This preclincal study published in 2021, assessed the pharmacokinetics of long term selenomethionine supplementation (200 mcg over 32 months).
Results indicated that total selenium content was 80% higher with supplementation. As expected, the Se mass of most pools increased with SeMet supplementation, because SeMet is incorporated into proteins in place of methionine.
References:
Patterson, B. H., Combs, G. F., Jr, Taylor, P. R., Patterson, K. Y., Moler, J. E., & Wastney, M. E. (2021). Selenium Kinetics in Humans Change Following 2 Years of Supplementation With Selenomethionine. Frontiers in endocrinology, 12, 621687. https://doi.org/10.3389/fendo.2021.621687