Differential responses to selenomethionine supplementation by sex and genotype in healthy adults

Randomized, four-arm, 12-month intervention in healthy selenium-adequate adults living near Grand Forks, North Dakota, USA. The source packet describes 106 men and 155 women overall, with mean age 49.6 years and mean BMI 27.4 kg/m2; active intervention arms received oral SeMet at 50, 100, or 200 mg/d.

Oral L-selenomethionine was given daily for 12 months in three active dose groups: 50 mg/d, 100 mg/d, and 200 mg/d. Capsules contained SeMet with dicalcium phosphate excipient; the trial also included a 0 mg/d comparator arm.

SeMet supplementation produced dose-dependent increases in selenium body pools, including plasma selenium, urinary selenium, and buccal cell selenium, with responses plateauing by about 9 to 12 months. GPX3 activity and SEPP1 levels did not change significantly. Urinary selenium excretion increased more in women than in men, by 74% higher (P=0.001), and was also higher in participants with the GPX1 679 T/T genotype than in GPX1 C/C, by 59% higher (P<0.006). Overall, the most responsive biomarkers were those reflecting body selenium pools rather than plasma selenoproteins, and the authors concluded that sex and GPX1 genotype influence selenium metabolism and may justify personalized supplementation strategies.

The population was small, healthy, and selenium-adequate, which limits generalizability to deficient or clinical populations. Sample size per active arm was not explicitly reported in the source packet, and the trial compared multiple doses over 12 months without evidence of benefit for GPX3 or SEPP1. The absence of adverse effects is reassuring, but some participants dropped out and subgroup findings raise the possibility of effect heterogeneity.