Full length articleVitamin D and parathyroid hormone are associated with gait instability and poor balance performance in mid-age to older aged women
Introduction
Specific hormones play an important role in musculoskeletal health and in fall and fracture prevention in older adults. Poor vitamin D status (as determined by low serum 25 hydroxyvitamin D (25-OHD) concentration) and high levels of parathyroid hormone (PTH) have been implicated in sarcopenia and loss of muscle strength [1], and may also influence other fall risk factors such as motor control of gait and dynamic balance control. The inter-relationship between PTH, 25-OHD levels and gait parameters is currently unclear [2]. Although supplementation with vitamin D has been shown to improve leg muscle strength [3], postural sway and functional tasks (for example, the Timed Up and Go test), the impact of supplementation on specific balance tasks is less clear [2]. Either in association with low levels of vitamin D or independently, the role of PTH in these fall risks factors remains less clear [4].
Vitamin D levels and accidental falling have been the subject of considerable investigation, largely in frail older people, producing non-linear and conflicting results with differences depending on the functional status of the populations investigated. Current theory supports a relationship which is U-shaped, with both very high and very low levels related to increased rates of falls [5]. Mechanisms for the increased fall rates at both ends of the curve may be different; for higher functioning people, high levels of physical activity and ‘risk’ associated with some activities may account for this higher fall rate at higher levels of 25-OHD. At the older and frailer end of the spectrum, the lower levels of 25-OHD associated with falling [5] may relate to reduced strength and muscle mass [1]. However, the roles of 25-OHD and PTH in neural control are less clear.
There is considerable debate as to the level of 25-OHD that maximally suppresses PTH; it is estimated to vary between 25 and 122 nmol/L [6], [7]. More importantly, there is evidence that, in an older cohort, increases in PTH may independently play a role in physiological functioning of muscle and neural tissue, but this area has not been well investigated across the life-course. PTH has been shown to relate to handgrip strength and not balance [8], and more recently the same authors found no relationship between PTH and mobility limitations [9]. While the PTH response to low levels of 25-OHD appears to be a good marker of functional outcomes [10], and a predictor of morbidity and mortality [11], there is increasing evidence that PTH may act independently of vitamin D in adverse health outcomes [12] [13]. For example, PTH predicts mortality independently of vitamin D levels in community-dwelling older adults [14] and in frail older adults [15]. Recently, PTH and not 25-OHD have been found to be associated with gait stability parameters in an older cohort (mean age 81 years) [16].
In relation to falls, serum PTH levels predict time to first fall in a frail population [17]. Higher PTH and lower 25-OHD were reported in long-term care or assisted-living facility residents who had fallen [18]. While PTH was significantly higher in the group who had fallen (mean PTH (SD): fallers = 3.55 ng/L (2.44) vs. non-fallers = 3.32 ng/L (2.05); p = 0.041), no association between 25-OHD and fall rates was found once data were adjusted for high PTH levels. This reinforces the importance of PTH, and suggests that low levels of 25-OHD may increase falls risk only when combined with elevated levels of PTH in a frail older population [4].
The relationship between PTH, vitamin D and falls in healthier mid-age to older people remains less investigated than in frail groups, and it is important to also examine relationships between PTH levels specifically among vitamin D replete adults to determine whether independent action of this hormone on fall risk is present. Thus, the purpose of this study was to investigate the relationship between PTH and 25-OHD levels and clinical tests of gait stability and dynamic balance with respect to their role as physical fall risk factors in adults over 45 years old. It was hypothesized that high levels of PTH and low levels of serum 25-OHD would be significantly associated with poorer gait and dynamic balance performance.
Section snippets
Study participants
Participants who were female twins over the age of 45 years who had previously participated in heritability studies recruited from the Australian Twin Registry (ATR) and Twin Research Program at the Royal Melbourne Hospital (Melbourne, Victoria, Australia) were invited to take part in this study. Those with major musculoskeletal or any neurological disorders or without a good understanding of the English language were excluded. Screening was undertaken to ensure that no neurological balance
Results
Of the 252 women approached (126 pairs) to participate in the study, 122 participants were recruited (61 pairs, 48% response rate). Three participants were unable to supply a blood sample, giving a total of 119 women between the ages of 47 and 80 (mean 59.4 ± 8.2) years with a mean BMI of 26.3 (SD 4.6). All participants were living in the State of Victoria, Australia, with the majority (58.0%) of the sample living in Melbourne (38° South). Eighty-six percent of participants regarded their general
Discussion
The main objective of this study was to determine whether levels of PTH and 25-OHD were associated with performance on gait and balance measures in apparently-healthy older women with no neurological balance disorder. In this cohort, it was found that both PTH and 25-OHD were significantly associated with gait stability (DSD), and 25-OHD was significantly associated with dynamic balance performance. Findings from this study suggest that higher PTH was associated with poorer gait performance
Conflict of interest
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed.
Acknowledgements
Funding received by the co-authors that part funded this project include;
Cohort studies of bone density change in female twins. NH&MRC Research Project Grant. JD Wark, CA Nowson, JL Hopper. ($464,953)
Cohort studies of bone density change in female twins. VicHealth Research Program. JD Wark, CA Nowson, JL Hopper. ($86,036)
A study of the heritability of balance using a cohort of postmenopausal twins. Rebecca L. Cooper Medical Research Foundation. JD Wark, AM Cassano, K Hill. (8000)
A study of the
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