How much selenium from food and supplements do we need on a daily basis? Which bio-markers of optimal selenium status seem to be most useful to answer this question? Dr. Rachel Hurst and Dr. Susan J. Fairweather-Tait, Norwich Medical School, United Kingdom, and their colleagues set out to find answers. The design of their study is very interesting.
They enrolled 119 healthy British men and women aged 50 – 64 years in a randomized, double-blind, placebo-controlled study that lasted 12 weeks [Hurst]. They excluded the following persons from the study:
- smokers
- overweight people
- people with already high plasma selenium status
- people with long-term illnesses
- people on various medications
- people unwilling to discontinue taking vitamins and herbal remedies at least one month prior to the start of the study
The 119 study participants received either placebo or one of the following treatments:
- selenium-enriched yeast tablets containing 50, 100, or 200 micrograms of a patented organic selenium (SelenoPrecise® preparation delivered by Pharma Nord, Denmark)
- selenium-enriched onion meals that provided the equivalent of 50 micrograms of selenium per day
- unenriched onion meals that provided the equivalent of less than 4 micrograms of selenium per day
Measurements of selenium
Remember: Selenium is a trace element. We measure its intake in micrograms per day, not milligrams. We measure selenium status in plasma and serum in terms of micrograms per liter (or equivalently, in nanograms per milliliter). Selenium in toenails or hair, then, we measure in micrograms per gram.