A 2015 longitudinal design study evaluated the influence of nightly sleep duration, sleep quality and sleep onset latency on sexual response and activity in 171 women. Results revealed that longer sleep duration was associated with greater next day sexual desire. It was also found that women with longer average sleep duration reported improved genital arousal than women with shorter average sleep length.
Altered sleep drives alterations in gut microbiome composition, impeding libido and compromising vagal tone—integral for governing countless regulatory processes between the body and brain. Millions of neurons that line the GI tract constantly send signals to the brain relative to the physiological state of the body. An imbalanced microbiome interferes with the ability to synthesize molecules conducive to quality sleep, libido and mood, further causing dysregulation in mind-body signaling; whereas sufficient sleep decreases levels of cortisol and promotes microbial diversity and balance, thus supporting mood and libido.
The neurobiology of sexual desire is an intricate interplay between excitatory and inhibitory systems including—dopaminergic, serotonergic and GABAergic, key neuromodulators widely distributed throughout the body and brain, having integral functions in regulating sleep, libido and mood. They are involved in neural and hormonal signaling bidirectionally via the BGMA. Libido is influenced by synchronicity and balance among these neuromodulators and other regulatory hormones.
Imbalances and lack of diversity in the microbiome, therefore, can largely impede mood, sleep libido, and hormonal health. In fact, the gut microbiome has gained recognition as “the second endocrine system,” further underscoring its regulatory functions.
A 2024 analysis of a large U.S. claims database of men 40-70 years old revealed that testosterone deficiency was more evident in those diagnosed with sleep apnea, insomnia and circadian rhythm dysfunction compared to controls. Erectile dysfunction (ED) was also more likely to be found in men diagnosed with these conditions, in comparison with healthy controls. These results highlight the impact altered sleep has on hormones and libido.
Libido is regulated by key areas of the brain through the action of various hormones and neurotransmitters. At the level of the CNS, microbiota influence their host by producing enzymes that impact the activity of sex dependent hormones and neurotransmitters, supporting crosstalk between the gut and the brain.
Serotonin is found extensively in the GI tract, with an estimated 95% of total serotonin located in the cells of the gut, where it modulates intestinal movements. The remaining is produced in serotonergic neurons in the CNS, having roles in regulating mood, appetite, sleep, sex and muscle contraction. Serotonin is considered an inhibitory neurotransmitter as it suppresses the ability of the excitatory systems to be activated in increased amounts.
Neurotransmitters associated with libido such as serotonin, dopamine and norepinephrine have been shown to be synthesized by various microbiota. Enterococcus spp., Streptococcus spp., Escherichia spp., Lactobacillus plantarum, Klebsiella pneumonia, and Morganella morganii are microbial strains shown to produce serotonin; while Lactobacillus, Serratia, Bacillus, Morganella and Klebsiella have been indicated to generate dopamine. This emphasizes the importance of having optimal diversity and balance in the gut.
A 2019 study discovered that total microbiome diversity, as evidenced by measures of richness, Shannon diversity and inverse Simpson diversity, were associated with sleep efficiency and total sleep time. Analysis of microbiome composition of 26 males indicated that abundance of phyla bacterial strains, Bacteroidetes and Firmicutes were positively correlated with these measures. These microbiota have been associated with improved sleep quality, and have also been shown to produce GABA, supporting regulation of healthy sleep and arousal.
Further microbiota strains that have been implicated to synthesize GABA include Lactobacillus and Bifidobacterium. Sufficient amounts of GABA have integral functions in modulating sleep, gut functioning and libido through its role as an inhibitory neurotransmitter.
Results from a 2021 case-controlled study in The Journal of Medical Internet Research explored the connection among particular microbiota and reductions in libido. Samples were collected from 24 women with hypoactive sexual desire disorder (HSDD), characterized by low desire for sexual activity, in addition to 22 healthy controls. RNA gene sequencing and metabolome analysis results showed altered metabolic profiles and microbial composition in those with HSDD in comparison to healthy controls. In particular, it was found that women with HSDD had reduced amounts of Ruminococcaceae, a microbial strain associated with improved sex drive. Similar results were echoed in a 2022 review of 13 studies demonstrating that in healthy women, higher estrogen levels were associated with lower abundance of Ruminococcaceae, and increased overall microbial diversity, in comparison to women with altered hormonal profiles such as in PCOS.
Evidence from a 2024 study in The Journal of Microbiology Biotechnology, demonstrated that men with ED had different microbial phenotypes than controls. Samples were collected from 53 patients with ED and 32 healthy controls for analysis utilizing rRNA gene sequencing. The results revealed that ED subjects had significantly lower gut microbial diversity compared to controls. It was also observed that IL‐6 levels were higher in men with ED compared to the control group. Similar findings were revealed in a 2021 study involving gene sequencing of 30 ED and healthy donor stool specimens. Significant differences in microbial composition and diversity were exhibited, with marked reductions in the ED group.
The gut microbiome, libido and sleep are complex, interconnected aspects of well-being. Restorative sleep promotes healthy microbial diversity and balance, having beneficial effects on mood and libido, supporting an enriched quality of life.
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