Table 7. Mental Health and neurological disorders.

	Author, year, Location	Study design	Age	% male	HIV Virological Control	NCD Examined	Main findings
1	Lyons 2011, USA	Cross sectional study of PWH with nadir CD4 count <300 (n = 97)	Years (mean, SD) 47.1 ± 8.0	76%	14,924 (undetectable/ suppressed, 843,720) (median, IQR) copies/mL	HAND diagnoses were determined using AAN diagnostic criteria Plasma and CSF HIV RNA	Elevated plasma sCD14 seen with GCI, impaired testing in attention and learning domains compared to unimpaired subjects. Plasma sCD14, Plasma and CSF VL, current and nadir CD4 count, and plasma CCL2 and LPS levels did not differ by HAND diagnosis
2	Zhang 2019, China	Cross sectional study of PWH (n = 85)	Years (median, IQR) 33 (27–41)	HAND 89.7%, non-HAND 87.8%	39,810.72 (6,309.57, 100,000) (median, IQR) copies/mL	HAND diagnosis by MoCA cut-off 26/30	The HAND group had lower α-diversity than the non-HAND group, but this did not remain when matched for confounders. No significant differences in the β- diversity or predictive function of the gut microbiota was found between the HAND and non-HAND groups.
3	Ellis, 2022, USA	Case control study of 1.PWH (n = 226) and 2.HIV negative (n = 101)	Years (mean SD) 1. 52.4 ¬± 11.8, 2. 51 ¬± 16.7	87.60%	90% undetectable/ suppressed viral load	DSP diagnosed by clinical exam. Self-reporting tool and clinical examination for DNP diagnosis.	Severe DNP was associated with lower α-diversity but not changes in β- diversity. Found relative increases in the ratios of Blautia and Clostridium to Lachnospira in PWH with DNP. Rates of DSP and DNP were not different in MSM and non-MSM PWH, however, MSM PWH had less severe DNP than non-MSM.
4	Perez-Santiago 2017, USA	Cross sectional study of 1. PWH (n = 96) and 2. HIV negative (n = 30)	Years (median, IQR) 1. 55 (49.5–61.3), 2. 58 (48.8–69)	88%	Not reported	HAND, diagnosed by neuropsychological assessment and self-reported depression screening.	PWH with HAD had significantly lower levels of Firmicutes and higher levels of Bacteroidetes Higher levels of F. prausnitzii is associated with higher depression and higher levels of B. caccae are associated with better cognition
5	Taylor 2020, USA	Cross sectional study of 1. PWH (n = 219), 2. HIV/ HCV co-infection (n = 48) and 3. uninfected controls (n = 106)	Years (mean, SD) 1. 51.7 (12.0), 2. 53.8 (9.1), 3. 51.2 (16.3)	1. 88%, 2. 85%, 3. 60%	93% undetectable/ suppressed viral load	DSM-IV diagnosis of lifetime major depressive disorder was evaluated using CIDI and BDI-II.	The HIV/HCV group had a significant difference in bacterial composition between those who met lifetime diagnostic criteria for MDD versus those who did not and were enriched in primary and secondary bile acids. Depression-related taxa found in HIV/HCV group include Enterobacteriaceae, Alistepes onderdonkii), Bacteroides and Parabacteroides distasonis.
6	Dong 2021, China	1. PWH with NCI (n = 67) and 2. without NCI (n = 35) from the Comparative HIV and Aging Research in Taizhou (CHART) cohort study	Years (mean, SD) 1. 54.6 +- 9.7, 2. 55.3 +- 9.3	82.10%	Not reported	Neurocognitive tests for global cognitive score. Zung Self-Rating Depression Scale. Jenkins four-item sleep questionnaire for insomnia. Fried Frailty criteria Vitamin D Measurements CIMT measurement by US	No difference in α-or β- diversity between the NCI and non-NCI groups. The NCI group had higher CIMT, carotid plaque, cholesterol and increased abundance of Spirochaetes and Epsilonbacteraeota than non-NCI. 14 metabolites [bile acids (BAs), glycerophosphoinositols, fatty acids, eicosanoids, and fatty amides] were significantly increased in the NCI group. There were negatively correlated with Faecalibacterium, Corprococcus_2, and Ruminococcus_1 and positively correlated with Klebsiella Four vitamin D metabolites, five terpenoids and resolvin D1 were significantly decreased in the NCI group. These were positively correlated with Faecalibacterium, Corprococcus_2, and Ruminococcus_1, and negatively correlated with Klebsiella. Vitamin D level was negatively associated with CIMT and with Ruminococcus_1, Eubacterium_eligens_group, and uncultured_bacterium
7.	Hua, 2023	1. PWH (n = 302) and 2. HIV negative (n = 144)) from the WIHS Cohort.	Years (mean, SD) 53.1	0%	74.2% undetectable/ suppressed viral load	A neuropsychological test battery assessing the following domains: learning, memory, psychomotor speed, attention/working, motor function, verbal fluency and executive function	α-diversity was higher in women with NCI compared to those without. No differences in beta diversity. Found a higher abundance of Methanobrevibacter, Odoribacter, Pyramidobacter, Eubacterium, Ruminococcus, and Gemmiger, and lower abundance of Veillonella were associated with NCI, this was more profound in PWH compared to HIV− women. Most associations with bacterial taxa were observed for learning and memory.

Abbreviations: AAN, American Academy of Neurology; BDI-II, Beck Depression Inventory-II; CIDI, Composite International Diagnostic Interview; CIMT, Carotid intima media thickness; CSF, cerebrospinal fluid; DNP, distal neuropathic pain; DSP, distal sensory polyneuropathy; GCI, global cognitive impairment; HAD, HIV-associated Dementia; NCI, neurocognitive impairment; HAND, HIV-associated neurocognitive disorder; LPS, lipopolysaccharide; MoCA, Montreal Cognitive Assessment; MSM, men who have sex with men; sCD14, soluble CD14; US, ultrasound; VL, viral load