The trace mineral selenium helps to produce the antioxidant glutathione and works in concert with vitamin E to shield cell membranes from damage. The University of Maryland Medical Center reports low levels of selenium have been linked to cancer and that people who live in areas with large amounts of this nutrient in the soil appear to have lower rates of cancer. Whether supplementing with selenium will help prevent cancer or serve as a treatment for other purported uses such as heart disease, rheumatoid arthritis, depression and asthma has not been firmly established. If you believe taking selenium will address a particular health concern, discuss the appropriateness of using this supplement with your doctor. Taking larger amounts of selenium might cause adverse effects.
Dosing Guidelines
Staying within the suggested dosing guidelines can help prevent adverse effects associated with selenium supplementation. The Beth Israel Deaconess Medical Center reports most studies use between 100 mcg and 200 mcg daily, though some have used more than this. This dose appears to be safe for most people, though negative reactions are always possible at any dose. The University of Maryland Medical Center reports the tolerable upper intake limit as 400 mcg; you should never use more than this without the supervision of your doctor. In fact, the center advises you to consult with your doctor before taking selenium in amounts larger than the recommended daily intake of 55 mcg for anyone 15 and older and 70 mcg for pregnant and lactating women.
Increased Risk of Diabetes
The University of Michigan Health System reports one study testing the effects of selenium for preventing recurrences of skin cancer found a statistically significant increased risk of developing diabetes in subjects taking selenium compared to the placebo group. They were taking 200 mcg over the course of several years. This alone, however, is not sufficient to conclusively link prolonged supplementation of selenium with an increased risk of diabetes. If you have diabetes or have an increased risk of getting it, talk to your doctor about using selenium and a suggested dose.
Reduced Vitamin C Absorption
The Memorial Sloan Kettering Cancer Center reports high doses of selenium can reduce vitamin C absorption. Make sure to eat plenty of vitamin C-rich foods or use a supplement to ensure your body can get the amount it needs.
Toxicity
Selenium appears to pose a risk of toxicity at extremely high doses --- 900 mcg or more. Symptoms include vomiting, nausea, emotional instability, nervousness, depression, irritability, fatigue, weight loss, hair loss and fingernail loss.
Other Safety Concerns
The Beth Israel Deaconess Medical Center reports excess selenium intake might cause elevated cholesterol levels. If you have liver or kidney disease, always clear the use of supplements with your doctor. Since these organs have a particular sensitivity to what you put in your body when operating in a diseased state, doses of supplements normally considered safe for others could prove dangerous to you. Your doctor can suggest a proper dose if he approves the use of selenium. Do not use selenium without your doctor's approval if have impaired thyroid function or currently suffer from skin cancer or have had it in the past. Selenium might negatively interact with several medications, such as blood-thinning drugs, sedatives, cholesterol drugs and chemotherapy agents.
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