Selenium is essential for many aspects of human health. While selenium is known to protect against cancer and cardiovascular diseases, the role of selenium in adipose development is unknown. Here we show that selenate at non-toxic concentration exhibits an anti-adipogenic function in vitro and ex vivo. In addition, selenate induced a morphological change of these cells from fibroblast-like to spindle cell shape. However, other forms of selenium, including selenite and methylseleninic acid, showed either toxic or no effect on adipogenesis and morphology change of preadipocytes. The effects of selenate on adipogenesis and cell morphology change were blunted by the treatment with SB431542, a specific inhibitor of transforming growth factor-beta 1 (TGF-beta 1) receptor, neutralization TGF-beta 1 by its antibody, and knockdown of TGF-beta 1 in preadipocytes, suggesting a requirement of TGF-beta signaling for the anti-adipogenic function of selenate. Among tested forms of selenium, selenate appears to be an effective activator of TGF-beta 1 expression in preadipocytes. These results indicate that selenate is a novel dietary micromineral that activates TGF-beta 1 signaling in preadipocytes and modulates adipogenesis. (C) 2012 Elsevier Inc. All rights reserved.