Selenium’s anti-cancer properties in selenium-enriched foods and relevant supplements

Cancer has become one of the leading causes of death, with rates going up every year. The diet plays a major role and there is a lot of focus on selenium as an anti-cancer agent – both in the form of selenium-enriched functional foods and selenium supplements. Around one billion people worldwide are believed to lack selenium. According to a review article that is published in Foods, however, taking a daily supplement of 100-200 micrograms of selenium yeast can prevent deficiency and reduce some of the most common cancers by fifty percent.

In 2020 alone, there were nearly 10 million cancer deaths globally. According to Global Cancer Statistics (GLOBOCAN), the number of cancer-related deaths will exceed 28 million in 2040. The massive growth in cancer diseases is ascribed to environmental and dietary factors which means, that around half of all cancers could be prevented by means of diet and lifestyle. Over the past years, there has been increasing focus on the trace element selenium that has a number of anti-cancer mechanisms, at least if you do not have enough selenium in the body.

Widespread selenium deficiency and increased need

The selenium content in the agricultural soil worldwide varies a lot and so does the selenium content in the diet. In Eastern Europe, for example, the diet provides between 10-30 micrograms of selenium per day, while the selenium intake in Venezuela is around 200-350 micrograms daily. Because the selenium intake in Europe and large parts of the Middle East, China, Asia, and Africa is low, selenium deficiency has turned into a global problem.
The official daily recommendation for selenium is around 50-70 micrograms daily, but studies suggest that we need 100-200 micrograms per day to properly prevent genetic damage and the development of cancer growths. On the other hand, it is important not to get too much selenium. According to EFSA (the European Food Safety Authority), there is a safe upper intake level of 300 micrograms per day.

Studies of selenium and cancer

In the review article, the authors refer to the NCP (Nutritional Prevention of Cancer) study, which is the first double-blind, randomized, placebo-controlled study of selenium and cancer. Professor Larry C. Clark and his team of scientists who carried out the trial showed that daily supplementation with 200 micrograms of selenium yeast could lower the risk of three of the most common cancer types by 48-63 percent and lower cancer mortality by around 50 percent.
The authors also refer to the SELECT study (Selenium and Vitamin E Cancer Prevention Trial) that demonstrated that supplementation with selenomethionine and synthetic vitamin E did not have the same positive effect.
The different outcome of these two trials can be attributed to several factors. First of all, the studies were conducted using different selenium sources. Secondly, a positive effect can not necessarily be expected if the study is carried out on people who are not selenium-deficient in the first place.
Over the past decades, multiple studies have shown that sufficient selenium intake from dietary sources or supplements can prevent a number of different cancer forms. It is important to take into account that it takes years for cancer to develop, so it is important to get plenty of selenium throughout life, especially in old age where the cancer risk goes up.

Functional foods and selenium yeast with many different selenium species

Functional foods are foods with certain health benefits that are linked to their content of specific vitamins and minerals. Functional foods are often designed to have specific effects. The authors mention several foods that are rich in selenium such as Brazil nuts, garlic, broccoli, Brussels sprouts, various types of cabbage, fish, mussels, egg yolk, liver, and offal.
Similarly, they mention studies where Brazil nut consumption has been shown to raise blood levels of selenium and lower the risk of bowel cancer. They also mention studies of humans and animals that show that consumption of selenium-enriched broccoli, broccoli sprouts, and garlic can help prevent different types of cancer. One must also look at the fact that these foods contain many other nutrients that may have a synergistic effect.
Selenium yeast that is found in supplement form contains a variety of different selenium species, which is similar to the variety of selenium types that you get by eating a balanced diet with different sources. Manufacturing methods vary, however, so it is normally a good idea to choose selenium yeast with documented bioavailability to make sure that the nutrient reaches the cells.
In Finland, selenium-enrichment of agricultural fertilizers has been mandatory since 1984. This simple measure has affected the entire food chain in Finland, and the Finnish population, as the only one in Europe, gets at least 100 micrograms of selenium daily from the daily diet.

Selenium content in different foods (micrograms pr. 100 grams of food)

Brazil nuts 2-20
Garlic 0.15
Broccoli 0.13
Brussel sprouts 0.25
Fish 0.4 – 4.3
Meat (muscle meat) 0.3
Egg yolk 0.12 – 0.42

Selenium’s anti-cancer mechanisms

Selenium supports between 25 and 30 different selenoproteins that are involved in complicated metabolic processes. The selenoproteins help regulate cellular energy turnover, metabolism, fertility, and many other functions. Although science has not yet mapped out all the different anti-cancer mechanisms of selenium, the authors do mention that selenium:

• Has antioxidant properties that protect the cells against oxidative stress and DNA damage caused by free radicals
• Supports the immune defense and helps it destroy cancer cells and combat carcinogens
• Helps regulate inflammation that is the common thread in most chronic illnesses
• Controls gene expression and cellular activity
• Counteracts angiogenesis (the formation of new blood vessels) that are involved with the growth of cancer
• Counteracts tumor cell invasion
• Regulates apoptosis (programmed self-destruction of cells)

References:

Malgorzata Dobrzynska el al. Natural Sources of Selenium as Functional Food Products for Chemoprevention. Foods 2023

Jing Huang et al. Selenium Status and Its Antioxidant Role in metabolic Diseases. Oxidative Medicine and Cellular Longevity. 2022

Aparna Shreenath. Selenium Deficiency. StatPearls. May 6, 2019

Bronislaw A et al. Selenium (Se) Intake and Plasma Se Concentration in Low Soil-Se Countries. Scientific Journal of Food Science & Nutrition 2018