Plasma surfactant protein D levels and the relation to body mass index in a chinese population. 
Surfactant protein D (SP-D) is a member of the collectin family and is an important component of the pulmonary innate host defence.  The protein has a widespread distribution in the human body and is present in multiple epithelia, in endothelium and in blood.  Various studies have looked at the relationship between serum SP-D levels and pulmonary inflammatory diseases.  The SP-D distribution has been most thoroughly described in European populations and appears with a broad range of serum values highly influenced by genetic factors.  In the present study, we investigated the plasma SP-D distribution in a Chinese population from the Tai An region comprising 268 individuals.  We found that (i) plasma SP-D in the Chinese population was distributed with a median value of 380.2 ng/ml (324.9; 418.7) and a range from 79.4 to 3965.3 ng/ml, (ii) significantly higher plasma SP-D in men than in women, and no significant effect of age, and (iii) a significant inverse association between serum SP-D and body mass index (BMI) (P = 0.012).  The data indicate that racial differences in SP-D expression exist as the median plasma SP-D in the Chinese population was approximately two times lower than the median serum SP-D previously measured in a Danish population using the same immuno-assay.  The inverse association between serum SP-D and BMI found in the Chinese population indicates that serum SP-D is related to obesity in similar ways in Chinese and Danes.