Does Selenium Reduce Cancer Risk? [Conflicting Research]

Selenium is an essential mineral that has been recognized for helping to protect cells from oxidative damage that can lead to cancer.

Preliminary clinical research on selenium and cancer suggests chemopreventive and anticancer effects. Some epidemeliogical data suggests that higher intake of this micronutrient can reduce cancer risk, but more research is needed to determine how effective it is.

According to the National Institutes of Health (NIH), selenium “appears to increase cancer cell death by causing apoptosis and by reducing the formation of ROS” (reactive oxygen species).

Although some scientific evidence suggests that selenium consumption may “produce anticarcinogenic effects in the body” and “reduce the risk of certain cancers”, the FDA states that the evidence to date is limited and not yet conclusive.

Selenium

Essential Mineral

Anti-Oxidant

Immunity

Thyroid Function

How It Works:

• Cofactor for antioxidant enzymes
• Supports thyroid function & metabolism
• Promotes immune function & fertility

Dosage:

Up to 400 mcg per day

Safety:

Rated Likely Safe at Appropriate Dosages

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Selenium and Cancer

Selenium (Se) is a trace chemical element with Atomic Number 34 on the Periodic Table of Elements.

In the human body, it plays a critical role in enzymes involved in defending cells against free radical molecules. It also has a role in recharging antioxidants such as Vitamin E.

According to a 2016 research review from Germany, “Selenium may modulate a broad spectrum of key biological processes, including the cellular response to oxidative stress, redox signalling, cellular differentiation, the immune response, and protein folding.” [1]

Selenium intake greater than the recommended dietary allowance (RDA) has been found to reduce risk factors related to cancer development and progression.

In certain parts of China, risk of esophageal and gastric cancer was reduced by half through supplementation with this trace mineral. It has also been shown to reduce growth rate of certain tumors, decrease lung and liver cancer, and inhibit the growth of colon polyps.

Selenium is the base constituent of various selenoproteins, including the glutathione peroxidases, which have important physiological roles related to immune function and more.

Researchers have discovered that humans have 25 selenoprotein genes while rodents have only 24. The anticancer effects of selenium differ substantially in relation to the specific selenoproteins at work. [2]

According to the National Cancer Institute, “Our knowledge about the roles of several selenoproteins in cancer is rapidly developing from different approaches that include biochemical, genetic and animal studies.”

Results from various studies have yielded “strong evidence” concerning the ways that different selenoproteins affect cancer, as well their involvement in other health benefits. In mice models, selenoproteins have shown a “direct role” in preventing both prostate and colon cancer. [2]

There seems to be a dual nature of selenium, selenoproteins and selenocompounds in cancer. While multiple studies suggest that selenoproteins prevent cancer, some research suggests that tumor formation (tumorigenesis) may be inhibited by low selenium levels.

It seems that selenium can help to prevent certain types of cancer. However, once a tumor is malignant, this mineral may promote its progression. The complex relationship between selenium and cancer is not yet clear.

Selenium and Cancer Prevention

Multiple population-based studies have suggested that people with high levels of selenium have less chances of developing cancer. This means that higher dietary intake of this mineral is correlated with lower risk of cancer.

However, there is a difference between correlation and causation. More studies are needed to understand if increasing your consumption of this mineral can cause cancer risk to decrease or if it is a mere statistical association.

Some studies have examined the causative effects of selenium supplementation on reducing cancer risk. These studies use a placebo group to determine differences between the control group and the treatment group.

The Nutritional Prevention of Cancer study randomized more than 1300 high-risk dermatology patients into either a placebo group or a treatment group that received 200 mcg/day doses of selenized yeast.

Results show that selenium supplementation reduced the risks of lung, colon, prostate and total cancer with clinical significance. However, the risk for nonmelanoma skin cancer increased. [3]

In a small human study, 424 subjects were randomized into either a placebo group, a group that received 200 mcg/day Selenium doses, or a group that received 400 mcg/day doses.

