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Is plasma vitamin C an appropriate biomarker of vitamin C intake? A systematic review and meta-analysis.

Dehghan M, Akhtar-Danesh N, McMillan CR, Thabane L - Nutr J (2007)

Bottom Line: A total of 26 studies were selected and their results were combined using meta-analytic techniques with random-effect model approach.An overall correlation of 0.39 was found when using the weight record method.Adjusting for energy intake improved the observed correlation for FFQ from 0.31 to 0.41.

View Article: PubMed Central - HTML - PubMed

Affiliation: Population Health Research Institute, School of Medicine, McMaster University, Hamilton, Canada. mahshid@ccc.mcmaster.ca

ABSTRACT

Background: As the primary source of dietary vitamin C is fruit and to some extent vegetables, the plasma level of vitamin C has been considered a good surrogate or predictor of vitamin C intake by fruit and vegetable consumption. The purpose of this systematic review was to investigate the relationship between dietary vitamin C intakes measured by different dietary methods and plasma levels of vitamin C.

Method: We searched the literature up to May 2006 through the OVID interface: MEDLINE (from 1960) and EMBASE (from 1988). We also reviewed the reference lists in the articles, reviews, and textbooks retrieved. A total of 26 studies were selected and their results were combined using meta-analytic techniques with random-effect model approach.

Results: The overall result of this study showed a positive correlation coefficient between Food Frequency Questionnaire (FFQ) and biomarker (r = 0.35 for "both" genders, 0.39 for females, and 0.46 for males). Also the correlation between Dietary Recalls (DR)/diary and biomarker was 0.46 for "both" genders, 0.44 for females, and 0.36 for males. An overall correlation of 0.39 was found when using the weight record method. Adjusting for energy intake improved the observed correlation for FFQ from 0.31 to 0.41. In addition, we compared the correlation for smokers and non-smokers for both genders (FFQ: for non-smoker r = 0.45, adjusted for smoking r = 0.33).

Conclusion: Our findings show that FFQ and DR/diary have a moderate relationship with plasma vitamin C. The correlation may be affected/influenced by the presence of external factors such as vitamin bioavailability, absorption condition, stress and food processing and storage time, or by error in reporting vitamin C intake.

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Correlation between dietary vitamin C measured by FFQ and plasma vitamin C for "both" gender.
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Figure 2: Correlation between dietary vitamin C measured by FFQ and plasma vitamin C for "both" gender.

Mentions: We found 18 studies with 47 correlation coefficients between FFQ and the biomarker. Some studies reported more than one correlation coefficient for different genders, time-points, or adjusted and unadjusted correlation coefficients based on energy intake, supplement use, and other factors. Twenty correlation coefficients out of these 47 were reported for "both" genders together not for males and females separately. Some studies reported Pearson and some Spearman correlation coefficients. The overall meta-analysis for these 20 correlations resulted in a positive correlation coefficient between FFQ and biomarker (r = 0.35; 95%CI: 0.29, 0.40, see Figure 2). This analysis also indicated heterogeneity among correlation coefficients across studies (χ2 = 34.02, df = 19, p = 0.018). The subgroup meta-analysis for "both" genders showed that correlation coefficients for crude assessment of vitamin C in FFQs were heterogeneous (χ2 = 24.28, df = 12, p = 0.019); but the correlation coefficients within the two other sub-groups of energy adjusted and supplement excluded were homogenous (see Figure 2). The higher correlations are seen among studies that reported energy adjusted correlations for vitamin C (r = 0.41).


Is plasma vitamin C an appropriate biomarker of vitamin C intake? A systematic review and meta-analysis.

Dehghan M, Akhtar-Danesh N, McMillan CR, Thabane L - Nutr J (2007)

Correlation between dietary vitamin C measured by FFQ and plasma vitamin C for "both" gender.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2200644&req=5

Figure 2: Correlation between dietary vitamin C measured by FFQ and plasma vitamin C for "both" gender.
Mentions: We found 18 studies with 47 correlation coefficients between FFQ and the biomarker. Some studies reported more than one correlation coefficient for different genders, time-points, or adjusted and unadjusted correlation coefficients based on energy intake, supplement use, and other factors. Twenty correlation coefficients out of these 47 were reported for "both" genders together not for males and females separately. Some studies reported Pearson and some Spearman correlation coefficients. The overall meta-analysis for these 20 correlations resulted in a positive correlation coefficient between FFQ and biomarker (r = 0.35; 95%CI: 0.29, 0.40, see Figure 2). This analysis also indicated heterogeneity among correlation coefficients across studies (χ2 = 34.02, df = 19, p = 0.018). The subgroup meta-analysis for "both" genders showed that correlation coefficients for crude assessment of vitamin C in FFQs were heterogeneous (χ2 = 24.28, df = 12, p = 0.019); but the correlation coefficients within the two other sub-groups of energy adjusted and supplement excluded were homogenous (see Figure 2). The higher correlations are seen among studies that reported energy adjusted correlations for vitamin C (r = 0.41).

Bottom Line: A total of 26 studies were selected and their results were combined using meta-analytic techniques with random-effect model approach.An overall correlation of 0.39 was found when using the weight record method.Adjusting for energy intake improved the observed correlation for FFQ from 0.31 to 0.41.

View Article: PubMed Central - HTML - PubMed

Affiliation: Population Health Research Institute, School of Medicine, McMaster University, Hamilton, Canada. mahshid@ccc.mcmaster.ca

ABSTRACT

Background: As the primary source of dietary vitamin C is fruit and to some extent vegetables, the plasma level of vitamin C has been considered a good surrogate or predictor of vitamin C intake by fruit and vegetable consumption. The purpose of this systematic review was to investigate the relationship between dietary vitamin C intakes measured by different dietary methods and plasma levels of vitamin C.

Method: We searched the literature up to May 2006 through the OVID interface: MEDLINE (from 1960) and EMBASE (from 1988). We also reviewed the reference lists in the articles, reviews, and textbooks retrieved. A total of 26 studies were selected and their results were combined using meta-analytic techniques with random-effect model approach.

Results: The overall result of this study showed a positive correlation coefficient between Food Frequency Questionnaire (FFQ) and biomarker (r = 0.35 for "both" genders, 0.39 for females, and 0.46 for males). Also the correlation between Dietary Recalls (DR)/diary and biomarker was 0.46 for "both" genders, 0.44 for females, and 0.36 for males. An overall correlation of 0.39 was found when using the weight record method. Adjusting for energy intake improved the observed correlation for FFQ from 0.31 to 0.41. In addition, we compared the correlation for smokers and non-smokers for both genders (FFQ: for non-smoker r = 0.45, adjusted for smoking r = 0.33).

Conclusion: Our findings show that FFQ and DR/diary have a moderate relationship with plasma vitamin C. The correlation may be affected/influenced by the presence of external factors such as vitamin bioavailability, absorption condition, stress and food processing and storage time, or by error in reporting vitamin C intake.

Show MeSH