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Written by: Ana Iturbides, Health Writer, Acupuncture Atlanta
Dae Jung Kim, MD, Pengcheng Xun, MD, PhD, Kiang Liu, PhD, Catherine Loria, PhD, Kuninobu Yokota, MD, PhD, David R. Jacobs, Jr., PhD, Ka He, MD, ScD
Certain foods and nutrients may be associated with the onset of diabetes. This particular study focuses on the effects of magnesium on the incidence of diabetes, as measured through systemic inflammation and insulin resistance. Magnesium is a mineral that is found in abundance in the body. It is essential for hundreds of biochemical processes, such as maintaining muscle and nerve function, steadying heart rhythm, supporting the immune system, and ensuring bone health (NIH). Prior studies have examined the effects of magnesium supplements on the risk of diabetes, but findings have been inconclusive. Kim and colleagues investigated the relationship between magnesium intake and the incidence of diabetes in a cohort of young American adults participating in the Coronary Artery Risk Development in Young Adults (CARDIA) study (Kim et al., 2604). The authors also examined the extent to which magnesium intake was associated with systemic inflammation markers. These included high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), fibrinogen, and the homeostasis model assessment of insulin resistance (HOMA-IR).
Research Design and Methods
The CARDIA study is an ongoing, multi-center, prospective cohort study that investigates the role of lifestyle and other factors in the development of risk factors for cardiovascular diseases among young adults (Kim et al., 2604). A prospective cohort study is a type of study design in epidemiology that follows two groups over time that are alike in many ways, except for one key characteristic. This type of study compares two groups for a particular outcome (National Cancer Institute). From this group, Kim and colleagues enforced various exclusion criteria. These criteria included the following:
· Participants who took anti-diabetic medication;
· Participants who did not participate in follow-up examinations for the CARDIA study;
· Participants who had missing data on magnesium, total energy intake, pregnancy during examination period, smoking status, alcohol consumption, physical activity, and waist circumference;
Kim and colleagues conducted their analysis on 4,497 participants after implementing exclusion criteria. They assessed magnesium intake primarily by collecting dietary data at baseline, examination year 7, and examination year 20 by using a validated CARDIA Diet History Questionnaire (Kim et al., 2605). This questionnaire included items that had to do with dietary supplement intake. The authors defined “magnesium intake” as the combination of dietary magnesium intake and magnesium supplementation.
A variety of covariates were also studied. Covariates are variables that may be predictive of the outcome being studied by investigators and included age, sex, ethnicity, alcohol consumption, waist circumference, diastolic fifth-phase blood pressure, and physical activity.
The inflammatory markers described in the introduction were measured in a variety of ways. Serum hs-CRP was measured at year 7, 15, and 20 using a nephelometry-based high throughput assay. IL-6 was analyzed at year 20 using a high-sensitivity enzyme-linked immunosorbant assay (Kim et al., 2605). CV and Fibrinogen were assessed at years 5, 7 and 20. Fasting plasma glucose and insulin levels were examined at baseline as well as years 7,10,15, and 20. Kim and colleagues determined the presence of diabetes if participants had one or more of the following:
· Fasting plasma glucose greater than or equal to 7.0 mmol/l during years 0,7,10,15, and 20;
· Non-fasting plasma glucose greater than or equal to 11.1 mmol/l during years 0,7,10,15, and 20;
· Postprandial 2-h plasma glucose greater than or equal to 11.1 mmol/l for years 10 and 20;
· AIC greater than or equal to 6.5% in year 20;
· Reported use of anti-diabetic medication;
The authors were not able to make a clear distinction between type I and type II diabetes due to the fact that participants were young and used insulin as treatment.
Statistical analysis consisted of the ANOVA, Kruskal-Wallace, and chi square tests. Initial analyses were adjusted for age, sex, ethnicity and study center. The authors tested for interaction between magnesium and covariates by adding terms in the models and conducting likelihood ratio tests.
The authors found that during the 20 year follow up, 330 incident cases of diabetes were identified. Magnesium intake was found to be inversely related to the incidence of diabetes. Statistical analyses show that the incidence of diabetes was 47% lower for participants in the highest quintile compared with that for those in the lowest quintile after adjusting for possible confounders (Kim et al., 2606). After adjusting for confounders, the inverse effects of magnesium intake on incidence of diabetes were most pronounced in women, overweight individuals, and those without a family history of diabetes. Additionally, a significant inverse association between magnesium intake and HOMA-IR was observed (Kim et al., 2607).
The authors found an inverse relationship between magnesium intake and incidence of diabetes. These results are generally consistent with many previous studies. The inverse relationship between magnesium intake and HOMA-IR was thought to be particularly interesting because it is suspected that this relationship may be due to the role that magnesium plays in improving insulin sensitivity. This suggests that low magnesium intake may adversely affect insulin sensitivity.
The authors claim that their study’s strengths include a long-term follow up period, a large sample size, and a sample that was well balanced regarding sex and ethnicity. Additionally, they examined a variety of inflammatory markers and used three separate measures to define diabetes. Lastly, the results of the study are consistent with findings for dietary magnesium intake, serum magnesium level, and consumption of whole grains. The authors also acknowledge several limitations to the study, including the possibility for confounding due to unmeasured factors, the inherent limitations posed by dietary questionnaires, and the lack of statistical control of all possible sources of systemic inflammation (Kim et al., 2608).
There is a possibility that magnesium intake may be beneficial in decreasing the risk for diabetes due to the mineral’s positive effects on systemic inflammation and insulin resistance. More large-scale studies are needed to strengthen causal inference for this potential benefit.
 Kim, Dae Jung, et al. “Magnesium Intake in Relation to Systemic Inflammation, Insulin Resistance, and the Incidence of Diabetes”. Diabetes Care 33(12); 2010; P. 2604-2610.
 National Cancer Institute, Dictionary of Cancer Terms. “Prospective Cohort Study”. http://www.cancer.gov/dictionary/?CdrID=286693.
 National Institutes of Health, Office of Dietary Supplements. “Magnesium”. http://ods.od.nih.gov/factsheets/magnesium/.
|This article was published on Thursday December 23, 2010.|