The omission of eligible publications may bias the conclusions
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Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies
Liang Zhou
Department of Sports Physiology, Hunan University of Science and Technology, Xiangtan, Hunan, China
In the recent issue of BMJ, Wang et al. (1) used a meta-analysis to examine the association between fruit and vegetable intake and risk of total, cardiovascular, and cancer mortality. They found that intake of fruits and vegetables for one serving per day may slightly decrease the risk of all cause, cardiovascular, and cancer mortality.
However, they omitted a number of eligible publications that may bias the conclusions. For total mortality and intake of fruit and vegetable combined, they at least omitted one eligible publication (2). For total mortality and intake of fruit alone, at least three eligible publications (3-5) have been missed. In addition, they included two ineligible publications (6,7) and both studies investigated the association between fruit and juices in combination and risk of total mortality. Based on the recent findings (8,9), fruits and fruit juices have different effect on human health. For total mortality and intake of vegetable alone, also at least at least three eligible publications (3-5) have been omitted.
In conclusions, the omission of eligible studies and inclusion of ineligible ones might have biased their conclusions. The authors have reported publication bias for their meta-analysis and we guess the publication bias may be due to the omission of eligible publications.
References
1. Wang X, Ouyang Y, Liu J, Zhu M, Zhao G, Bao W, Hu FB. Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies. BMJ 2014;349:g4490.
2. Nechuta SJ, Shu XO, Li HL, Yang G, Xiang YB, Cai H, Chow WH, Ji B, Zhang X, Wen W, Gao YT, Zheng W. Combined impact of lifestyle-related factors on total and cause-specific mortality among Chinese women: prospective cohort study. PLoS Med. 2010 Sep 14;7. pii: e1000339.
3. Mann JI, Appleby PN, Key TJ, Thorogood M. Dietary determinants of ischaemic heart disease in health conscious individuals. Heart. 1997;78:450-5.
4. Ness AR, Maynard M, Frankel S, Smith GD, Frobisher C, Leary SD, Emmett PM, Gunnell D. Diet in childhood and adult cardiovascular and all cause mortality: The boyd orr cohort. Heart. 2005;91:894-8.
5. Lo YT, Chang YH, Wahlqvist ML, Huang HB, Lee MS. Spending on vegetable and fruit consumption could reduce all-cause mortality among older adults. Nutr J. 2012;11:113.
6. Sahyoun NR, Jacques PF, Russell RM. Carotenoids, vitamins C and E, and mortality in an elderly population. Am J Epidemiol. 1996;144:501-11.
7. Whiteman D, Muir J, Jones L, Murphy M, Key T. Dietary questions as determinants of mortality: the OXCHECK experience. Public Health Nutr. 1999;2:477-87.
8. Xi B, Li S, Liu Z, Tian H, Yin X, Huai P, Tang W, Zhou D, Steffen LM. Intake of fruit juice and incidence of type 2 diabetes: a systematic review and meta-analysis. PLoS One. 2014;9:e93471.
9. Li S, Miao S, Huang Y, Liu Z, Tian H, Yin X, Tang W, Steffen LM, Xi B. Fruit intake decreases risk of incident type 2 diabetes: an updated meta-analysis. Endocrine. 2014 Jul 30. [Epub ahead of print].
Competing interests:
No competing interests
10 August 2014
Liang Zhou
Teacher
Department of Sports Physiology, Hunan University of Science and Technology
Rapid Response:
Liang Zhou
Department of Sports Physiology, Hunan University of Science and Technology, Xiangtan, Hunan, China
In the recent issue of BMJ, Wang et al. (1) used a meta-analysis to examine the association between fruit and vegetable intake and risk of total, cardiovascular, and cancer mortality. They found that intake of fruits and vegetables for one serving per day may slightly decrease the risk of all cause, cardiovascular, and cancer mortality.
However, they omitted a number of eligible publications that may bias the conclusions. For total mortality and intake of fruit and vegetable combined, they at least omitted one eligible publication (2). For total mortality and intake of fruit alone, at least three eligible publications (3-5) have been missed. In addition, they included two ineligible publications (6,7) and both studies investigated the association between fruit and juices in combination and risk of total mortality. Based on the recent findings (8,9), fruits and fruit juices have different effect on human health. For total mortality and intake of vegetable alone, also at least at least three eligible publications (3-5) have been omitted.
In conclusions, the omission of eligible studies and inclusion of ineligible ones might have biased their conclusions. The authors have reported publication bias for their meta-analysis and we guess the publication bias may be due to the omission of eligible publications.
References
1. Wang X, Ouyang Y, Liu J, Zhu M, Zhao G, Bao W, Hu FB. Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies. BMJ 2014;349:g4490.
2. Nechuta SJ, Shu XO, Li HL, Yang G, Xiang YB, Cai H, Chow WH, Ji B, Zhang X, Wen W, Gao YT, Zheng W. Combined impact of lifestyle-related factors on total and cause-specific mortality among Chinese women: prospective cohort study. PLoS Med. 2010 Sep 14;7. pii: e1000339.
3. Mann JI, Appleby PN, Key TJ, Thorogood M. Dietary determinants of ischaemic heart disease in health conscious individuals. Heart. 1997;78:450-5.
4. Ness AR, Maynard M, Frankel S, Smith GD, Frobisher C, Leary SD, Emmett PM, Gunnell D. Diet in childhood and adult cardiovascular and all cause mortality: The boyd orr cohort. Heart. 2005;91:894-8.
5. Lo YT, Chang YH, Wahlqvist ML, Huang HB, Lee MS. Spending on vegetable and fruit consumption could reduce all-cause mortality among older adults. Nutr J. 2012;11:113.
6. Sahyoun NR, Jacques PF, Russell RM. Carotenoids, vitamins C and E, and mortality in an elderly population. Am J Epidemiol. 1996;144:501-11.
7. Whiteman D, Muir J, Jones L, Murphy M, Key T. Dietary questions as determinants of mortality: the OXCHECK experience. Public Health Nutr. 1999;2:477-87.
8. Xi B, Li S, Liu Z, Tian H, Yin X, Huai P, Tang W, Zhou D, Steffen LM. Intake of fruit juice and incidence of type 2 diabetes: a systematic review and meta-analysis. PLoS One. 2014;9:e93471.
9. Li S, Miao S, Huang Y, Liu Z, Tian H, Yin X, Tang W, Steffen LM, Xi B. Fruit intake decreases risk of incident type 2 diabetes: an updated meta-analysis. Endocrine. 2014 Jul 30. [Epub ahead of print].
Competing interests: No competing interests