Selenium
Selenium is an essential trace mineral naturally found in soil, water, and certain foods such as fish, poultry, crab, and wheat. It plays a crucial role in metabolism, supporting thyroid function, reproduction, DNA synthesis, and immune defense. As a key component of antioxidant systems, selenium helps protect cells from damage and maintain overall health. Because soil levels vary, the selenium content of foods can differ depending on where they are grown.
Is this used to correct a deficiency or achieve supramaximal levels?
Deficiency
Is it taken for life span or health span?
Both
Is it targeting a specific disease? Or general health?
Improves headaches, mixed info about mortality and cancer
Any genetic involvement?
-
Is there a biomarker to track its effects?
Blood, urine, nails and hair
MOA of supplement
Selenium works mainly by becoming part of special proteins called selenoproteins, which protect cells and keep the body running properly. These proteins include antioxidants like glutathione peroxidase, which neutralize harmful molecules, and enzymes that activate thyroid hormones, helping control metabolism. Selenium also supports the immune system, protects cell membranes when combined with vitamin E, and may help defend against certain diseases.
Risk vs reward
+ In combination with antioxidants, may improve overall mortality and CVD related mortality
+ May improve migraine/headache frequency and severity
+ May have anti cancer properties
- High selenium intake (>300mg) may be associated with increased mortality, cancer CVD and diabetes
Evidence for it?
This meta-analysis reviewed randomised controlled trials on selenium and antioxidant supplements. Antioxidants have been promoted for reducing the risk of cardiovascular disease (CVD). The analysis found no overall benefit of selenium alone or antioxidants on CVD or all-cause mortality. However, antioxidant mixtures that included selenium were linked to reduced risk of CVD mortality and overall mortality, whereas mixtures without selenium were linked to no benefit or even harm. These findings suggest selenium may play a key role in maintaining antioxidant activity and improving supplement effectiveness.
This randomised controlled trial tested selenium supplementation (200 µg/day for 12 weeks) in patients with migraine. Selenium reduced oxidative stress markers and improved antioxidant capacity. Clinically, it lowered headache frequency, severity, and had a positive impact on quality of life. No effect was seen on psychological symptoms or headache duration. Findings suggest selenium may be a useful add-on therapy for migraine, but further studies are needed to confirm benefits and establish optimal dosage.
This meta-analysis reviewed studies on selenium exposure and cancer risk. High selenium levels in blood, plasma, or toenails were generally associated with lower risk of certain cancers, including breast, lung, esophageal, gastric, and prostate cancer. However, no protective effect was found for colorectal, bladder, or skin cancer. In contrast, randomized controlled trials of selenium supplements showed little to no benefit for cancer prevention, suggesting that supplement form, dose, and individual metabolism may affect outcomes. Potential anticancer effects of selenium are thought to involve antioxidant activity, protein regulation, and DNA stability, but these may vary by cancer type. Adverse effects of high-dose supplementation, such as increased diabetes risk, glaucoma, or dermatologic changes, highlight the need to clarify safe and effective intake levels.
Evidence against it?
This randomised trial in Denmark tested long-term selenium supplementation (100–300 µg/day) in older adults with relatively low selenium status. Over 15 years of follow-up, the highest dose (300 µg/day) was linked to increased all-cause mortality, including deaths from cancer and cardiovascular disease (CVD, conditions affecting the heart and blood vessels). Lower doses showed no lasting benefit once supplementation stopped. These findings suggest that high-dose selenium (>300 µg/day) may be harmful and should be avoided, even in populations with moderately low selenium status.
This meta-analysis reviewed 20 observational studies on selenium (Se) and diabetes mellitus (DM), including nearly 48,000 participants. Higher selenium levels were significantly associated with an increased risk of DM, particularly when measured in blood, diet, or urine. No significant association was observed for selenium measured in nails. Despite variability between studies, the findings remained consistent after sensitivity and publication-bias analyses. These results suggest that elevated selenium may be linked to diabetes risk, but further prospective and randomized trials are needed to clarify this relationship.
Best bioavailable form?
Capsule with food
Advice on taking it?
Organic form has higher bioavailability