Equisetum arvense tea (TEA) contains high concentrations of silicon and has been used in folk medicine for the treatment of inflammatory ailments. We examined the resorption of silicon after TEA consumption. Safety and immunological effects were secondary outcomes. A monocentric, randomized, three-armed pilot study was conducted with 12 voluntary, healthy, male subjects. The study is registered in the German register for clinical trials (DRKS-ID: DRKS00016628). After a low silicon diet for 36 hours, 1000 mL TEA1 with approximately 200 000 µg silicon/L, TEA2 with approximately 750 000 µg silicon/L, or Si-low-Water (approximately 10 - 10 000 µg silicon/L as a control) were ingested on three consecutive days. Blood and urine samples were collected at baseline, day 1 examining silicon kinetics, day 3 examining silicon accumulation, and day 8 (safety, immunological parameters). Si-low-Water intake did not change silicon serum (Cmax 294 µg/L) or urine (19 000 µg/24 h) concentrations compared to baseline. Cmax was 2855 µg/L for TEA1 and 2498 µg/L for TEA2; tmax was 60 and 120 min, respectively. Silicon accumulation did not occur. Urine silica within 24 h (E24 h) was higher after TEA2 compared to TEA1 ingestion (142 000 vs. 109 000 µg/24 h). Serum silicon levels at t = 120 min differed significantly after intake of TEA2 or intake of Si-low-Water (p = 0.029). The immunological parameters did not show any significant changes indicating immunosuppressive effects in volunteers. TEA1 was well tolerated, while TEA2 caused diarrhoea in 4 subjects. Our investigations show that intake of TEA1 leads to significant rise in serum silicon concentration.
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