Serum Klotho Modifies the Associations of 25-Hydroxy Vitamin D With All-Cause and Cardiovascular Mortality.

Background: The association between 25-hydroxyvitamin D and mortality remains controversial. Klotho, a biomarker of vitamin D activation and metabolism, may play a key role in this association. However, it is unclear whether the association between vitamin D deficiency and mortality risk is modified by klotho levels. Therefore, this study investigated the joint association of serum 25-hydroxyvitamin D [25(OH)D] and klotho with mortality risk in American community-dwelling adults.

Methods: A total of 9870 adults from the National Health and Nutrition Examination Survey (2007-2016) were included in our study. Mortality data were ascertained by linking participants to National Death Index records. Cox proportional hazards models were used to assess the association among serum 25(OH)D, serum klotho, and all-cause and cardiovascular disease (CVD) mortality.

Results: We found a significant interaction between klotho and serum 25(OH)D in all-cause mortality (P = .028). With klotho > 848.4 pg/mL (risk threshold on mortality), no significant all-cause and CVD mortality risk was observed at any level of serum 25(OH)D. However, with klotho < 848.4 pg/mL, a significant all-cause and CVD mortality risk was observed with serum 25(OH)D < 50 nmol/L [hazards ratio (HR), 1.36; 95% confidence interval (CI), 1.10-1.69; HR, 1.78; 95% CI, 1.16-3.45) and serum 25(OH)D of continuous variable (HR, 0.98; 95% CI, .97-.99; HR, 0.98; 95% CI, .98-.99). In addition, vitamin D metabolism disruption accessed by the combination of decreasing serum 25(OH)D (<50 nmol/L) and klotho (<848.4 pg/mL) was associated with significant all-cause mortality (HR, 1.48; 95% CI, 1.11-1.96) and CVD mortality (HR, 2.36; 95% CI, 1.48-3.75).

Conclusions: Vitamin D-associated mortality risk is observed only with concurrently decreasing klotho, indicating that vitamin D metabolism dysfunction increases the risk of mortality. Klotho levels could help predict long-term mortality outcomes and thus may be useful concurrently for guiding vitamin D supplementation therapy decision-making in populations with vitamin D deficiency.