Seasonal variation of serum vitamin D and the effect of vitamin D supplementation in Irish community-dwelling older people.
Casey, Miriam Catherine
Walsh, James Bernard
Kenny, Rose Anne
AffiliationTrinity College Dublin-TRIL Clinic, Hospital, St James's Hospital, Dublin 8, Co. Dublin, Ireland. email@example.com
Aged, 80 and over
Ambulatory Care Facilities
Vitamin D Deficiency
MetadataShow full item record
CitationSeasonal variation of serum vitamin D and the effect of vitamin D supplementation in Irish community-dwelling older people. 2011, 40 (2):168-74 Age Ageing
JournalAge and ageing
AbstractIreland is at 53°N, and its population risk of vitamin D deficiency is high. Previous Irish studies suggested a significant seasonality of serum 25-hydroxyvitamin D [25(OH)D] and a beneficial effect of supplementation in raising 25(OH)D levels. However, in Irish older people, little is known about the magnitude of the supplementation effect and whether supplementation affects 25(OH)D seasonality.
cross-sectional observational. Setting: outpatient clinic.
five hundred and forty-six community-dwelling subjects (mean age 73.0, SD 7.4; 68.5% females) were assessed between September 2007 and May 2009.
for supplemented and non-supplemented: 'cosinor' analysis (Pulse_XP®) of monthly 25(OH)D. Period global solar radiation (GSR) and solar elevation angle (SEA) data were collected as proxy markers of ultraviolet-B radiation exposure. Multivariate linear regression was conducted to investigate the independent effect of GSR and SEA on 25(OH)D, controlling for confounders.
supplemented group (N = 183): 89.1% were on cholecalciferol 800 IU/day. Mean 25(OH)D = 64.1 (95% confidence interval: 52.2-75.8) nmol/l, with no significant seasonality; regression: neither GSR nor SEA predicted 25(OH)D. Non-supplemented group (N = 363): mean 25(OH)D = 40.3 (35.5-45.0) nmol/l, with significant seasonality (55.5% variance remaining), peak in August, amplitude = 6.0 (3.1-8.8) nmol/l; regression: both GSR (P = 0.002) and the interaction GSR * SEA (P = 0.018) predicted 25(OH)D.
vitamin D supplementation was associated with a mean serum 25(OH)D increase of 23.8 nmol/l. Interestingly, supplementation seemed to blunt seasonality. In the supplemented group, 72.1% had individual 25(OH)D levels below the recommended 75 nmol/l. There is a case for universal supplementation in Irish older people, probably at a higher dose. Further research is needed to establish the optimum dose.
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