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Published online October 1, 2007
Diabetes Care 31:285-286, 2008
DOI: 10.2337/dc07-0921
© 2008 by the American Diabetes Association
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Epidemiology/Health Services Research
Original Research

Body Iron Stores and Dietary Iron Intake in Relation to Diabetes in Adults in North China

De Chun Luan, MD, MPH, Hui Li, MD, Sui Jing Li, MD, Zhuo Zhao, MD, Xin Li, MD and Zhong Mei Liu, MD

From the Institute for Nutrition and Food Safety, Liaoning Provincial Center for Disease Control and Prevention, Shenyang, China

Address correspondence and reprint requests to Suijing Li, Institute for Nutrition and Food Safety, Liaoning Provincial Center for Disease Control and Prevention, 42-1 Ji Xian St., Shenyang 110005, China. E-mail: lisuijing88{at}sohu.com


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 RESULTS--
 CONCLUSIONS--
 References
 
OBJECTIVE—To evaluate the association between body iron stores, dietary iron intake, and risk of diabetes in northern China.

RESEARCH DESIGN AND METHODS—The data of a cross-sectional household survey in 2002 in Liaoning Province in northern China was used. The final sample in our study contained 2,997 subjects aged ≥18 years. Fasting plasma glucose and serum ferritin were measured. Dietary information was collected by 3-day food records.

RESULTS—Serum ferritin was associated with elevated risk of diabetes even adjusted for age, sex, nondietary factors, and dietary factors. No association among total iron intake, nonheme iron intake, and diabetes risk was found. However, higher heme iron intake was significantly associated with elevated risk of diabetes after adjusting for known factors.

CONCLUSIONS—In Chinese, associations among higher serum ferritin level, higher heme iron intake, and elevated risk of diabetes were found.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
RESULTS--
 CONCLUSIONS--
 References
 
The 2002 China National Nutrition and Health Survey is a nationally representative cross-sectional survey (1). Data presented in this article are based on subsamples from Liaoning Province in northern China. A multistep cluster-sampling method was used for subject selection (1). Sampling involved a total of 12,059 subjects aged 1–96 years, representing the population of Liaoning Province. Written consent was obtained from all participants. In the study presented here, only adults, who were selected for dietary assessments and blood sample collection, aged ≥18 years old were involved.

Trained interviewers went to the subjects’ homes to collect information on food intake using the 24-h dietary recall method for 3 consecutive days. Total iron, heme iron, nonheme iron, and other nutrient intakes were calculated using data of dietary intake in conjunction with the China Food Composition Table (2).

A health status questionnaire and a 1-year physical activity questionnaire were adopted to collect the information of health behavior and lifestyle. An individual who had smoked daily for at least 6 months during his/her life was defined as a smoker. A drinker was defined as one who drank an alcohol product at least once a week. Sedentary time was total time spent watching TV, reading, playing electric games, and operating a computer during leisure time. Family history of diabetes was defined as the presence of known family members with diabetes in any of three generations.

At the study site, all anthropometric measurements were made by trained investigators using standard techniques. Plasma glucose level was measured with a spectrophotometer within 4 h after a fasting blood sample was obtained. Serum ferritin was analyzed in the laboratory of the National Institute for Nutrition and Food Safety (Beijing, China) using a commercially available radioimmunoassay kit (Beijing North Institute of Biological Technology). Plasma total cholesterol, triacylglycerols, and HDL cholesterol were measured enzymatically with an Hitachi 7060 7180 auto-analyzer (Hitachi, Tokyo, Japan) (1). Diabetes was defined as fasting plasma glucose ≥7.0 mmol/l.

All statistical analyses were performed with SAS software (SAS Institute, Cary, NC). We divided all subjects into four quartiles according to serum ferritin level, total iron intake, heme iron intake, or nonheme iron intake. Logistic regression was used to analyze association among serum ferritin, total iron intake, heme iron intake, nonheme iron intake, and risk of diabetes. Tests of linear trend across quartiles were conducted by assigning the median value for each quartile and fitting this continuous variable in the model. Subjects who were known to have diabetes and had fasting plasma glucose <7.0 mmol/l were excluded from this study.


   RESULTS—
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS--
CONCLUSIONS--
 References
 
In total, 1,618 women and 1,379 men were involved in this study. Mean ± SD age was 46.5 ± 14.7 years. Prevalence of diabetes was 4.9%. Mean serum ferritin level, total iron intake, heme iron intake, and nonheme iron intake were 105.4 ± 87.5 µg/l and 19.6 ± 8.8, 2.7 ± 3.3, and 16.1 ± 8.4 mg/l, respectively.