Results showed a 25% decreased risk for cancer in the 200 mcg/day group. The group that received 400 mcg/day doses showed no effects on total cancer incidence. [4]

More research is needed to understand if, and to what degree selenium may prevent or reduce different types of cancer in humans. Selenium is not currently an FDA-approved drug for preventing cancer.

Anti-Cancer Properties and Mechanisms

In addition to potentially preventing the development of cancerous cells, researchers are also interested in understanding whether this supplement can treat cancers that have already developed.

Recent research suggests multiple anticancer properties of selenium. However, the specific mechanisms of action are not yet well understood.

A 2015 in vitro study from China Medical University examined selenium’s effects on apoptosis (normal cell death), growth inhibition and oxidative stress in human breast cancer cells. The following results were reported for cells treated with selenized yeast:

• Time-and-dose-dependent inhibition of cell growth;
• Increased antioxidant enzyme activities;
• Increased growth-inhibition responses;
• Increased early apoptosis;

This study suggests that selenium supplementation can “increase oxidative stress, and stimulate growth inhibitory effects and apoptosis induction in breast cancer cell lines, but does not affect non-tumorigenic cells.” [5]

In vitro laboratory studies are the very first step in evaluating clinical efficacy. Additional research in controlled animal and human studies will be needed to determine efficacy of selenium for treating cancer.

Selenium and Prostate Cancer

According to the Natural Medicines Comprehensive Database (NMCD), there is some research that suggests selenium could reduce prostate cancer risk, but other research appears to show the opposite.

The prostate gland seems to accumulate selenium, helping to protect itself from oxidative stress and damage to DNA and to increase apoptosis in cancerous cells.

Populational evidence associates low blood selenium levels with increased probabilities for developing prostate cancer. High selenium levels in the blood are associated with a slower rate of progression in cancerous prostate tumors.

In one large-scale clinical trial, men were given 200 mcg of selenium per day for 4.5 years. During the study period, there was a 63% relative risk reduction in developing prostate cancer compared to a group taking a placebo.

However, in the SU.VI.MAX study a combination of 100 mcg selenium with Vitamin E, Vitamin C, beta-carotene and zinc did not have a significant effect on prostate cancer. Another large placebo-controlled trial known as the SELECT trial involved men using 200 mcg/day for 5.5 years and also did not see a significant reduction in prostate cancer risk.

More research is required to better understand selenium’s apparent anticancer mechanisms. According to NMCD, “Overall, the best evidence shows that taking selenium does not significantly reduce the risk of prostate cancer in otherwise healthy men.”

Selenium Safety & Side Effects

When used orally at appropriate dosages, selenium is rated Likely Safe. However, there are dangers associated with taking amounts greater than the tolerable upper intake level (UL) of 400 mcg/day. There are also concerns linked to long-term use of this supplement.

NMCD states that there are certain adverse effects associated with both selenium deficiency and selenium toxicity. It is known that selenium deficiency is rare, even in regions where soil content is very low.

In most cases, adequate intake of selenium rich foods provides enough of this mineral to avoid any deficiency symptoms. Some of the best natural food sources are Brazil nuts, green leafy vegetables, seafood, bread, eggs and pasta.

The upper tolerable daily levels (UL) for selenium is at 400 mcg/day. Selenium toxicity may result from chronic or acute intake above this level. The US RDA for selenium is 55 mcg/day for healthy people over 14 years of age.

In certain parts of the world, such as Europe, selenium-enriched foods such as milk products have been introduced to the market to improve selenium status in the blood. Europeans are known to have lower levels of this mineral in their diet than North Americans.

If you get too much selenium in your diet, or take excessive amounts of a supplement, you may develop toxicity symptoms. Some of these include hair loss, nausea, diarrhea, irritability, skin lesions and nervous system abnormalities.

Long-term use of this product at excess dosages could increase the risk of developing type 2 diabetes and insulin resistance.

Selenium can also interact with certain health conditions, diseases, lab tests, foods, drugs and herbal supplements. You should seek medical advice about taking selenium and how to reduce your risk for cancer before increasing your intake of this mineral.

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