Epub: Saltytė Benth et al. Modelling and Prediction of 25-Hydroxyvitamin D Levels in Norwegian Relapsing-RemittingMultiple Sclerosis Patients. Neuroepidemiology. 2012 Jul ;39(2):84-93.
Background/Aim: 25-Hydroxyvitamin D (25(OH)D) levels are suggested to influence the susceptibility and risk of disease progression in MS. Seasonal fluctuation of 25(OH)D levels may differ in magnitude between individuals. The purpose of this paper was to model the seasonal fluctuation of vitamin D in Norwegian MSers and to examine to which extent one single 25(OH)D measurement predicts the level at other time points throughout the year.
Methods: During December 2004 and July 2008, 762 serum samples were collected from 92 Norwegian relapsing-remitting MSers. Time series analysis and multivariate modelling techniques were used to model seasonal fluctuations and intra- and inter-individual variations in 25(OH)D values.
Results: Most MSers reached their lowest 25(OH)D level in March/April and the highest in July/August. There were substantial intra-individual variations in the extent of seasonal fluctuation, with 36.6% of explainable variation in seasonally adjusted 25(OH)D levels (on a logarithmic scale) attributable to the MSer level. The remaining 63.4% could be accounted for by sources of inter-individual variation. Both the total and inter-individual variabilities were lowest in February, and the prediction interval in this month was up to 26% narrower compared to other months. The prediction intervals would be at least 21% wider with only one observation available per patient.
Conclusions: The seasonal fluctuations of 25(OH)D levels in Norwegian relapsing-remitting MSers are subject to pronounced intra- and inter-individual variation. The most representative measurements of 25(OH)D levels are taken in February.
"This study has tried to overcome the seasonal variation in vD levels in MSers. As you are aware levels are lowest at the end of winter and highest at the end of summer. Can one overcome this by taking on level and then calculating an average level for the year? Yes, is the answer but is only an approximate and is subject to other variables, e.g. genetic variability and diet. Despite this the author's have concluded that the level at the end of winter is the best one to measure."
Labels: Vitamin D