*3.2. Study Characteristics*

All 10 studies included in this meta-analysis were randomized, double-blind, placebocontrolled trials, with 526 participants, including 272 in the selenium group (experimental group) and 254 in the control group. The treatment period ranged from 4 to 24 weeks. All 10 studies were conducted in Iran. Except for Faghihi 2014 [48], the remaining nine studies have completed clinical trial registration. Faghihi 2014 [48] reported participants' selenium concentration as deficient state at baseline, and the remaining studies did not report participants' selenium status. In the included studies, the forms of selenium supplementation were mainly selenium yeast and sodium selenite, but three studies did not mention the form of selenium supplementation. Five studies [37,41,43,45,48] recruited patients with diabetes mellitus or complications of diabetes mellitus (e.g., diabetic nephropathy), three studies [30,42,44] recruited patients with cardiovascular disease, one study [46] recruited patients with diabetes mellitus combined with coronary heart disease, and one study [49] recruited obese patients (Table 1).

**Figure 1.** PRISMA flow chart for selection and screening of the studies.


**Table 1.**

Characteristics

 of the included studies.


M: Male, F: Female, I: Intervention,

 C: Control, NR: Not reported, RCT: Randomized

 controlled trial.

**Table 1.** *Cont.*

*Nutrients* **2022** , *14*, 4933