Serum ferritin was associated with elevated risk of diabetes even adjusted for age, sex, nondietary factors, and dietary factors (Table 1). No association among total iron intake, nonheme iron intake, and diabetes risk was found after adjusting for known factors. However, heme iron intake was positively associated with risk of diabetes adjusted for known factors (Table 1).


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  		Table 1— Odds ratios (95% CIs) for diabetes by quartiles of serum ferritin level and heme iron intake in subjects

 
In model building, it was found that abnormal blood lipid, family history of diabetes, central obesity, and dietary intake of fat mainly confounded the association between iron status and diabetes risk and might replace the effects of iron (Table 1). For example, if blood lipid was not adjusted, total iron intake was significantly associated with elevated risk of diabetes in women (odds ratio 1.00 [referent], 1.29 [95% CI 0.62–2.67], 2.04 [0.93–4.51], and 2.71 [1.12–6.56] for quartiles 1–4, respectively; Ptrend = 0.0192), consistent with the recent study in southern China (3). However, nonheme iron intake remained unassociated with diabetes risk.


   CONCLUSIONS—
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS--
 CONCLUSIONS--
References
 
Increasing evidence suggests that high body iron stores (4–5) and only heme iron in diet (6–8) are associated with elevated risk of diabetes in Western countries. However, Chinese dietary pattern is unique in that it consists of more plant food and less animal food. A recent study in southern China (3) reported that serum ferritin and total iron intake were significantly associated with elevated diabetes risk. But without data analysis, they concluded that nonheme iron intake may play a role in association between iron status and diabetes in the Chinese context. To confirm these results, we conducted this study.

Though racial background of the Chinese population differs from that in West-ern countries, the positive association between serum ferritin (a biomarker of body iron store) and diabetes risk was also found in our study. As to dietary iron, we only found that heme iron intake was associated with elevated diabetes risk, consistent with several studies in Western countries (6–8). However, there was little difference between our results and those of the study in southern China (3). We could have had a similar association between total iron and diabetes risk if we did not adjust for blood lipid. But blood lipid, family history of diabetes, waist circumference, and dietary intake of fat were main confounders that should be adjusted. We only found that heme iron plays a role in association between total iron and diabetes; nonheme iron intake didn't affect the association.

Our study confirmed earlier findings (3) that body iron associates with glucose homeostasis in the Chinese population and identified intake of heme iron as a potential causal factor. However, a cohort study is needed to confirm the causal relation.


   Acknowledgments
 
The 2002 China National Nutrition and Health Survey was supported by the Ministry of Health and Ministry of Science and Technology, Beijing, China (2001 DEA30035 and 2003DIA6N008).


   Footnotes
 
Published ahead of print at http://care.diabetesjournals.org on 27 September 2007. DOI: 10.2337/dc07-0921.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received for publication May 14, 2007. Accepted for publication September 24, 2007.


   References
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS--
 CONCLUSIONS--
 References
 

  1. Li LM, Rao KQ, Kong LZ, Yao CH, Xiang HD, Zhai FY, Ma GS, Yang XG: A description on the Chinese national nutrition and health survey in 2002. Zhonghua Liu Xing Bing Xue Za Zhi 26: 474–484, 2005 [article in Chinese]
  2. Yang Y: China Food Composition Table. Pan X, Wang G, Eds. Beijing, China, Beijing Medical University Press, 2002
  3. Shi Z, Hu X, Yuan B, Pan X, Meyer HE, Holmboe-Ottesen G: Association between serum ferritin, hemoglobin, iron intake, and diabetes in adults in Jiangsu, China. Diabetes Care 29: 1878–1883, 2006[Abstract/Free Full Text]
  4. Jiang R, Manson JE, Meigs JB, Ma J, Rifai N, Hu FB: Body iron stores in relation to risk of type 2 diabetes in apparently healthy women. JAMA 291: 711–717, 2004[Abstract/Free Full Text]
  5. Ford ES, Cogswell ME: Diabetes and serum ferritin concentration among U.S. adults. Diabetes Care 22: 1978–1983, 1999[Abstract/Free Full Text]
  6. Jiang R, Ma J, Ascherio A, Stampfer MJ, Willett WC, Hu FB: Dietary iron intake and blood donations in relation to risk of type 2 diabetes in men: a prospective cohort study. Am J Clin Nutr 79: 70–75, 2004[Abstract/Free Full Text]
  7. Lee DH, Folsom AR, Jacobs DR Jr: Dietary iron intake and type 2 diabetes incidence in postmenopausal women: the Iowa Women's Health Study. Diabetologia 47: 185–194, 2004[Medline]
  8. Rajpathak S, Ma J, Manson J, Willett WC, Hu FB: Iron intake and the risk of type 2 diabetes in women: a prospective cohort study. Diabetes Care 29: 1370–1376, 2006[Abstract/Free Full Text]

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This Article
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