Is Selenium safe?
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Is Selenium Safe? A Comprehensive Review
Selenium Safety in Cancer Prevention
Selenium and Lung Cancer Chemoprevention
Selenium has been investigated for its potential chemopreventive benefits in lung cancer. A randomized, double-blind, placebo-controlled trial evaluated selenium supplementation in patients with resected stage I non-small-cell lung cancer (NSCLC). The study found that selenium was safe but did not confer any significant benefit over placebo in preventing second primary tumors (SPTs)1. Additionally, a systematic review and meta-analysis indicated that selenium might reduce lung cancer risk in populations with lower baseline selenium status but could increase risk in those with higher selenium levels8.
Selenium Toxicity and Safe Upper Limits
Reassessment of Safe Upper Limits in Drinking Water
Recent epidemiologic studies suggest that the current safe upper limits for selenium in drinking water may need reassessment. Evidence indicates that human toxicity can occur at much lower levels than previously thought, particularly with inorganic selenium compounds like selenate found in drinking water. This has led to recommendations for reducing the upper limit to 1 µg/l to protect human health adequately2.
Selenium and Cardiovascular Risk
Selenium is essential for the activity of glutathione peroxidases and other selenoproteins, but its safety margin is narrow. While some studies suggest a moderate inverse relationship between selenium levels and coronary heart disease, others indicate that high selenium intake may increase the risk of diabetes and hypercholesterolemia. Therefore, the current evidence does not support selenium supplementation for cardiovascular prevention, especially in selenium-replete populations3.
Selenium in Daily Diet and Supplements
Nutritional Selenium and Health Risks
Selenium is a vital nutrient found in various foodstuffs, with high levels in meat, eggs, poultry, and seafood. While low selenium levels are associated with higher mortality risk and immune dysfunction, excessive selenium intake can lead to toxicity. The benefits of selenium supplements for preventing cardiovascular diseases, hepatopathies, or cancers remain ambiguous, and their indiscriminate use could increase toxicity risk4.
Forms of Selenium in Supplements
Selenium supplements come in different chemical forms, with selenomethionine being the most favored due to its safety profile. However, other forms like sodium selenite and sodium selenate are also used in various products. Generally, a dosage of 200 micrograms per day is considered safe for an average adult9.
Selenium Toxicity and Neurotoxicity
Neurotoxic Effects of Selenium Overexposure
Selenium has a narrow safe range of intake, and overexposure can lead to neurotoxicity. Acute selenium intoxication can cause adverse effects on the nervous system, including lethargy, dizziness, motor weakness, and paresthesias. Chronic low-level overexposure, particularly to inorganic selenium compounds, has been associated with an increased risk of neurodegenerative diseases like amyotrophic lateral sclerosis7.
Conclusion
Selenium is an essential nutrient with both beneficial and potentially harmful effects. While it is generally safe at recommended levels, excessive intake, particularly of inorganic forms, can lead to toxicity. Current evidence does not support the widespread use of selenium supplements for cancer or cardiovascular prevention, and the safe upper limits for selenium in drinking water may need to be lowered to protect human health. Further research is needed to clarify the health risks associated with selenium exposure and to develop appropriate dietary recommendations.
Sources and full results
Most relevant research papers on this topic
Randomized, double-blind, placebo-controlled, phase III chemoprevention trial of selenium supplementation in patients with resected stage I non-small-cell lung cancer: ECOG 5597.
Selenium supplementation was safe but showed no benefit in preventing second primary tumors in patients with resected stage I non-small-cell lung cancer.
RCT
Large Human Trial
Rigorous Journal
Highly CitedThe need for a reassessment of the safe upper limit of selenium in drinking water.
The safe upper limit of selenium in drinking water should be reduced to 1 g/l due to potential health risks at lower levels than previously thought.
Highly CitedSelenium intake and cardiovascular risk: what is new?
Current evidence is insufficient to support a protective role for selenium in cardiovascular prevention, and high selenium intake may increase the risk of diabetes and hypercholesterolemia.
Systematic ReviewHighly CitedDevelopmental selenium exposure and health risk in daily foodstuffs: A systematic review and meta-analysis.
High selenium levels in meat, eggs, poultry, and seafood are essential for human health, but supplementation for prevention of cardiovascular, hepatopathies, or cancer diseases is ambiguous and may increase toxicity risk.
Meta-AnalysisEnvironmental Selenium and Human Health: an Update
Recent studies suggest selenium overexposure may be linked to type 2 diabetes, high-grade prostate cancer, and neurodegenerative diseases.
Literature ReviewHighly CitedSelenium transformation and selenium-rich foods
Organic selenium is safer than inorganic selenium and is recommended for those in selenium-deficient areas, while selenium-rich foods are the safest and best recommendation for those in selenium-deficient areas.
Selenium neurotoxicity in humans: bridging laboratory and epidemiologic studies.
Chronic low-level selenium overexposure is associated with an increased risk of amyotrophic lateral sclerosis, highlighting the need for further research on its neurotoxic effects.
Highly CitedSelenium and Lung Cancer: A Systematic Review and Meta Analysis
Selenium may reduce lung cancer risk in individuals with lower selenium levels, but should not be used as a general strategy for prevention.
Meta-AnalysisHighly CitedNutritional Selenium Supplements: Product Types, Quality, and Safety
Selenium supplements should be taken at 200 micrograms per day for an adult of average weight, based on a typical American diet.
Highly CitedEffects of 14-day oral low dose selenium nanoparticles and selenite in rat—as determined by metabolite pattern determination
Low dose selenium nanoparticles and sodium selenite both induce similar dose-dependent changes in metabolite patterns in rats, potentially reflecting altered fatty acid and protein metabolism.
Non-RCT
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