these, 135 fell once only, 56 fell twice, 26 fell three times, 16 fell four times, and 41 fell five or more times. The median time to first fall was 115 d. Table 1Go shows baseline characteristics of fallers vs. nonfallers. Fallers were older, more incontinent, and had difficulty in standing up, poorer balance, poorer proprioception, slower reaction time, weaker quadriceps strength, greater body sway, impaired visual contrast, impaired cognition, higher illness severity rating, higher PTH, and lower 25OHD. Vitamin D deficiency (defined as a serum 25OHD <39 nmol/liter) was present in 64.5% of the men and 75.8% of the women. Serum PTH levels were above the upper reference range level in 29.8% of the men and 46.2% of the women.


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  		TABLE 1. Baseline characteristics by fall status: mean (SD) unless otherwise specified

 
Table 2Go shows correlations of 25OHD (or PTH) with objective measures of falls risk after correcting for gender and for gender and PTH (or 25OHD). The negative correlation between 25OHD and PTH was statistically significant. The association between 25OHD and balance or sit-to-stand was also significant. However, the relationship between 25OHD and sit-to-stand disappeared after adjusting for both PTH and gender. PTH was significantly associated with quadriceps strength and sit-to-stand, but not with balance, when correcting for both 25OHD and gender.


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  		TABLE 2. Partial correlations between 25OHD or PTH and some falls risk characteristics, controlling for gender only or gender and PTH or 25OHD

 
25OHD [hazard ratio (HR), 0.988; 95% confidence interval (CI), 0.980–0.996; P = 0.005] and ln PTH (HR, 1.34; 95% CI, 1.12–1.60; P < 0.001) were both significant predictors of time to first fall. After adjusting for age, incontinence, and illness severity, 25OHD was no longer a significant risk factor for falls (HR, 0.992; 95% CI, 0.984–1.000; P = 0.06). There was an interaction term between PTH and age in multivariate models. As a result, the data were stratified into two groups by age (<90 or >=90 yr). For those who were less than 90 yr old, in a multivariate analysis that included PTH, 25OHD, balance, SMMSE, incontinence, and implicit illness severity, PTH (HR, 1.43; 95% CI, 1.12–1.82; P = 0.004), balance (P < 0.001), SMMSE (P = 0.04), incontinence (P = 0.01), and illness severity (P = 0.02) remained significant predictors, but 25OHD did not (P = 0.62; Table 3Go). The effect of PTH on falls persisted after adding quadriceps strength or sit-to-stand or other biochemical variables, such as calcium, phosphate, albumin, or calculated creatinine clearance, to the model. However, there were only 181 subjects who were 90 yr of age or older, and the association between PTH and falls was not significant (HR, 1.01; 95% CI, 0.76–1.35; P = 0.95) for these subjects in a univariate analysis.


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  		TABLE 3. Multivariate model of association with falls

 
To further examine the relationship among vitamin D status, PTH, and falls, we divided study subjects into four groups: group 1, 25OHD below 39 nmol/liter and PTH above 66 pg/ml; group 2, 25OHD below 39 nmol/liter and PTH of 66 pg/ml or less; group 3, 25OHD of 39 nmol/liter or more and PTH above 66 pg/ml; and group 4, 25OHD of 39 nmol/liter or more and PTH of 66 pg/ml or less. The study population consisted of 34.3%, 39.3%, 8.8%, and 17.6% for groups 1, 2, 3, and 4, respectively. Group 1 was 1.65 times (95% CI, 1.10–2.46; P = 0.02) more likely to have a fall than group 4 after adjustment for age, incontinence, and illness severity in a survival analysis. There were no differences in time to first fall between group 4 and group 3 (HR, 1.03; 95% CI, 0.59–1.81; P = 0.92) or group 2 (HR, 1.30; 95% CI, 0.87–1.94; P = 0.20). These outcomes did not change after adding SMMSE and/or balance to the model.


   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
This study of a large number of frail elderly men and women living in aged cared facilities found a high prevalence of vitamin D deficiency, and that serum PTH was a significant predictor of time to first fall, independent of serum 25OHD. The adjusted hazards ratio for ln PTH was 1.43 (95% CI, 1.12–1.82; P = 0.004), which can be calculated to result in a 30% increase in the risk of falling with a doubling of the PTH level. The effect of PTH on time to first fall was also independent of renal function, calcium level, and nutrition status. However, this effect did not extend to those over 90 yr of age. This may be explained by the very high risk of falling in this older subpopulation. The additional effect of PTH on falls added only a small proportion to their total risk of falling, which the study did not have power to detect.

