Sodium Selenite
Sodium Selenite is a tier 2 form of Selenium, used in 531 on-market products and providing 45.7% elemental selenium by weight.
531
on-market products
tier 2
quality tier
45.7%
elemental fraction
Basis: Na2SeO3, anhydrous (standard dietary-supplement/premix form; a pentahydrate at 0.300 also exists -- check specific labels)
Why this tier: Well absorbed (~80%) but less well retained than organic selenomethionine per comparative bioavailability reviews.
Source: Fairweather-Tait SJ et al., selenium bioavailability review, Am J Clin Nutr -- specific comparative % vs selenate not independently re-verified