RESUMO
<p><b>OBJECTIVE</b>To describe the distribution of plasma folate concentrations and prevalence of folate deficiency in adults aged 35 to 64 years in some areas and different seasons in China.</p><p><b>METHODS</b>Study subjects were sampled from the representative rural and urban areas in the south and north of China aged 35 to 64 years totaling 2 545, and their plasma folate concentrations were determined and analyzed.</p><p><b>RESULTS</b>Plasma concentrations of folate in the southern population were significantly higher (16.9 nmol/L) than those in the north (8.3 nmol/L), and the prevalence of folate deficiency in the south (5.8%) was significantly lower than that in the north (37.1%). Plasma folate concentration varied with season either in the south or north. Plasma concentrations of folate were lower during the summer and the fall (15.0 nmol/L) than those during the winter and the spring (18.8 nmol/L) in the south, but without significant changes in the prevalence of folate deficiency in different seasons. However, the plasma folate concentrations were significantly higher during the summer and the fall (9.7 nmol/L) than those during the winter and the spring (7.1 nmol/L) in the north. And the prevalence of folate deficiency in the north was significantly higher in winter and spring (48.0%) than that in summer and fall (26.2%).</p><p><b>CONCLUSIONS</b>There existed significant difference in plasma folate concentrations in adults between varied geographic areas in China, which differed from their seasonal changes.</p>