This is the first large prospective study to observe a relationship between falls and serum PTH. In a prior retrospective cross-sectional study of 83 residents of nursing home and intermediate-care hostels living in Melbourne, Australia, higher serum PTH was independently associated with falling (11). The median age of that population was 84 yr, and most were vitamin D deficient, with a median serum 25OHD level of 27 nmol/liter. Residents who fell (n = 33) had both lower serum 25OHD levels and higher serum PTH levels, but in a multiple logistic regression, serum PTH remained independently associated with falling [odds ratio (OR), 5.6; 95% CI, 1.7–18.5] per unit of the natural logarithm of serum PTH. Other significant predictors were hostel accommodation (OR, 0.04; 95% CI, 0.01–0.25) and ability to walk without aids (OR, 0.07; 95% CI, 0.01–0.37).

The relationship we observed among PTH, 25OHD, and objective measures of falls risk are of interest in terms of the potential mechanism of PTH-mediated falls risk. The inverse correlations we observed between PTH and quadriceps strength and rising from a chair may suggest that the effect of PTH is mediated by diminished muscle function. In a prospective cross-sectional study (10), 60 patients were recruited from a falls clinic and stratified according to serum 25OHD: group 1, 25OHD below 30 nmol/liter; group 2, 25OHD between 30–42.5 30 nmol/liter; and group 3, 25OHD above 42.5 nmol/liter. Twenty healthy elderly volunteers with 25OHD above 42.5 nmol/liter comprised group 4. Group 1 had the greatest degree of postural sway and the weakest quadriceps strength, although this did not reach significance. Multivariate analysis revealed 25OHD as an independent variable for postural sway, but PTH was an independent variable associated with muscle strength, with fallers having higher PTH values. In a prospectively randomized, placebo-controlled trial in vitamin D-deficient older women (mean serum 25OHD, 23 nmol/liter), short-term supplementation with vitamin D and calcium decreased plasma PTH by 18% (P = 0.04) and body sway by 9% (P = 0.04), while there was a 50% reduction in falls (P = 0.03), compared with the placebo group (24).

Vitamin D was not significantly associated with falls after correcting for age, incontinence, and illness severity in this study (P = 0.06). However, a relationship between 25OHD and balance was observed. A number of previous studies have found a relationship between serum 25OHD and falls (8, 9, 10, 25) and between vitamin D and neuromuscular function (8, 9, 10). In contrast, low serum vitamin D levels did not predict new onset of disability or loss of muscle strength in older women in an observational study (26). However, vitamin D deficiency is only one factor contributing to muscle weakness in the elderly (27, 28). The effect of 25OHD on falls via effects on neuromuscular function may be obscured by a high level of chronic illness, medication use, and cognitive disorders in this population. In a recent large prospective study (25), a low level of serum vitamin D was independently associated with time to first fall, but the association was not apparent in nursing home residents, and serum PTH was not measured. In our study we observed that the subjects with low 25OHD land elevated PTH levels were 65% more likely to have a fall than those whose 25OHD and PTH levels were in the normal range. In contrast, those participants with either low 25OHD or high PTH levels did not have a significantly elevated risk of falling.

This study has certain strengths and limitations. The inclusion of nursing home and intermediate-care residents allowed examination of falls in a high risk cohort, but the findings may not be generalizable to more able elderly subjects. Moreover, as serum 25OHD and PTH are closely related, it may be difficult to completely separate the effects of elevated serum PTH from low serum 25OHD on falls, even with sophisticated statistical analyses.

In summary, serum PTH seems to be an independent predictor of time to first fall in the frail elderly. However, the relationship between serum PTH, independent of vitamin D status, and a number of measures of general health on falls risk observed in this study suggests that the biochemical mechanisms associated with secondary hyperparathyroidism and muscle are complex and require further investigation.


   Footnotes
 
Abbreviations: CI, Confidence interval; HR, hazard ratio; 25OHD, 25-hydroxyvitamin D; OR, odds ratio; RCS, Resident Classification Scale; SMMSE, Standardized Mini Mental Status Examination.

Received October 13, 2003.

