Findings from different studies suggested excess iron/heme iron intake to be a risk factor for cancers such as Breast Cancer and Pancreatic Cancer; however, total iron intake or non-heme iron intake may have a protective effect in colorectal and esophageal cancers. Based on the studies assessed in this blog, in cancers such as lung cancer and prostate cancer, no significant associations were found. More well-defined studies are needed to establish these findings. While the intake of the right amounts of iron is important for the proper functioning of our body, its excess intake may lead to side effects and can also be fatal for children. Hence, consult a doctor before taking dietary iron supplements.
Iron – The Essential Nutrient
Iron is an essential mineral which is vital for the proper functioning of hemoglobin, a protein that is required for transporting oxygen in the blood, and for the growth and development. Being an essential nutrient, iron needs to be obtained from our diet. It also plays an important role in various other processes such as creating serotonin, muscle functioning, energy production, gastrointestinal processes, regulation of body temperature, DNA synthesis and boosting the immune system.
Iron is stored mostly in the liver and bone-marrow as ferritin or hemosiderin. It may also be stored in spleen, duodenum and skeletal muscle.
Food Sources of Iron
Some of the examples of food sources of iron include:
- Red Meat
- Dried Fruits such as dried dates and apricots
- Soy bean
Types of Dietary Iron
Dietary iron is present in two forms:
- Heme iron
- Non-heme iron
Heme iron comprises approximately 55-70% of the total iron from animal products such as red meat, poultry and fish and has a greater efficiency of absorption.
Non-heme iron comprises the rest of the iron and the iron present in plant-based foods such as legumes and cereals, and iron supplements. It is difficult to absorb iron from plant based foods. Please note that using Vitamin C will help in absorbing Iron.
The iron deficiency, called anaemia, is a condition where lack of iron in the body results in a lesser number of healthy red blood cells which can carry oxygen to the tissues.
The recommended daily allowance of Iron varies with age and gender :
- 8.7mg a day for men over 18
- 14.8mg a day for women aged 19 to 50
- 8.7mg a day for women over 50
These amounts can be usually obtained from our diet.
Iron deficiency is the most common nutrient deficiency in the world. Hence, previously the focus related to dietary iron was more towards iron deficiency. However, in the recent past, researchers have also been exploring the impacts of excess iron in the body. In this blog, we will focus on some of the studies which assessed the association between iron and the risk of different types of cancers.
Association between Iron and Breast Cancer Risk
Serum and Tumor Tissue Iron and Breast Cancer Risk
A meta-analysis done by the researchers from the Golestan University of Medical Sciences, Ilam University of Medical Sciences, Shahid Beheshti University of Medical Sciences and Birjand University of Medical Sciences evaluated the association between iron and breast cancer risk. The analysis included 20 articles (involving 4,110 individuals with 1,624 breast cancer patients and 2,486 controls) which were published between 1984 and 2017 and obtained through literature search in PubMed, Scopus, Embase, Web of Science, and Cochrane Library. (Akram Sanagoo et al, Caspian J Intern Med., Winter 2020)
The analysis found a high risk of breast cancer with high iron concentration in the groups where iron was measured in breast tissues. However, they didn’t find any association between iron concentration and breast cancer risk in the groups where iron was measured in scalp hair.
Iron intake, body iron status, and Breast Cancer Risk
Researchers from the University of Toronto and Cancer Care Ontario, Canada carried out a meta-analysis to evaluate the associations between both iron intake and body iron status and breast cancer risk. 23 studies were included for the analysis post literature search in MEDLINE, EMBASE, CINAHL, and Scopus databases till December 2018. (Vicky C Chang et al, BMC Cancer., 2019)
They found that when compared to those with lowest heme iron intake, there was a 12% increase in breast cancer risk in those with highest heme iron intake. However, they didn’t find any significant association between dietary, supplemental or total iron intake and breast cancer risk. Further well-defined clinical studies are needed to better elucidate the association between iron and breast cancer risk.
Impact of Antioxidant Supplementation on the association between Dietary iron intake and Breast Cancer Risk
A study done by the researchers in France in 2016 evaluated the association between dietary iron intake and breast cancer risk, and its potential modulation by an antioxidant supplementation and lipid intake in 4646 women from the SU.VI.MAX trial. During a mean follow-up of 12.6 years, 188 breast cancer cases were reported. (Abou Diallo et al, Oncotarget., 2016)
The study found that dietary iron intake was associated with an increased breast cancer risk, especially in women who consumed more lipids, however, this association was found only for those who were not supplemented with antioxidants during the trial. The study concluded that breast cancer risk may have been increased by iron-induced lipid peroxidation.
NIH-AARP Diet and Health Study
In another analysis of dietary data from 193,742 postmenopausal women who were a part of the in the NIH-AARP Diet and Health Study, with 9,305 incident breast cancers identified (1995-2006), it was found that high heme iron intake was associated with an increased risk of breast cancer, overall and at all cancer stages. (Maki Inoue-Choi et al, Int J Cancer., 2016)
Association between Iron and Colorectal Cancer Risk
Iron Intake, Serum Iron Indices and Risk of Colorectal Adenomas
Researchers from the Zhejiang Provincial People’s Hospital and The First People’s Hospital of Fuyang District in China, evaluated the association between iron intake, serum iron indices and the risk of colorectal adenoma, using data from 10 articles, involving 3318 colorectal adenoma cases, obtained through literature search in MEDLINE and EMBASE until 31 March 2015. (H Cao et al, Eur J Cancer Care (Engl)., 2017)
The study found that an increased intake of heme iron is associated with significantly increased risk of colorectal adenoma, whereas intake of non-heme or supplemental iron reduced the risk of colorectal adenomas. Based on the limited data available, there were no associations between serum iron indices and colorectal adenoma risk.
