Original articleDietary iron and vitamins in association with mortality
Introduction
Iron is an essential element for our body, since it participates in a wide variety of metabolic processes, including digestion of food, oxygen transport, and electron transport [1,2]. Iron is obtained mainly from dietary sources, which exists in the form of heme or non-heme iron [3,4].
Previous studies indicated that disorders of iron metabolism are among the most common diseases of diabetes, cardiovascular, pancreatic and colon cancer, and etc [[5], [6], [7], [8]]. However, results on the association of dietary iron with mortality were inconsistent. Dietary total iron was associated with risk of all-cause and cancer mortality in Belgian smoking man and Chinese adults, but no or significant association was found for cardiovascular disease (CVD) mortality in these two populations, respectively [9,10]. Some studies reported that higher dietary heme iron was related to higher risk of all-cause, CVD, and cancer mortality [[11], [12], [13], [14]], but others found no significant association [15]. Dietary non-heme iron was related to CVD mortality in Iowa postmenopausal women [12] whereas not in a Japan Collaborative Cohort (JACC) study [16]. Until now, limited data are available on dietary total/heme/non-heme iron with all-cause/CVD/cancer mortality in the same general population.
In addition, dietary intakes of vitamin A, B2, B6, C, E, and folic acid were known to affect the absorption or oxidation of iron in our body [[17], [18], [19], [20]]. To date, a total of three investigations were additionally adjusted for one or some of vitamin A, C, E, and folic acid in assessing the association of dietary total and heme iron with CVD mortality and the results were not changed in multivariable models [[12], [13], [14]]. Until now, no data on non-heme iron or mortality from all-cause or caner was reported. In addition, Hoydonck et al. developed a dietary oxidative balance score of vitamin C, β-Carotene and total iron intakes, which was observed to be positively associated with mortality risk from all-cause and cancer but not CVD in male smokers [9]. As we all know, vitamins do not be eaten isolated. Instead, they were eaten with combinations. To our knowledge, evidence on holistic effect of dietary vitamins or its interactive effect with iron on mortality is limited.
We therefore evaluated the association of dietary iron (total, heme, and non-heme), holistic intakes of vitamin A, B2, B6, C, E, and folic acid, and their interaction with mortality from all-cause, CVD and cancer in National Health and Nutrition Examination Survey (NHANES, 2003–2015).
Section snippets
Study population
The NHANES was a biannual, representative health survey of the United States population using highly stratified, multistage probability designs [21]. The survey is unique in that it combines interviews and physical examinations. The interview includes demographic, socioeconomic, dietary, and health-related questions [22]. The present investigation includes 3 two-year cycles (2003–2004, 2005–2006, and 2007–2008). We limited study sample to adults who were aged older than 18 years, were not
Characteristics of participants
During a median follow-up of 9.3 years, 2154 participants died. These deaths included 479 from all CVD and 466 from all cancers.
Compared with participants with iron intake smaller than median, participants with iron intake larger than median were significantly younger, tended to be males and current alcohol users, with higher prevalence of ever told had NCDs, higher dietary intakes of total energy, total, heme and non-heme iron, calcium, copper, fiber, vitamin A, B2, B6, C, E, folic acid and
Discussion
In this nationally representative sample of US adults, we observed that higher dietary heme iron was associated with higher CVD mortality while higher holistic intakes of vitamin A, B2, B6, C, E, and folic acid was associated with lower all-cause mortality. Results from interactive analysis suggest that higher holistic dietary vitamins combined with lower heme iron were associated with lower risk of all-cause and CVD mortality. Higher dietary vitamins combined with higher total/non-heme iron
Funding sources
This work was supported by grants from the National Natural Science Foundation of China (No. 82073536 and 81573134). The funding sponsors had no role in study design, data collection, statistical analysis and result interpretation, the writing of the report, and the decision to submit for publication.
Author's contributions
The authors’ responsibilities were as follows: XW: created the analytic design, analyzed the data, prepared the manuscript, and had primary responsibility for final content; WW and JG: created the analytic design, and interpreted the results; SH, LW, NL, YZ, TH, RS, YL, and CS: interpreted the results, and critically reviewed the manuscript. All authors read and approved the final manuscript.
Conflict of interest
The authors declare that they have no conflict of interests.
Acknowledgements
We thank the investigators, the staff, and the participants of the National Health and Nutrition Examination Survey for their valuable contribution. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
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These two authors made equal contribution to this work.