Background The link between total cholesterol (TC) and all-cause and specific mortality has not been elucidated. Herein, we aimed to evaluate the effect of TC levels on all-cause, cardiovascular disease (CVD), and cancer mortality. Methods All data analyzed were obtained from the National Health and Nutrition Examination Survey 1999–2014. The relationship between levels of TC and mortality was determined through Cox proportional hazard regression analysis coupled with multivariable adjustments. Two-piecewise linear regression models and Cox models with penalized splines were applied to explore nonlinear and irregular shape relationships. Kaplan–Meier survival curve and subgroup analyses were conducted. Results The sample studied comprised 14,662 men and 16,025 women, categorized as 25,429 adults aged 18–65 and 5,258 adults over 65 years old. A total of 2,570 deaths were recorded. All-cause, cardiovascular, and cancer mortality showed U-curve associations after adjusting for confounding variables in the restricted cubic spline analysis. Hazard ratios (HRs) of all-cause and cancer mortality were particularly negatively related to TC levels in the lower range < 200 mg/dL, especially in the range < 120 mg/dL (HR 1.97; 95% CI 1.38, 2.83, HR 2.39; 95% CI 1.21, 4.71, respectively). However, the HRs of cardiovascular disease mortality in the range < 120 mg/dL were the lowest (HR 0.60; 95% CI 0.15, 2.42). In the upper range, a TC range of ≥ 280 mg/dL was correlated with mortality as a result of CVD and cancer (HR 1.31; 95% CI 0.87, 1.97 and HR 1.22; 95% CI 0.82, 1.79). The lowest cumulative survival rate of all-cause mortality was recorded in the lowest TC-level group, while the lowest cumulative survival rate of CVD mortality was recorded in the highest TC-level group. Conclusions A nonlinear association of TC level with all-cause, cancer, and CVD mortality in the American population was observed, suggesting that too low or too high serum total cholesterol levels might correlate with adverse outcomes.

Background The relationship between triglyceride (TG) level and the mortality risk of all-cause and cardiovascular disease is not entirely consistent among adults. Methods The present analysis included adult participants from National Health and Nutrition Examination Surveys (NHANES) between the periods 1999–2014. The levels of TG were categorized into < 150, 150–199, 200–250 and ≥ 250 mg/dL respectively. Multivariate Cox regression analysis, stratified analysis and generalized additive model were conducted to reveal the correlation between TG and mortality risk. Results were presented in hazard ratio (HRs) and 95% confidence intervals (CIs). Results There were 18,781 (9130 males, mean age was 45.64 years) participants being included in the analysis. The average follow-up period was 8.25 years, where 1992 (10.61%) cases of all-cause and 421 (2.24%) cardiovascular death have occurred. In the multivariate Cox model, every 1 mg/dL raise in TG has significantly associated with all-cause mortality (HR: 1.08, 95% CI: 1.02, 1.15) but not cardiovascular mortality (HR: 1.10, 95% CI: 0.97, 1.24). When using TG <  150 mg/dL as reference, TG ≥ 250 mg/dL associated with death from all-cause (HR = 1.34, 95% CI: 1.12, 1.60; P = 0.0016 but not cardiovascular death (HR = 1.26, 95% CI: 0.85, 1.88; P = 0.2517). According to smoothing spline plots, the risk of all-cause was the lowest when TG was approximately 135 mg/dL. Conclusion TG might have a dose-independent association with all-cause mortality among adults in United States.