Seasonal variation of serum vitamin D and the effect of vitamin D supplementation in Irish community-dwelling older people

• Published in: Age and ageing 2011-03, Vol.40 (2), p.168-174
• Main Authors: Romero-Ortuno, Roman, Cogan, Lisa, Browne, Joseph, Healy, Martin, Casey, Miriam Catherine, Cunningham, Conal, Walsh, James Bernard, Kenny, Rose Anne
• Format: Article
• Language: English
• Subjects: Aged; Aged, 80 and over; Alfacalcidol; Ambulatory Care Facilities; Biomarkers - blood; Calcifediol; Care and treatment; Causes of; Cholecalciferol - therapeutic use; Community living; Cross-Sectional Studies; Dietary Supplements; Dosage; Dosage and administration; Elderly; Female; Geriatric Assessment; Health aspects; Humans; Independent Living; Ireland; Linear Models; Male; Odds Ratio; Older people; Physiological aspects; Radiation; Risk Assessment; Risk Factors; Seasons; Serum; Studies; Sunlight; Treatment Outcome; Ultraviolet Rays; Vitamin D; Vitamin D - analogs & derivatives; Vitamin D - blood; Vitamin D deficiency; Vitamin D Deficiency - blood; Vitamin D Deficiency - etiology; Vitamin D Deficiency - prevention & control; Vitamin deficiency
• ISSN: 0002-0729; 1468-2834
• DOI: 10.1093/ageing/afq138

Ireland 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. 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.