Frequently Asked Questions About Selenium

Why should I know my selenium intake and level?
Selenium is required in small amounts in the diet for good human health. Research studies with humans suggest that a significant fraction of the adult population in the U.S. may not have the optimal selenium level. In such cases, a selenium supplement may be advisable. However, selenium is also toxic at intakes that are not greatly higher than the optimal range. Consequently, the objective of Se-Level --the Selenium Level Testing Service, is to provide an inexpensive way to measure selenium intake and level allowing an individual, with their physician, to make an informed decision regarding his or her selenium intake.

What has been discovered in case-control studies and intervention trials with selenium?
In a recent case-control study conducted by Harvard University male subjects in the lowest 20% in selenium level, as measured using the toenail as a monitor, had a three-fold greater risk of advanced prostate cancer compared to subjects in the highest 20% in selenium level. This study was published in The Journal of the National Cancer Institute (1998:90: pp.1219-24). A similar protective effect against prostate, lung and colon cancer was found in the selenium treatment group in a recent intervention trial in which the treatment group received a 200 mcg/day selenium supplement. This study was published in The Journal of the American Medical Association (1996:276: pp. 1957-63).

What is the SELECT trial?
SELECT stands for “Selenium Vitamin E Cancer Prevention Trial. This is a long-term human study to determine if a dietary supplement of selenium, or vitamin E, or both are effective in the prevention of prostate and other cancers in aging men. It is not uncommon for selenium level to decline with age even though the dietary intake may not have. The adjacent figure is a chart of a healthy male, age 50 in 1991, whose selenium level was followed for 10 years.

Why use toenails to determine selenium level?
You are what you eat; and in the case of selenium, this is reflected in your toenails. Many of the minerals that you need for good health find their way from your diet into a vast set of tissues and other substances according to need or function. For example, hair and nails are made of proteins and as they grow they incorporate selenium in proportion to its presence in your diet. Toenails work best as a selenium monitor because they are less likely, compared to hair, to be affected by non-dietary influences.

What is selenium?
Selenium is a mineral that is required in small amounts in our diets. The amount required each day is not precisely known. Recommendations made by reputable authorities range from 50 to 400 micrograms (mcg) per day.

If a little selenium is good, is a lot of selenium even better?
No. Excessive amounts of most nutrients can be harmful. In the case of selenium, symptoms of toxicity can be observed in some individuals when daily intakes reach 800 mcg. The safe and nutritious range of selenium intake is relatively narrow.

What is a microgram?
One microgram, abbreviated mcg, is one-millionth of one gram. That's not much. One of the larger grains of salt from your salt shaker would have a mass of approximately 50 mcg.

How is selenium present in the human diet?
Selenium is present in all foods generally in an organic form. Selenium-rich foods include meats, seafood and cereals. Selenium is also present in most "one-a-day" multi-vitamins that contain minerals. An increasing number of adults in the U.S. are now taking a daily selenium supplement.

How much selenium is in my diet -do I need to take a selenium supplement?
One purpose of this research is to provide you with a good estimate of your selenium intake and your resulting selenium status. We predict that the average daily intake of selenium from foods routinely consumed in the U.S. is approximately 100 mcg. But, there will be a very wide range, perhaps 50 to 500 mcg or more. An increasing number of adults, especially aged 50 and older, are taking a daily selenium supplement. By participating in this research, you will be provided valuable information that you can use with your doctor, a nutrition specialist or a registered dietitian to assess your individual decision to supplement your diet with selenium. Keep in mind that, for most people, the total daily intake of selenium should not greatly exceed 400 mcg. Consequently, a selenium supplement that provides 200 mcg/day is a prudent and safe upper limit for most adults attempting to correct a low selenium status.

What is meant by selenium level?
Your selenium status results from your individual intake and the efficiency with which your body individually absorbs and utilizes selenium. Your selenium status is expressed as the concentration of selenium in your toenails (discussed below). This concentration is directly comparable to findings from research studies that associate selenium status with risk factors for certain serious human diseases such as cancer and cardiovascular disease.

Ok, selenium is required. What does it do?
This question can only be partially answered. In one case, selenium is an active component in the body's antioxidant system. This is a complex system, with built-in redundancy, that constantly removes reactive chemicals, such as peroxides and free radicals, that are produced by the body as a normal consequence of metabolism. In another case, selenium functions in a system that is responsible for the production of the thyroid hormone needed to properly regulate metabolism. Other critical biological roles in which selenium participates are under investigation. For example, selenium may have a role in attenuating the harmful expression of viruses.

Are people in the U.S. deficient in selenium?
Conditions of serious selenium deficiency are known throughout the world; especially in those areas where the diet is limited to foods produced in regions with low selenium levels in the soil. This type of selenium deficiency is rare in the U.S. where most human diets are diverse, including components from many locales. However, there is a growing body of evidence that sub-acute selenium deficiency does exist in a significant percentage of the adult population in the U.S.

What is sub-acute, or chronic, selenium deficiency?
A sub-acute nutritional deficiency is one that occurs over a long period of time -years- making it difficult to detect.

How is sub-acute selenium deficiency related to human disease?
Some, but not all, carefully conducted nutritional health studies have linked sub-acute selenium deficiency to a higher incidence of cardiovascular disease and cancer. Likewise, many laboratory studies using cultured cells and experimental animals also support the conclusion that selenium, in consistently available quantities, protects against these diseases.

How is selenium level measured?
Over the last 20 years, through careful experimentation, we have shown that the concentration of selenium in toenails is an accurate monitor of selenium status for most people. Using the toenail as a monitor, a risk-threshold of 0.75 ppm can be established from the two studies referenced below. Subjects below this threshold had an increased risk of certain cancers in these two studies.

What is a ppm?
Ppm stands for parts per million which is a concentration measurement used to describe very low concentrations. In this case ppm refers to the micrograms of selenium per gram of toenail sample. A selenium concentration of 1 ppm will contain 1 mcg of selenium for every 1 gram (which is 1,000,000 mcg) of toenail.

How is selenium measured in the toenail specimens submitted to the SeLevel Testing Service?
Se-Level uses the same testing method that has been employed in many of the human research studies on selenium that have been conducted over the last 20 years in the U.S. This is a very accurate method referred to as Neutron Activation Analysis (NAA).

How are experiments done that relate sub-acute selenium deficiency to disease in humans?
There are basically three types of experimental designs used: population studies, case-control studies and intervention trials. Population studies have consistently shown that people living in high-selenium regions have lower incidences of cancer and cardiovascular disease. This statistical approach is used to study population groups rather than individuals. In case-control studies, the selenium status of individuals with cancer or cardiovascular disease is compared to a disease-free control subject who has been carefully matched to the case subject in all respects except presence of the disease. In intervention trials, high-risk subjects are divided into treatment and placebo groups without knowing which of the two groups they are in. The treatment group would receive a pill or capsule containing a selenium supplement and the placebo group would receive a pill or capsule identical in appearance but containing no selenium. After several years of testing, the incidence of cancer or cardiovascular disease in the two groups is compared.

Where can I learn more about selenium?
The Internet is a great place to learn about selenium -but, be careful, it is also the worst place. Remember, if it sounds too good to be true -it probably is. Reputable agencies such as the National Cancer Institute, American Cancer Society and the American Heart Association all have excellent websites on the Internet. Within these sites, you can use the search utility to find more specific information. For example try searching on "Selenium and Cancer" to access reliable information on this topic. We also have a Selenium Level Health Survey Website that you can access at SeLevel.org.