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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 DR and plasma vitamin C for Females.
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Figure 6: Correlation between dietary vitamin C measured by DR and plasma vitamin C for Females.

Mentions: We found 10 studies with 25 correlation coefficients, which measured vitamin C using dietary methods such as 24 hr DR or diet diary and biomarker. Again, some studies reported more than one correlation coefficient. Eleven correlations out of 25 were reported for "both" genders together. A meta-analysis on these studies indicates a positive correlation between DR or diet diary and biomarker with r = 0.46 (95%CI: 0.41, 0.52, see Figure 5). This analysis indicates homogeneity among groups (χ2 = 4.63, df = 2, p = 0.099) and that correlations within the crude group are not homogeneous (χ2 = 77.38, df = 7, p < 0.001). There were only two correlation coefficients in the supplement-excluded group. Next, we performed the same meta-analysis for males and females, separately. There was no heterogeneity observed among subgroups (see Figure 6 and Figure 7). The assumption of homogeneity within subgroups was not assessable because there was only one correlation coefficient within energy adjusted and supplement excluded groups. The estimated correlation coefficient was 0.44 (95% CI: 0.34, 0.55) for females and 0.36 (95% CI: 0.24, 0.48) for males. In our search we found only two studies which reported the correlation of dietary intake and plasma vitamin C for smokers (r = 0.60, 95% CI: 0.50, 0.70) and one study reported the correlation when adjusted for smoking (r = 0.36, 95% CI: 0.17, 0.55).


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 DR and plasma vitamin C for Females.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Correlation between dietary vitamin C measured by DR and plasma vitamin C for Females.
Mentions: We found 10 studies with 25 correlation coefficients, which measured vitamin C using dietary methods such as 24 hr DR or diet diary and biomarker. Again, some studies reported more than one correlation coefficient. Eleven correlations out of 25 were reported for "both" genders together. A meta-analysis on these studies indicates a positive correlation between DR or diet diary and biomarker with r = 0.46 (95%CI: 0.41, 0.52, see Figure 5). This analysis indicates homogeneity among groups (χ2 = 4.63, df = 2, p = 0.099) and that correlations within the crude group are not homogeneous (χ2 = 77.38, df = 7, p < 0.001). There were only two correlation coefficients in the supplement-excluded group. Next, we performed the same meta-analysis for males and females, separately. There was no heterogeneity observed among subgroups (see Figure 6 and Figure 7). The assumption of homogeneity within subgroups was not assessable because there was only one correlation coefficient within energy adjusted and supplement excluded groups. The estimated correlation coefficient was 0.44 (95% CI: 0.34, 0.55) for females and 0.36 (95% CI: 0.24, 0.48) for males. In our search we found only two studies which reported the correlation of dietary intake and plasma vitamin C for smokers (r = 0.60, 95% CI: 0.50, 0.70) and one study reported the correlation when adjusted for smoking (r = 0.36, 95% CI: 0.17, 0.55).

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