['Mitochondrial DNA 5178 cytosine/adenosine (Mt5178 C/A) polymorphism is associated with longevity in the Japanese. The purpose of this study is to investigate whether Mt5178 C/A polymorphism modifies the effects of habitual smoking or habitual drinking on serum non-high-density lipoprotein (non-HDL) cholesterol levels in middle-aged Japanese men.', 'A total of 394 male subjects (age 53.9\u2009±\u20097.9 years; mean\u2009±\u2009SD) were selected from among individuals visiting the hospital for regular medical check-ups. After Mt5178 C/A genotyping, a cross-sectional study assessing the joint effects of Mt5178 C/A polymorphism and cigarette smoking or alcohol drinking on serum non-HDL cholesterol levels was conducted. High levels of serum non-HDL cholesterol were defined as serum non-HDL cholesterol levels ≥160 mg/dl or ≥190 mg/dl.', 'For men with Mt5178A, cigarette smoking may increase serum non-HDL cholesterol levels (P for trend\u2009<\u20090.001), as well as the risk of high levels of non-HDL cholesterol (serum non-HDL cholesterol levels ≥160 mg/dl, P for trend\u2009<\u20090.001; serum non-HDL cholesterol levels ≥190 mg/dl, P for trend\u2009=\u20090.004). On the other hand, for men with Mt5178C, after adjusting for age and body mass index, alcohol consumption may decrease serum non-HDL cholesterol levels (P for trend\u2009=\u20090.043) and the risk of high levels of non-HDL cholesterol (serum non-HDL cholesterol level ≥160 mg/dl, P for trend\u2009=\u20090.005).'] Is difference in effects of cigarette smoking or alcohol consumption on serum non-high-density lipoprotein cholesterol levels related to mitochondrial DNA 5178 C/A polymorphism in middle-aged Japanese men : a cross-sectional study?