Dietary iron intake and risk of non-fatal acute myocardial infarction

Triad role of hepcidin, ferroportin, and Nrf2 in cardiac iron metabolism: From health to disease

Iron is an essential trace element required for several vital physiological and developmental processes, including erythropoiesis, bone, and neuronal development. Iron metabolism and oxygen homeostasis are interlinked to perform a vital role in the functionality of the heart. The metabolic machinery of the heart utilizes almost 90 % of oxygen through the electron transport chain. To handle this tremendous level of oxygen, the iron metabolism in the heart is utmost crucial. Iron availability to the heart is therefore tightly regulated by (i) the hepcidin/ferroportin axis, which controls dietary iron absorption, storage, and recycling, and (ii) iron regulatory proteins 1 and 2 (IRP1/2) via hypoxia inducible factor 1 (HIF1) pathway. Despite iron being vital to the heart, recent investigations have demonstrated that iron imbalance is a common manifestation in conditions of heart failure (HF), since free iron readily transforms between Fe²⁺ and Fe³⁺via the Fenton reaction, leading to reactive oxygen species (ROS) production and oxidative damage. Therefore, to combat iron-mediated oxidative stress, targeting Nrf2/ARE antioxidant signaling is rational. The involvement of Nrf2 in regulating several genes engaged in heme synthesis, iron storage, and iron export is beginning to be uncovered. Consequently, it is possible that Nrf2/hepcidin/ferroportin might act as an epicenter connecting iron metabolism to redox alterations. However, the mechanism bridging the two remains obscure. In this review, we tried to summarize the contemporary insight of how cardiomyocytes regulate intracellular iron levels and discussed the mechanisms linking cardiac dysfunction with iron imbalance. Further, we emphasized the impact of Nrf2 on the interplay between systemic/cardiac iron control in the context of heart disease, particularly in myocardial ischemia and HF.

Dietary inflammatory index and acute myocardial infarction in a large Italian case-control study

Background

Diet and inflammation have been implicated to play a role in the incidence of acute myocardial infarction (AMI).

Methods

In this Italian case-control study conducted between 1995 and 2003, we explored the association between the dietary inflammatory index (DIITM) and AMI. Cases were 760 patients, below age 79 years, with a first episode of nonfatal AMI and controls were 682 patients admitted to hospital for acute conditions unrelated to diet. The DII was computed based on dietary intake assessed using a reproducible and validated 78-item food frequency questionnaire. Odds ratios (OR) were estimated through logistic regression models adjusting for age, sex, total energy intake, tobacco, body mass index, hypertension, hyperlipidemia and other recognized confounding factors.

Results

Higher DII scores (i.e., indicating a more pro-inflammatory diet) were associated with increased likelihood of AMI when expressed both as continuous (ORcontinuous=1.14, 95% confidence interval, CI:1.05, 1.24; one-unit increase in DII score corresponding to ≈9% of the range of DII) and as quartiles (ORQuartile4vs1= 1.60, 95%, CI 1.06, 2.41; P-trend = 0.02). Stratified analyses produced slightly stronger associations between DII and AMI among women, ≥60 years, never smokers, subjects with history of hypertension and subjects with no family history of AMI, however, in the absence of heterogeneity across strata.

Conclusion

A pro-inflammatory diet as indicated by higher DII scores is associated with increased likelihood of AMI.

Association of dietary iron restriction with left ventricular remodeling after myocardial infarction in mice

Several epidemiologic studies have reported that body iron status and dietary iron intake are related to an increased risk of acute myocardial infarction (MI). However, it is completely unknown whether dietary iron reduction impacts the development of left ventricular (LV) remodeling after MI. Here, we investigate the effect of dietary iron restriction on the development of LV remodeling after MI in an experimental model. MI was induced in C57BL/6 J mice (9-11 weeks of age) by the permanent ligation of the left anterior descending coronary artery (LAD). At 2 weeks after LAD ligation, mice were randomly divided into two groups and were given a normal diet or an iron-restricted diet for 4 weeks. Sham operation without LAD ligation was also performed as controls. MI mice exhibited increased LV dilatation and impaired LV systolic function that was associated with cardiomyocyte hypertrophy and interstitial fibrosis in the remote area, as compared with the controls at 6 weeks after MI. In contrast, dietary iron restriction attenuated LV dilatation and impaired LV systolic function coupled to cardiomyocyte hypertrophy and interstitial fibrosis in the remote area. Importantly, cardiac expression of cellular iron transport proteins, transferrin receptor 1 and divalent metal transporter 1 was increased in the remote area of MI mice compared with the controls. Dietary iron restriction attenuated the development of LV remodeling after MI in mice. Cellular iron transport might play a role in the pathophysiological mechanism of LV remodeling after MI.

Dietary intake of heme iron and risk of cardiovascular disease: a dose-response meta-analysis of prospective cohort studies

BACKGROUND AND AIMS

Iron is thought to play a fundamentally important role in the development of cardiovascular disease (CVD). This meta-analysis was performed to investigate the dose-response association between dietary intake of iron (including heme and non-heme iron) and the risk of CVD.