Accepted January 15, 2004.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Fernie GR, Gryfe CI, Holliday PJ, Llewellyn A 1982 The relationship of postural sway in standing to the incidence of falls in geriatric subjects. Age Ageing 11:11–16[Abstract/Free Full Text]
  2. Lipsitz LA, Jonsson PV, Kelley MM, Koestner JS 1991 Causes and correlates of recurrent falls in ambulatory frail elderly. J Gerontol 46:M114–M122
  3. Yip YB, Cumming RG 1994 The association between medications and falls in Australian nursing-home residents. Med J Aust 160:14–18[Medline]
  4. Thapa PB, Brockman KG, Gideon P, Fought RL, Ray WA 1996 Injurious falls in nonambulatory nursing home residents: a comparative study of circumstances, incidence, and risk factors. J Am Geriatr Soc 44:273–278[Medline]
  5. Lord SR, Clark RD, Webster IW 1991 Physiological factors associated with falls in an elderly population. J Am Geriatr Soc 39:1194–1200[Medline]
  6. Clark RD, Lord SR, Webster IW 1993 Clinical parameters associated with falling in an elderly population. Gerontology 39:117–123[Medline]
  7. Lord SR, Clark RD 1996 Simple physiological and clinical tests for the accurate prediction of falling in older people. Gerontology 42:199–203[Medline]
  8. Pfeifer M, Begerow B, Minne HW 2002 Vitamin D and muscle function. Osteoporos Int 13:187–194[CrossRef][Medline]
  9. Pfeifer M, Begerow B, Minne HW, Schlotthauer T, Pospeschill M, Scholz M, Lazarescu AD, Pollahne W 2001 Vitamin D status, trunk muscle strength, body sway, falls, and fractures among 237 postmenopausal women with osteoporosis. Exp Clin Endocrinol Diabetes 109:87–92[CrossRef][Medline]
  10. Dhesi JK, Bearne LM, Moniz C, Hurley MV, Jackson SH, Swift CG, Allain TJ 2002 Neuromuscular and psychomotor function in elderly subjects who fall and the relationship with vitamin D status. J Bone Miner Res 17:891–897[CrossRef][Medline]
  11. Stein MS, Wark JD, Scherer SC, Walton SL, Chick P, Di Carlantonio M, Zajac JD, Flicker L 1999 Falls relate to vitamin D and parathyroid hormone in an Australian nursing home and hostel. J Am Geriatr Soc 47:1195–1201[Medline]
  12. Patten BM, Bilezikian JP, Mallette LE, Prince A, Engel WK, Aurbach GD 1974 Neuromuscular disease in primary hyperparathyroidism. Ann Intern Med 80:182–193
  13. Garber AJ 1983 Effects of parathyroid hormone on skeletal muscle protein and amino acid metabolism in the rat. J Clin Invest 71:1806–1821
  14. Baczynski R, Massry SG, Magott M, El-Belbessi S, Kohan R, Brautbar N 1985 Effect of parathyroid hormone on energy metabolism of skeletal muscle. Kidney Int 28:722–727[Medline]
  15. Tian J, Smogorzewski M, Kedes L, Massry SG 1993 Parathyroid hormone-parathyroid hormone related protein receptor messenger RNA is present in many tissues besides the kidney. Am J Nephrol 13:210–213[Medline]
  16. Zochling J, Sitoh YY, Lau TC, Cameron ID, Cumming RG, Lord SR, Schwarz J, Trube A, March LM, Sambrook PN 2002 Quantitative ultrasound of the calcaneus and falls risk in the institutionalized elderly: sex differences and relationship to vitamin D status. Osteoporos Int 13:882–887[CrossRef][Medline]
  17. Lord SR, March LM, Cameron ID, Cumming RG, Schwarz J, Zochling J, Sitoh YY, Chen JS, Makaroff J, Lau TC, Sambrook PN 2003 Differing risk factors for falls in nursing home and intermediate care residents who can and cannot stand unaided. J Am Geriatr Soc 51:1645–1650[CrossRef][Medline]
  18. Cuthbertson S, Lindsay-Smith U, Rosewarne R 1997 Background paper for a review of the Resident Classification Scale (RCS). Canberra: Australian Department of Health and Ageing
  19. Holtzman J, Lurie N 1996 Causes of increasing mortality in a nursing home population. J Am Geriatr Soc 44:258–264[Medline]
  20. Folstein MF, Folstein SE 1975 Mini-Mental State: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 12:189–198[CrossRef][Medline]
  21. Verbaken JH, Johnston AW 1986 Population norms for edge contrast sensitivity. Am J Optom Physiol Opt 63:724–32[Medline]
  22. Seaby L, Torrance G 1989 Reliability of a physiotherapy functional assessment used in a rehabilitation setting. Physiother Can 41:264–271
  23. Lord SR, Clark RD, Webster IW 1991 Postural stability and associated physiological factors in a population of aged persons. J Gerontol 46:M69–M76
  24. Pfeifer M, Begerow B, Minne HW, Abrams C, Nachtigall D, Hansen C 2000 Effects of a short-term vitamin D and calcium supplementation on body sway and secondary hyperparathyroidism in elderly women. J Bone Miner Res 15:1113–1118[CrossRef][Medline]
  25. Flicker L, Mead K, MacInnis RJ, Nowson C, Scherer S, Stein MS, Thomas J, Hopper JL, Wark JD 2003 Serum vitamin D and falls in older women in residential care in Australia. J Am Geriatr Soc, 51:1533–1538
  26. Verreault R. Semba RD. Volpato S. Ferrucci L. Fried LP. Guralnik JM 2002 Low serum vitamin D does not predict new disability or loss of muscle strength in older women. J Am Geriatr Soc 50:912–917[CrossRef][Medline]
  27. Grimby G 1995 Muscle performance and structure in the elderly as studied cross-sectionally and longitudinally. J Gerontol 50A:17–22
  28. Brooks SV, Faulkner JA 1994 Skeletal muscle weakness in old age: underlying mechanisms. Med Sci Sports Exerc 26:432–439[Medline]



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