In a community-based rural Chinese twin cohort, we examined the distribution of plasma homocysteine levels across the lifespan and explored potential socio-demographic and clinical determinants of homocysteine. Using a co-twin analysis, we also estimated heritability of homocysteine, a measure of the relative contribution of environmental and genetic factors to homocysteine levels. This report includes 1117 subjects (657 male and 460 female twins; 556 twin pairs) free from diabetes, and 10-66 years of age. Plasma homocysteine levels were obtained by high performance liquid chromatography (HPLC) for all subjects. The socio-demographic (alcohol habit, smoking status, education and occupation) and clinical risk factors (triglycerides, HDL-C, systolic blood pressure, diastolic blood pressure, waist circumference, fasting glucose, and BMI) were also obtained for all subjects. We found that the distribution pattern for homocysteine varied by age and gender. Levels were higher for males than for females in each age group; and the degree of gender difference in homocysteine levels increased from early age all the way to age 30-40 years then began to decrease. The level for males kept increasing until age 30-40 years then began to decrease, while females showed a different trend. Among all of the potential risk factors, only blood pressure showed a strong association with plasma homocysteine levels. Genetic factors could explain 68.8% of the variance in plasma homocysteine levels for female adults. For male adults, only 35.5% of the variance in outcomes could be explained by genetic factors, suggesting that environmental factors may play an important role in regulating homocysteine levels among males.
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