METHODS AND RESULTS

We performed a search of the PubMed and Embase databases for prospective cohort studies of the association between dietary iron intake and CVD risk. Thirteen articles comprising 252,164 participants and 15,040 CVD cases were eligible for inclusion. Heme iron intake was associated significantly with increased risk of cardiovascular disease, and the pooled relative risk (RR) for each 1 mg/day increment was 1.07 (95% confidence interval: 1.01 to 1.14, I² = 59.7%). We also found evidence of a curvilinear association (P < 0.05 for non-linearity). In contrast, we found no association between CVD risk and dietary non-heme (0.98, 0.96 to 1.01, I² = 15.8%) or total iron (1.00, 0.94 to 1.06, I² = 30.4%). Subgroup analyses revealed that the association between heme iron intake and CVD risk was stronger among non-fatal cases (1.19, 1.07-1.33) and American patients (1.31, 1.11-1.56).

CONCLUSIONS

Higher dietary intake of heme iron is associated with an increased risk of cardiovascular disease, whereas no association was found between CVD and non-heme iron intake or total iron intake. These findings may have important public health implications with respect to preventing cardiovascular disease.

Is heme iron intake associated with risk of coronary heart disease? A meta-analysis of prospective studies

PURPOSE

Heme iron may contribute to the development of atherosclerosis by catalyzing production of hydroxyl-free radicals and promoting low-density lipoprotein oxidation. However, epidemiologic findings regarding the association between heme iron intake and risk of coronary heart disease (CHD) are inconsistent. We aimed to investigate the association by carrying out a meta-analysis of prospective studies.

METHODS

Relevant studies were identified by using PubMed and EMBASE databases between January 1966 and April 2013 and also by manually reviewing the reference lists of retrieved publications. Summary relative risks (RRs) with corresponding 95% confidence intervals (CIs) were computed using a random-effects model.

RESULTS

Six prospective studies, which contained a total of 131,553 participants and 2,459 CHD cases, met the inclusion criteria. Combined results indicated that participants with higher heme iron intake had a 31% increased risk of CHD, compared with those with lower intake (RR = 1.31, 95% CI 1.04-1.67), with significant heterogeneity (P(heterogeneity) = 0.05, I(2) = 55.0%). Excluding the only study from Japan (limiting to Western studies) yielded a RR of 1.46 (95% CI 1.21-1.76), with no study heterogeneity (P(heterogeneity) = 0.44, I(2) = 0.0%). The dose-response RR of CHD for an increase in heme iron intake of 1 mg/day was 1.27 (95% CI 1.10-1.47), with low heterogeneity (P (heterogeneity) = 0.25, I (2) = 25.8%). We observed no significant publication bias.

CONCLUSIONS

This meta-analysis suggests that heme iron intake was associated with an increased risk of CHD.

Associations of dietary iron intake with mortality from cardiovascular disease: the JACC study

Background

We investigated the relationship between dietary iron intake and mortality from cardiovascular disease (CVD) in a population-based sample of Japanese adults.

Methods

The study cohort consisted of 58 615 healthy Japanese (23 083 men and 35 532 women), aged between 40 and 79 years, who had no history of stroke, coronary heart disease (CHD), or cancer at baseline. Dietary iron intake was assessed at baseline by a validated food frequency questionnaire administered between 1988 and 1990 as part of the Japan Collaborative Cohort (JACC) Study.

Results

We documented 2690 (1343 men and 1347 women) deaths from CVD: 1227 (607 men and 620 women) deaths from total stroke, 651 from ischemic stroke (355 men and 296 women), 459 (196 men and 263 women) from hemorrhagic stroke, and 557 (311 men and 246 women) from CHD. Dietary intake of total iron was positively associated with mortality from total and ischemic stroke and total CVD in men. The multivariable hazard ratio for the highest versus the lowest quintile of total iron intake was 1.43 (95% CI, 1.02–2.00; P for trend = 0.009) for total stroke and 1.27 (1.01–1.58; 0.023) for total CVD in men. Dietary total iron intake was not associated with mortality from other endpoints in men, and was not associated with any endpoints in women.

Conclusions

Dietary intake of total iron was positively associated with mortality from stroke and total CVD in Japanese men.

Relation of iron and red meat intake to blood pressure: cross sectional epidemiological study

OBJECTIVE

To investigate associations of dietary iron (total, haem, and non-haem), supplemental iron, and red meat with blood pressure.

DESIGN

Cross sectional epidemiological study.

SETTING

17 population samples from Japan, China, the United Kingdom, and the United States participating in the international collaborative study on macro-/micronutrients and blood pressure (INTERMAP).

PARTICIPANTS

4680 adults aged 40-59.

MAIN OUTCOME MEASURE

Average of eight blood pressure readings.

RESULTS

In multiple linear regression analyses dietary total iron and non-haem iron were consistently inversely associated with blood pressure. With adjustment for potential non-dietary and dietary confounders, dietary total iron intake higher by 4.20 mg/4.2 MJ (2 SD) was associated with -1.39 mm Hg (P<0.01) lower systolic blood pressure. Dietary non-haem iron intake higher by 4.13 mg/4.2 MJ (2 SD) was associated with -1.45 mm Hg (P<0.001) lower systolic blood pressure. Differences were smaller for diastolic blood pressure. In most models haem iron intake from food was positively, non-significantly associated with blood pressure. Iron intake from combined diet and supplements yielded smaller associations than dietary iron alone. Red meat intake was directly associated with blood pressure; 102.6 g/24 h (2 SD) higher intake was associated with 1.25 mm Hg higher systolic blood pressure. Associations between red meat and blood pressure persisted after adjustment for multiple confounders.

CONCLUSION

Non-haem iron has a possible role in the prevention and control of adverse blood pressure levels. An unfavourable effect of red meat on blood pressure was observed. These results need confirmation including in prospective studies, clinical trials, and from experimental evidence on possible mechanisms.