Evidence Level
Selenium research highlights its role in various health outcomes. The Nutritional Prevention of Cancer (NPC) trial (Clark et al., 1996, n=1,312) demonstrated a 52% reduction in prostate cancer risk with daily selenium yeast supplementation, though this was a secondary endpoint. However, the SELECT trial (Lippman et al., 2009, n=35,533) found no benefit for selenomethionine in preventing cancer in a selenium-replete population and suggested potential diabetes risk at 200mcg/day.
For thyroid health, a systematic review by Wichman et al. (2016, 16 studies) showed that selenium supplementation reduces TPO antibody levels in Hashimoto's thyroiditis. Recent evidence from Huwiler et al. (2024) supports this, indicating decreased TSH levels in Hashimoto patients without thyroid hormone replacement. Additionally, Sharabati et al. (2024) found that selenium supplementation significantly improved outcomes in Graves' orbitopathy.
In neurodegenerative diseases, Zhou et al. (2023) reported lower selenium levels in Alzheimer's disease patients compared to healthy individuals. However, Filippini et al. (2023) found no substantial immune benefits from selenium supplementation across nine trials. Hamdan et al. (2023) highlighted lower selenium levels in preeclampsia cases versus controls, suggesting a potential link.
Overall, selenium's effects vary by condition and baseline status, emphasizing the need for personalized approaches.