Serum vitamin D concentrations and unexplained elevation in ALT among US adults.

Background: Low serum levels of vitamin D are associated with metabolic syndrome. Participants in NHANES III with unexplained elevation in ALT levels have high prevalence of metabolic syndrome. We hypothesized that the serum concentrations of vitamin D were inversely associated with unexplained elevation in ALT.

Methods: A total of 6,826 fasting subjects underwent morning physical examination and met the inclusion and exclusion criteria. From these participants, we have constructed cases with unexplained elevation in ALT (n = 308) and compared their serum vitamin D concentrations to matched controls with normal ALT (N = 979). We examined the prevalence of unexplained elevation in ALT level across different quartiles of vitamin D levels.

Results: Participants with unexplained elevation in ALT had significantly lower serum vitamin D levels compared to controls (61.8 ± 26.0 nmol/l vs. 66.8 ± 27.1 nmol/l, P < 0.01). The unadjusted prevalence of unexplained elevation in ALT in patients with highest to lowest quartiles of serum vitamin D levels were 21.4, 21.4, 25.6, and 31.5%, respectively. Compared to lowest quartile, patients with top two quartiles of serum vitamin D levels had significantly lower prevalence of unexplained elevation in ALT (OR, 95% CI for highest quartile 0.62 [0.43-0.89] and for third quartile 0.61 [0.42-0.86]). This relationship persisted even after controlling for metabolic syndrome, insulin resistance, and serum triglycerides.

Conclusions: This study suggests a significant inverse relationship between serum vitamin D levels and unexplained elevation in ALT. Further studies are needed to confirm this observation and to understand the basis for and implications of this observation.