Serum [25(OH)D] status, ankle strength and activity show seasonal variation in older adults:
relevance for winter falls in higher latitudes
Age Ageing (2012) Received November 27, 2011.; Accepted April 5, 2012.
First published online: May 14, 2012
Marie-Louise Bird1?, Keith D. Hill2, Iain K. Robertson1, Madeleine J. Ball1, Jane Pittaway1 and Andrew D. Williams1
1 School of Human Life Sciences, University of Tasmania, Launceston, Tasmania 7250, Australia
2 School of Physiotherapy, Curtin University, Perth, Western Australia 6845, Australia
Address correspondence to: M.-L. Bird. Tel: (+61) 3 63243123 ; Fax: (+61) 3 63243658. Email: birdm at utas.edu.au
Background: seasonal variation exists in serum [25(OH)D] and physical activity, especially at higher latitudes, and these factors impact lower limb strength. This study investigates seasonal variation in leg strength in a longitudinal repeated measures design concurrently with serum vitamin D and physical activity.
Methods: eighty-eight community-dwelling independently mobile older adults (69.2 ± 6.5 years) were evaluated five times over a year, at the end of five consecutive seasons at latitude 41.1°S. Leg strength, serum [25(OH)D] and physical activity levels were measured. Time spent outside was recorded. Monthly falls diaries recorded falls. Data were analysed to determine annual means and percentage changes.
Results: significant variation in [25(OH)D] (±15%), physical activity (±13%), ankle dorsiflexion strength (±8%) and hours spent outside (±20%) (all P < 0.001) was demonstrated over the year, with maximums in January and February (mid-summer). Low mean ankle strength was associated with increased incidence of falling (P = 0.047). Quadriceps strength did not change (±2%; P = 0.53).
Conclusion: ankle dorsiflexor strength varied seasonally.
Increased ankle strength in summer may be influenced by increased levels of outdoors activity over the summer months.
Reduced winter-time dorsiflexor strength may predispose older people to increased risk of tripping-related falls, and warrants investigation in a multi-faceted falls prevention programme.
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