This Nutrient May Lower Colon Cancer Risk

Colorectal cancer is one of the most common cancers worldwide. It ranks as the third most diagnosed cancer in men and the second in women, with nearly 2 million new cases reported in 2020. Specifically in Korea, colorectal cancer rates have been rising quickly, increasing by about 2.6% each year since 2019.

While it is true that there are some factors that are out of our control when it comes to colon cancer risk, other factors, including smoking, drinking excess alcohol, lack of exercise and dietary choices, can be controlled. Recently, scientists have suggested that eating red and processed meats (like bacon) might increase the risk of colon cancer. One possible reason for that connection is the heme iron these foods contain. Heme iron is a type of iron found in animal-based foods, which is more easily absorbed by the body than non-heme iron found in plant-based sources. While there are benefits to leaning on heme iron, some researchers suggest they may contribute to harmful reactions in the body that increase cancer risk.

However, research on the link between heme iron and colon cancer has shown mixed results, with some studies suggesting a higher risk in Western countries and others showing little to no risk, especially in Asian countries like Japan. These findings highlight that the relationship may vary based on factors like gender, location and eating habits.

To explore how different types of iron in the diet, such as iron from animal sources (heme iron) and plant sources (non-heme iron), are linked to the risk of colorectal cancer in a large group of healthy Koreans, researchers conducted a study evaluating this population, and the results were published in Nutrients.

How Was the Study Conducted?

To evaluate the associations between total, heme, and non-heme iron intake and the risk of colorectal, colon, and rectal cancer in Koreans, researchers used data from The Korean Genome and Epidemiology Study’s Health Examinees cohort (KoGES HEXA), a long-term research project carried out in health centers and hospitals across Korea. 

At the beginning of the study, researchers assessed what the participants typically ate over the past year using detailed interviews and a food questionnaire. This questionnaire asked how often participants ate certain foods and how much they usually ate. The questionnaire included 106 common foods in the Korean diet. 

The researchers then calculated the iron content of these foods, measuring two types of dietary iron for each participant: heme iron, which comes from animal-based foods like meat and fish, and non-heme iron, found in plant-based foods and other sources. 

Cases of colorectal cancer in this study were identified using data from the Korea Central Cancer Registry, managed by the National Cancer Center of Korea. Additional data were collected about participants’ age, sex, smoking and drinking habits, education level, family history of colorectal cancer and any history of conditions like hypertension, diabetes or high cholesterol. Information on physical activity was also gathered through questionnaires, while height and weight were measured to calculate body mass index (BMI). 

With all of this information, analyses were conducted to determine potential links. In total, 109,908 people (37,697 men and 71,401 women) were tracked for an average of 9.1 years, and their information was used for this analysis. 

What Did the Study Find?

During the study, 608 new cases of colorectal cancer (CRC) were diagnosed (299 in men and 309 in women). Researchers found that people who consumed moderate amounts of iron daily had a noticeably lower risk of developing colorectal cancer compared to those who consumed the least amount of iron. For colon cancer specifically, moderate iron consumption also correlated to a lower risk. In this study, a moderate amount of iron was classified as 5.00–6.27 mg per day—that’s about as much as you’d get in a serving of our One-Pot Lentils & Rice with Spinach. (That’s just a fraction of your recommended daily value, which varies depending on age and sex.)

When it came to heme iron consumption, the researchers didn’t see a noticeable effect on the risk of developing colorectal or colon cancer. But for non-heme iron consumption, the researchers found that people in the group with moderate non-heme iron intake had a lower risk of colorectal cancer compared to those with the lowest consumption. 

Specifically, for those who consumed a moderate amount of non-heme iron: 

• their risk of CRC was reduced by 25%.
• their risk of colon cancer was reduced by 30%. 

For the men in the moderate non-heme group, the effects were even more significant. Men who consumed a moderate amount of non-heme iron had a 32% lower risk of CRC and a 44% lower risk of colon cancer. Additionally, as non-heme iron intake increased, there was a noticeable trend of lower colon cancer risk for both sexes. 

It’s interesting to note that the benefits of iron, particularly non-heme iron (plant-based iron), don’t increase steadily with higher consumption. Instead, the most protective effects were seen in a moderate intake range in this study. The researchers propose that this might be because iron consumption in Korea is generally quite low. 

To put things into perspective, the recommended daily amount of iron is 8 mg for adult men and women over 51, and 18 mg for adult women under 50. But for the lowest consumption group in this study, some participants were only getting between 1 and 5 mg of iron per day, which is far below the recommended amount.

The authors highlight that having too little iron has been linked to a higher risk of certain cancers, and this may be why strong benefits were not seen among those with the lowest intake of this nutrient. 

Like all studies, this one has some limitations to be aware of. This study is observational, and observational studies often face challenges with confounding variables, like overall diet. Another limitation is that the researchers only measured dietary habits at the start of the study, so any changes in eating patterns over time weren’t taken into account. The study also neglected to collect information about any iron supplements that participants may have been taking.

How Does this Apply to Real Life?

Hearing headlines linking eating red meat to cancer can be alarming. But this study underscores how understanding the nuanced results of studies can help make informed dietary choices without overhauling your eating habits entirely. 

For example, while these findings don’t conclusively link heme iron intake to colon cancer risk, it’s worth being mindful of your overall diet. Many Americans consume more meat than the recommended amounts, which could lead to overconsumption of heme iron along with other factors like saturated fats and calories that may contribute to health concerns. That doesn’t mean you need to cut out meat altogether—instead, focus on portion control and balancing your meals with plenty of plant-based foods, which are rich in other nutrients (like fiber—a nutrient that may be linked to a reduced risk of colorectal cancer).

Whenever you think about making a change to your eating habits, it’s crucial to consider your whole diet rather than just one nutrient. This study highlights that moderate, diversified consumption of both heme and non-heme iron might offer protective benefits, particularly in populations where overall iron intake tends to be lower. Incorporating iron-rich plant-based foods like lentils, spinach and tofu can support a well-rounded diet while offering additional advantages, such as dietary fiber and phytonutrients. 

Don’t overdo it with this mineral—too much may not be a good thing for your body. But by taking small, practical steps, you can build a diet that’s both enjoyable and supportive of your health goals.

The Bottom Line

A recent study in Nutrients sheds light on the nuanced relationship between iron intake and colorectal cancer (CRC) risk, particularly in a Korean population. The findings underscore the importance of balance, as moderate iron consumption, both heme and non-heme, was associated with a reduced risk of CRC and colon cancer. This research emphasizes that dietary habits, cultural context, and baseline nutrient consumption levels play a vital role in interpreting study results and shaping dietary recommendations. 

While the study highlights potential protective effects of moderate iron intake, it also reminds us of the dangers of both under- and over-consumption. These findings reinforce the value of a well-rounded diet that includes a mix of nutrient-dense foods, emphasizing plant-based sources of iron alongside moderate portions of animal-based options.