Nutrition/Obesity
Tracking of serum 25-hydroxyvitamin D levels over 11 years in the Norwegian HUNT study Xiao-Mei Mai* Xiao-Mei Mai Marit Næss Kristin S Sætermo Anne Jorunn Vikdal Yi-Qian Sun
Introduction: Serum 25-hydroxyvitamin D (25(OH)D), a marker of vitamin D status derived from sunlight exposure and diet, may influence various health conditions. This study investigates the tracking of serum 25(OH)D levels over 11 years in a general adult population in Norway and evaluates factors that may affect future serum 25(OH)D levels.
Research Design and Methods: Tracking of serum 25(OH)D levels was conducted among 3511 adults who participated in both the HUNT2 (1995–1997) and HUNT3 (2006–2008) surveys, with an 11-year interval. Serum 25(OH)D levels from HUNT2 and HUNT3 were measured using a chemiluminescent assay and calibrated for batch effect and seasonal variation. Correlation coefficient between the two measurements was calculated, as well as intra-individual variability using the intraclass correlation coefficient (ICC) and coefficient of variation (CV). Multivariable linear regression models were used to estimate the relations between various factors in HUNT2 and 25(OH)D levels in HUNT3.
Results: Findings showed a correlation coefficient of 0.50 (95% CI: 0.47 to 0.52), an ICC of 0.64 (95% CI: 0.56 to 0.70), and a CV of 18% between the two measurements. An average 43% (range: 20.4% to 54.9%) of participants remained in the same vitamin D category (<30.0, 30.0–49.9, 50.0–74.9, and ≥75.0 nmol/L) across both surveys. Male sex, vitamin D-decreasing polygenic score, higher body mass index, and current smoking were associated with lower 25(OH)D levels, while higher education, moderate alcohol intake, and vitamin D supplementation were associated with higher levels.
Conclusions: This study found moderate reliability of serum 25(OH)D levels over an 11-year follow-up period, suggesting that a single measurement may not suffice for long-term vitamin D status assessment. Repeated measurements are desirable for accurate evaluation of vitamin D’s role in chronic disease risk.