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American Journal of Clinical Nutrition, Vol. 86, No. 5, 1548-1549, November 2007
© 2007 American Society for Nutrition

LETTER TO THE EDITOR

Reply to D Sluik et al

Ahmad Esmaillzadeh and Leila Azadbakht

Department of Nutrition
School of Health
Isfahan University of Medical Sciences
PO Box 81745
Isfahan
Iran
E-mail: esmaillzadeh{at}hlth.mui.ac.ir

Dear Sir:

In our recent article (1), entitled "Fruit and vegetables intakes, C-reactive protein, and the metabolic syndrome," we concluded that a higher intake of fruit and vegetables is associated with a lower risk of the metabolic syndrome; part of this association may be mediated through C-reactive protein concentrations. These findings support current dietary recommendations to increase the intake of fruit and vegetables as a primary preventive measure against cardiovascular disease.

First, we thank Sluik et al for their interest in our article. They claimed in their letter that the corrected odds ratios we derived from logistic regression models may yield inaccurate estimates of the association between fruit and vegetable intakes and the metabolic syndrome. We obtained adjusted prevalence odds ratios from logistic regression models, but because the prevalence of the metabolic syndrome in our study population was high (>10%), we used the formula suggested by Zhang and Yu (2) to correct these odds ratios. Although previous investigations have shown that the prevalence ratio is preferred over the prevalence odds ratio for evaluating associations in cross-sectional data (3, 4), inaccurate estimates with the use of the prevalence odds ratio would result when the odds ratio is >2.5 or <0.5 (2). This is not the case in our article, as shown in our Table 4. Furthermore, we corrected the simple odds ratios obtained from logistic regression, which can further attenuate the prevalence odds ratio toward the value of the prevalence ratio. However, both the prevalence odds ratio and the prevalence ratio would maintain statistical significance (if a significant association really exists) (5) and choosing either one would not affect the association between fruit and vegetable intakes and the metabolic syndrome.

ACKNOWLEDGMENTS

None of the authors declared any personal or financial conflicts of interest.

REFERENCES

  1. Esmaillzadeh A, Kimiagar M, Mehrabi Y, Azadbakht L, Hu FB, Willett WC. Fruit and vegetable intakes, C-reactive protein, and the metabolic syndrome Am J Clin Nutr 2006;84:1489–97.[Abstract/Free Full Text]
  2. Zhang J, Yu KF. What's the relative risk? A method of correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280:1690–1.[Abstract/Free Full Text]
  3. Thompson ML, Myers JE, Kriebel D. Prevalence odds ratio or prevalence ratio in the analysis of cross sectional data: what is to be done? Occup Environ Med 1998;55:272–7.[Abstract/Free Full Text]
  4. Skov T, Deddens J, Petersen MR, Endahl L. Prevalence proportion ratios: estimation and hypothesis testing. Int J Epidemiol 1998;27:91–5.[Abstract/Free Full Text]
  5. Schiaffino A, Rodríguez M, Pasarín MI, Regidor E, Borrell C, Fernández E. Odds ratio or prevalence ratio? Their use in cross-sectional studies. Gac Sanit 2003;17:70–4.




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