**3. Results**

## *3.1. Included Studies and Characteristics*

Evidence for the efficacy of nutritional interventions to improve sleep in human studies is limited, with even less research reporting their effectiveness in an athletic population. The results from the literature search for studies using athletic (*n* = 4) and both healthy (*n* = 6) and poor sleeping (*n* = 10) general population cohorts are displayed below in Table 1.

**Table 1.** Characteristics of studies in athlete, and healthy and poor sleeping general population groups.



**Table 1.** *Cont.*

EEG: electroencephalogram, PSG: polysomnography, PSQI: Pittsburgh Sleep Quality Index, data presented as mean ± SD unless otherwise noted.

> Athlete studies were in mixed sport disciplines, two in cycling [21,22] and another in basketball [23]. One study did not specify the discipline the athletes participated in [24]. Three athlete studies utilized wrist actigraphy and one the Pittsburgh Sleep Quality Index (PSQI). Healthy general population studies were predominantly in male participants (*n* = 5), with one study utilizing a male and female population. Three studies used PSG to measure sleep following nutritional intervention, and two used wrist actigraphy. Poor sleeping general population studies implemented a mixture of sleep methods, from subjective sleep questionnaires to PSG. Study participants were classified as general population (poor sleepers) if they reported any of the following: subjective sleep problems; insomnia; diagnosed sleep pathology; and a PSQI score above the threshold for a 'sleep problem' (i.e., 5.0 or 6.0 depending on the specific study).

> Details of the nutritional interventions, as well as the impact these interventions on sleep outcomes are outlined in Table 2. These outcomes are detailed below in the categories of carbohydrates, protein, tart-cherry juice, and other interventions.




AVLE: *Apocynum venetum* leaf extract, GABA: γ-aminobutyric acid, GI: glycemic index, GL: glycemic load, NA: not applicable, NR: value not reported, SE: sleep efficiency, SOL: sleep onset latency, TST: total sleep time, ↑ increase, ↓ decrease, ↔ no change, \* *p* < 0.05, \*\* *p* < 0.01.
