Factors Associated With Change in 25-Hydroxyvitamin D Levels Over Longitudinal Follow-Up in the ARIC Study.

Context: A single measurement of 25-hydroxyvitamin D (25 [OH] D) may not accurately reflect long-term vitamin D status. Little is known about change in 25(OH)D levels over time, particularly among blacks.
Objective: The objective of the study was to determine the longitudinal changes in 25(OH)D levels among Atherosclerosis Risk in Communities (ARIC) study participants.
Design: This was a longitudinal study.
Setting: The study was conducted in the general community.
Participants: A total of 9890 white and 3222 black participants at visit 2 (1990-1992), 888 whites and 876 blacks at visit 3 (1993-1994), and 472 blacks at the brain visit (2004-2006) participated in the study.
Main Outcome Measure: The 25(OH)D levels were measured, and regression models were used to assess the associations between clinical factors and longitudinal changes in 25(OH)D.
Results: Vitamin D deficiency (<50 nmol/L [<20 ng/mL]) was seen in 23% and 25% of whites at visits 2 and 3, and in 61%, 70%, and 47% of blacks at visits 2, 3, and the brain visit, respectively. The 25(OH)D levels were correlated between visits 2 and 3 (3 y interval) among whites (r = 0.73) and blacks (r = 0.66). Among blacks, the correlation between visit 2 and the brain visit (14 y interval) was 0.33. Overall, increases in 25(OH)D levels over time was associated with male gender, use of vitamin D supplements, greater physical activity, and higher high-density lipoprotein-cholesterol (P < .001). Decreases in 25(OH)D levels over time were associated with current smoking, higher body mass index, higher education, diabetes, and hypertension (all P < .05).
Conclusions: Among US blacks and whites, 25(OH)D levels remained relatively stable over time. Certain modifiable lifestyle factors were associated with change in 25(OH)D levels over time.