Intakes of heme iron and zinc and colorectal cancer incidence
A study done by the researchers from the Shengjing Hospital of China Medical University in China evaluated the associations between intakes of heme iron and zinc and colorectal cancer incidence. Eight studies on heme iron intake and six studies on zinc intake were used for the analysis which were obtained through literature search in PubMed and EMBASE databases till December 2012. (Lei Qiao et al, Cancer Causes Control., 2013)
This meta-analysis found a significant increase in colorectal cancer risk with increased heme iron intake and a significant decrease in colorectal cancer risk with increased zinc intake.
Association between Iron and Esophageal Cancer Risk
Researchers from the Zhengzhou University and Zhejiang University School of Medicine in China did a systematic meta-analysis to evaluate the association between the intake of total iron and zinc and lower heme iron and the risk of Esophageal Cancer. Data for the analysis was obtained from 20 articles with 4855 cases from 1387482 participants, obtained from literature search in Embase, PubMed, and Web of Science databases through April 2018. (Jifei Ma e al, Nutr Res., 2018)
The study found that every 5 mg/day increase in total iron intake was associated with a 15% reduced risk of Esophageal Cancer. The risk reduction was found especially in Asian populations. Conversely, every 1 mg/day increase in heme iron intake was associated with a 21% increase in Esophageal Cancer risk.
Association between Iron and Pancreatic Cancer Risk
A study published in 2016 evaluated the association of meat intake, meat cooking methods and doneness and heme iron and mutagen intake with pancreatic cancer in the NIH-AARP Diet and Health Study cohort involving 322,846 participants of which 187,265 were men and 135,581 were women. After a mean follow-up of 9.2 years, 1,417 pancreatic cancer cases were reported. (Pulkit Taunk et al, Int J Cancer., 2016)
The study found that pancreatic cancer risk significantly increased with intake of total meat, red meat , high-temperature cooked meat, grilled/barbequed meat, well/very well done meat and heme iron from red meat. The researchers have suggested more well-defined studies to confirm their findings.
Association between Iron and Prostate Cancer Risk
In a study published by the researchers from the EpidStat Institutes in Michigan and Washington in the US, they evaluated the association between meat cooking methods, heme iron, and heterocyclic amine (HCA) intake and prostate cancer based on 26 publications from 19 different cohort studies. (Lauren C Bylsma et al, Nutr J., 2015)
Their analysis did not find any association between red meat or processed meat consumption and prostate cancer; however, they found a small increase in risk with processed meats consumption.
Association between Serum Iron Levels and Lung Cancer Risk
A study done by the researchers from the Zhejiang Rongjun Hospital, Zhejiang Cancer Hospital, Fujian Medical University Cancer Hospital and Lishui Hospital of Zhejiang University in China evaluated the association between serum iron levels and lung cancer risk. Data for the analysis was obtained from PubMed, WanFang, CNKI, and SinoMed databases till Mar 1, 2018. The study found that serum iron levels had no significant association with lung cancer risk. (Hua-Fei Chen et al, Cell Mol Biol (Noisy-le-grand)., 2018)
Use of Iron Supplements in the Management of Chemotherapy-induced Anemia in Cancer Patients
A study done by the Center for Evidence Based Medicine and Health Outcomes Research, University of South Florida, Tampa, Florida, USA evaluated the benefits and harms related to the use of iron supplements alongside Erythropoiesis-stimulating agents (ESAs), which are commonly used to treat chemotherapy-induced anemia (CIA), and Cochrane Database Syst iron alone compared with ESA alone in the management of CIA. (Rahul Mhaskar et al, Rev., 2016)
The study found that including iron supplements along with ESAs may lead to superior hematopoietic response, reduce the risk of Red Blood Cell transfusions, and improve haemoglobin levels.
These studies suggested varying effects of iron in different cancers. Excess iron was found to be a risk factor for cancers such as Breast Cancer and Pancreatic Cancer, possibly due to its pro-oxidant activity which can lead to oxidative DNA damage; however, total iron intake and non-heme iron intake, was found to have protective effects in colorectal and esophageal cancer. In cancers such as lung cancer and prostate cancer, no significant associations were reported. While the intake of the right amounts of iron is important for the proper functioning of our body, its excess intake via supplements may lead to side effects such as constipation and stomach pain and can also be fatal for children. Hence, consult a doctor before taking iron supplements. The required amounts of iron can be obtained from foods.
Cancer patients often have to deal with different chemotherapy side effects which affect their quality of life and look out for alternative therapies for cancer. Taking the right nutrition and supplements based on scientific considerations (avoiding guesswork and random selection) is the best natural remedy for cancer and treatment related side-effects.