Reply to A Astrup

USC/Norris Comprehensive Cancer Center University of Southern California Keck School of Medicine Los Angeles, CA 90033-0800 E-mail: jyuan{at}hsc.usc.edu

Dear Sir:

Astrup raised the question of whether body mass index (BMI) is a determinant of plasma total homocysteine (tHcy) concentrations in Singapore Chinese. He also wondered about the possibility of BMI as a confounder of the associations of tHcy with age and sex.

BMI (in kg/m²) was not a predictor of plasma homocysteine in Singapore Chinese of either sex (Table 1). This population had a relatively low BMI (22.8) compared with Western populations (eg, a BMI of 26 in US white men and women) (1). As reported in Saw et al (2), we found the following factors to be independent predictors of plasma tHcy in Singapore Chinese: age; sex; plasma folate, vitamin B-12, and vitamin B-6 concentrations; and methylenetetrahydrofolate reductase (MTHFR) genotype. Adjustment for the above factors did not materially change the null BMI-tHcy relationship. The statistically significant, positive associations between age and tHcy concentrations in both men and women (P for trend < 0.001 for both) remained when BMI was adjusted for. Similarly, the BMI- and age-adjusted geometric means of tHcy between the sexes remained significant (P < 0.001). We also noted that adjustment for BMI did not materially alter the significant associations of plasma folate, vitamin B-12, and vitamin B-6 and MTHFR genotype with tHcy.

View this table:
TABLE 1. Geometric mean plasma total homocysteine (tHcy) concentrations by BMI in men and women in the Singapore Chinese Health Study  

REFERENCES

1. Kuczmarski RJ, Flegal KM, Campbell SM, Johnson CL. Increasing prevalence of overweight among US adults. The National Health and Nutrition Examination Surveys, 1960 to 1991. JAMA 1994; 272:205–11.
2. Saw S-M, Yuan J-M, Ong C-N, et al. Genetic, dietary, and other lifestyle determinants of plasma homocysteine concentrations in middle-aged and older Chinese men and women in Singapore. Am J Clin Nutr 2001;73:232–9.