Colorectal cancer is one of the most common cancer types. Although the diet is of huge importance, the understanding of minerals and their interactions and preventative effect is limited. Earlier studies have shown that calcium and selenium have protective roles. It also looks as if having more selenium in the blood can improve the effect of calcium. This was demonstrated in a new Polish study that is published in BMC Nutrition. The scientists point out that there is widespread selenium deficiency in Europe and that supplementation may be needed.
Colorectal cancer is a collective name for cancer in the colon, rectum, and appendix. Although health authorities have introduced different types of screening procedures and various treatments, colorectal cancer is at the top of the list of cancer-related mortality. It is believed that diet and lifestyle account for around 70 percent of the cases. The risk is increased by consuming processed meats such as bacon, sausages, and cold cuts that have been cured, smoked, or had preservatives such as nitrite added to them for improved taste or shelf life.
Lack of exercise, overweight, excessive alcohol consumption, and ageing are some of the other factors that increase your risk. Lack of nutrients also plays a role, and science is particularly focused on selenium and calcium.
- Every year, 5,000 Danes are diagnosed with colorectal cancer
- Most patients are older than 50 years of age, and the risk of dying of the disease goes up with increasing age
- Diet and lifestyle play a crucial role
Selenium’s anti-cancer mechanisms
Selenium is a trace element that supports a host of different selenoproteins and their essential functions. We get selenium from offal, meat, eggs, and seafood. The selenium content in wheat and other crops is determined by the selenium content in the soil. In Europe and many other parts of the world, the farmland is selenium-depleted and that is why selenium deficiency is so widespread. Scientists are aware of this problem and it has their attention, as selenium has the following anti-cancer mechanisms:
- Affects gene activities, including Bcl-2
- Bcl-2 controls programmed cell death (apoptosis), a mechanism that helps abnormal and worn-out cells self-destruct
- Supports powerful antioxidants such as GPX that neutralizes potentially harmful free radicals
- Boosts the immune defense
- Dials down interleukin-2 and harmful inflammatory processes
- Helps to activate thyroid hormones
- Neutralizes the harmful effect of environmental toxins such as mercury
Several studies and meta-analyses have shown that selenium protects against colorectal cancer. Back in 1996, the American cancer researcher, Larry C. Clark, documented that daily supplementation with 200 micrograms of selenium yeast could lower the risk of colorectal by nearly 60 percent.
In 2017, scientists at the University College Dublin conducted a large selenium study where they looked at data from the so-called EPIC study. In this study, around half a million people had given blood samples and provided information about their diet and lifestyle. The scientists found that having more selenium in the blood was related to a significantly lower risk of developing colorectal cancer. The study suggests that a higher selenium intake may be relevant for most Europeans, simply because the average European selenium intake is below the optimal level.
There are conflicting results, however, as some studies have failed to demonstrate a statistically significant link between selenium intake and the risk of getting colorectal cancer. According to the authors of the new Polish study, this may be down to different dietary and lifestyle factors and different analytical methods.
The Polish scientists therefore wanted to look closer at calcium intake to see if this could possibly influence the effect of selenium. Apparently, dietary calcium is involved in the protection of the intestinal epithelium that serves as a gut barrier with a number of physiological functions. More precisely, calcium protects the epithelial cells through its effect on the synthesis of calcium-phosphate bile. Because selenium has other anti-cancer mechanisms that are related to the antioxidant defense, immune defense, and apoptosis, the scientists wanted to study them closer in relation to their ability to prevent colorectal cancer.
Optimal selenium levels offer the highest level of protection
The scientists looked at the diets of 683 patients diagnosed with colorectal cancer and 759 hospitalized patients with other diseases. They found an inverse relation between selenium intake and colorectal cancer risk. The cancer risk decreased by 30 percent in patients that got 60-80 micrograms of selenium every day. In patients who consumed more than 80 micrograms daily, the cancer risk decreased by as much as 60 percent.
The scientists also observed that low calcium intake impaired the effect of selenium and its anti-cancer effect. On the other hand, a higher calcium intake did not seem to have much effect on selenium and its ability to prevent cancer.
The researchers therefore suggest increasing the intake of selenium and calcium among people who don’t get enough of these two minerals.
This study supports earlier studies, and it appears that selenium’s protective effect on colorectal cancer peaks at intake doses of around 81-145 micrograms daily. There is no evidence to suggest an increased level of protection if you consume more than that. The European Food Safety Authority (EFSA) has established a safe upper intake level for selenium at 300 micrograms daily. The Polish study is published in BMC Nutrition.
How to compensate for low selenium intake and poor supplement quality
The official selenium recommendation in Denmark is around 55 micrograms daily. According to the new study, however, this is not enough to provide optimal protection against colorectal cancer. In fact, if you double or triple your selenium intake it may help reduce the risk of colorectal cancer and other cancer forms.
The best source of selenium for supplementation is selenium yeast that contains a variety of different organic selenium types, just like you get by eating a balanced diet with many different selenium sources. Interestingly, the so-called SELECT study where the study participants only got one type of selenium (selenomethionine) failed to demonstrate a protective effect on cancer. The selenium used for research is therefore of vital importance.
Malgorzata Augustyniak & Aleksander Galas. Calcium intake may explain the reduction of colorectal cancer odds by dietary selenium – a case control-study in Poland. BMC Nutrition. 2022
Clark LC et al: Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. JAMA: 1997.
Klein EA et al. Vitamin E and the risk of prostate cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2011.
Lutz Shomburg. Dietary Selenium and Human Health. Nutrients 2017
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