Faculdade de Ciências da Nutrição e Alimentação da Universidade do Porto Rua Dr. Roberto Frias, 4200-465, Porto, Portugal.
I3S-Instituto de Investigação e Inovação em Saúde, R. Alfredo Allen, 4200-135, Porto, Portugal.
BMC Geriatr. 2017 Oct 31;17(1):256. doi: 10.1186/s12877-017-0644-8.
The older population is a risk group for hypovitaminosis D. The Ultraviolet Index (UVI) can be an indicator of potential for cutaneous synthesis of vitamin D but physiological and other environmental factors also influence vitamin D synthesis and status. Knowledge about vitamin D status in Portuguese older adults is limited. This study aims to explore the association between Ultraviolet Index and serum 25-hidroxyvitamin D3 [25(OH)D] levels accounting for other potential influential factors.
A cross-sectional study was conducted between December 2015 and June 2016, in 1497 Portuguese older adults (≥ 65 years) within Nutrition UP 65 project. For each participant, serum 25(OH)D was determined and the mean UVI (mUVI) in the respective residence district was calculated for the previous 30 days. Stepwise linear regression analyses were conducted for the following periods of blood collection: between December and June, December and March and April and June. Standardized regression coefficients (Sβ) and 95% confidence intervals were calculated.
The median 25(OH)D concentration was 35.9 nmol/L. The UVI was independently and positively associated with 25(OH)D in the models for December-June (Sβ = 0.244, 95% CI: 0.198; 0.291, P < 0.001) and April-June (Sβ = 0.295, 95% CI: 0.299; 0.362, P < 0.001) and independently and negatively associated in December-March period (Sβ = -0.149, 95% CI: -0.211; -0.087, P < 0.001).
In this sample with high vitamin D deficiency frequency, the UVI was a predictor of 25(OH)D levels but the direction of the association varied according to the blood collection period. Our results suggest that accounting for the time of year in future research regarding vitamin status and related public health recommendations may be relevant.
老年人是维生素 D 缺乏症的高危人群。紫外线指数（UVI）可以作为皮肤合成维生素 D 的潜在指标，但生理和其他环境因素也会影响维生素 D 的合成和状态。有关葡萄牙老年人维生素 D 状况的知识有限。本研究旨在探讨紫外线指数与血清 25-羟维生素 D3 [25(OH)D]水平之间的关系，同时考虑其他潜在的影响因素。
本研究为 2015 年 12 月至 2016 年 6 月间进行的一项横断面研究，共纳入 1497 名葡萄牙老年人（≥65 岁），来自营养 UP 65 项目。对每位参与者，测定其血清 25(OH)D 浓度，并计算其居住地前 30 天的平均紫外线指数（mUVI）。分别对以下采血时间段进行逐步线性回归分析：12 月至 6 月、12 月至 3 月和 4 月至 6 月。计算标准化回归系数（Sβ）和 95%置信区间。
血清 25(OH)D 浓度的中位数为 35.9 nmol/L。在 12 月至 6 月和 4 月至 6 月的模型中，UVI 与 25(OH)D 呈独立且正相关（Sβ分别为 0.244、95%CI：0.198；0.291，P<0.001），而在 12 月至 3 月的模型中，UVI 与 25(OH)D 呈独立且负相关（Sβ=-0.149、95%CI：-0.211；-0.087，P<0.001）。
在这个维生素 D 缺乏频率较高的样本中，紫外线指数是 25(OH)D 水平的预测因子，但关联的方向随采血时间的不同而变化。我们的研究结果表明，在未来关于维生素状况及相关公共卫生建议的研究中，考虑到季节时间因素可能是相关的。
