University of Tasmania

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Long-term follow-up of determinants of seasonal variation in vitamin D status in older adults

Background/Aims: To investigate behavioural impact on long-term seasonal vitamin D status in older Tasmanian adults.

Methods: Seventy participants in a study investigating determinants of vitamin D status returned for follow-up assessment nine months (winter) and 26 months (summer) after study completion (21 male, 49 female; aged 69.2 ± 6.4 years, range 60-84 years). Changes in diet, supplement use, time spent outside, sun protection and serum vitamin D concentration were compared between four time points (summer and winter during the study, winter and summer follow-up) using repeated measures mixed effects linear regression.

Results: Serum vitamin D (± 1SD nmol/L) in summer during-study (68.8 ± 22.1) was significantly higher (P < 0.001) than winter during-study (52.6 ± 20.9) and significantly lower (P < 0.001) than summer follow-up (78.5 ± 16.7) but not different to winter follow-up (65.8 ± 18.3). Winter during-study was significantly lower (P < 0.001) than all other time-points. During the study, 15/70 participants ingested vitamin D supplements. At nine and 26 months it was 38/70 and 42/70. There was a significant difference in vitamin D status between supplement and non-supplement groups during-study and winter follow-up (P < 0.04); however, summer follow-up results were not different between the two groups (P = 0.39). Over the three-year timespan there was a slight but significant increase in intake of cheese and dairy-based foods (eg fromage frais and custards) (P < 0.001) but time spent outside reduced significantly (P&nbp; <0.001). Sun protection behaviours differed between summer and winter only (P < 0.001).

Conclusions: The major behavioural change responsible for increased vitamin D status post-study was the increase in supplement use.



School of Nursing

Event title

Thirty-Eighth Annual Scientific Meeting of The Nutrition Society of Australia

Event Venue

Hobart, Tasmania

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Date of Event (End Date)


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