Associations between smoking, glucose metabolism and lipid levels: A cross-sectional study

The aim of this study was to investigate glucose profiles assessed by oral glucose tolerance tests (OGTT), fasting glucose, and lipid profiles among smokers, ex-smokers and never-smokers.

The study design used was a cross-sectional analysis of data from several years of the NHANES (National Health and Nutrition Examination Survey) from 2005 to 2014. A total of 12,460 participants with measures of OGTT, triglycerides, LDL-cholesterol and HDL-cholesterol were included for the data analysis. Outcomes were all assessed in an unadjusted and in an adjusted gender analysis. A GLM model was used to assess 2-hour OGTT, fasting plasma glucose, difference between fasting plasma glucose and OGTT, HbA1c, HDL-cholesterol, LDL-cholesterol, and triglyceride in relation to current smoking, ex-smoking and never smoking. The effects were adjusted with covariates: gender, BMI, age, alcohol usage, educational level and ethnicity.

The OGTT results was lower for the group smoking (-10.1 [-13.2; -7.1], p < 0.001), and no effect was observed from ex-smoking (-2.7 [-5.7; 0.8], p = 0.08). Fasting glucose was not different for smokers (-0.2 [-1.6; 1.2], p = 0.80) or ex-smokers (0.1 [-1.3; 1.5], p = 0.90). For smokers', triglycerides (1.2 [1.1; 1.3], p < 0.001), LDL-cholesterol (7.7 [6.0; 9.3], p < 0.001) were increased and HDL-cholesterol was decreased (-2.1 [-2.8; -1.5], p < 0.001).

Although this study is cross-sectional and cannot, by the same nature of the design, prove a cause-effect relationship, the present results indicate that cigarette smoking may be associated with factors that are adversely related to the metabolic syndrome. But the evidence from our results are not unanimous pointing in the same direction as 2-hour OGTT measurements are considerably lower in participants smoking.