The Relationship between Total Bilirubin Levels and Total Mortality in Older Adults: The United States National Health and Nutrition Examination Survey (NHANES) 1999-2004

OBJECTIVE Due to its anti-oxidant and anti-inflammatory properties, bilirubin has been associated with reduced cardiovascular risk. A recent study demonstrated an L-shaped association of pre-treatment total bilirubin levels with total mortality in a statin-treated cohort. We therefore investigated the association of total bilirubin levels with total mortality in a nationally representative sample of older adults from the general population. METHODS A total of 4,303 participants aged ≥ 60 years from the United States National Health and Nutrition Examination Survey 1999-2004 with mortality data followed up through December 31, 2006 were included in this analysis, with a mean follow-up period of 4.5 years. RESULTS Participants with total bilirubin levels of 0.1-0.4 mg/dl had the highest mortality rate (19.8%). Compared with participants with total bilirubin levels of 0.5-0.7 mg/dl and in a multivariable regression model, a lower total bilirubin level of 0.1-0.4 mg/dl was associated with higher risk of total mortality (hazard ratios, 1.36; 95% confidence interval, 1.07-1.72; P = 0.012), while higher levels (≥ 0.8 mg/dl) also tended to be associated with higher risk of total mortality, but this did not reach statistical significance (hazard ratios, 1.24; 95% confidence interval, 0.98-1.56; P = 0.072). CONCLUSION In this nationally representative sample of older adults, the association of total bilirubin levels with total mortality was the highest among those with a level between 0.1 and 0.4 mg/dl. Further studies are needed to investigate whether higher total bilirubin levels could be associated with a higher mortality risk, compared to a level of 0.5-0.7 mg/dl.