In 2018, colorectal cancer is the standard type of cancer ranked second in mortality and third in incidence globally (42). Approximately 70% of the human microbiome resides inside the colon (43). The genetic heritability of CRC is as low as 10–12%, which explains the role of microenvironment in the development of sporadic CRC (44). Several studies indicated the next part of gut microbes in CRC development. Microbial species such as Clostridium, Bacteroides, Enterococcus, and Escherichia genera were found to induce carcinogenesis by 1,2-dimethylhydrazine (45). A fecal transplant further established the role of gut microbiota in colorectum from patients with CRC to germ-free mice, which developed tumors when supplemented with azoxymethane to induce colon neoplasia (46). The studies showed the abundance of procarcinogens microbes belonging to Fusobacterium, Bacteroides, Porphyromonas, and Escherichia class with declined protective microbes such as Roseburia in patients with CRC (47–49).

The gut microbiome impacts on the development of CRC via different mechanisms, which include the microbial factors (genotoxins or metabolites). The drivers in this mechanistic pathway are SCFAs, PRRs, and several chemotactic factors (CCL17, CCL20, CXCL9, and CXCL10). Cytolethal distending toxin (CDT) and colibactin are commonly known toxins produced by Escherichia, Campylobacter, and Enterobacteriaceae spp. Some microbes may act as carcinogenic (driver microbes) and some as opportunistic bacteria (passenger bacteria) in the tumor microenvironment. This host microorganism interaction leads to the activation of several downstream signaling pathways, resulting in CRC development (50).

To describe the polymicrobial interaction in the tumor environment of CRC, Tjalsma et al. put forward the driver–passenger model. This model proposed that the driver bacterium such as Bacteroides fragilis and Escherichia coli in the tumor microenvironment releases genotoxins that promote inflammation causing premature transformations in adenocarcinoma cells thereby causing a favorable tumor microenvironment for the growth of passenger microorganisms. Passenger bacterium such as Streptococcaceae and Coriobacteriaceae proliferate in the tumor microenvironment in such a way that can outgrow the other bacterial species. The development of microbial biomarkers depends on different tumor stages. Identification of various bacterial strains surviving across different carcinogenic stages is also important in this aspect. While the driver bacteria can be directed against colorectal cancer, the passenger bacteria is associated with disease initiation, propagation, and response to treatment (51).

Ingestion of non-digestible carbohydrates leads to the production of SCFAs due to microbial fermentation in the colon. Butyrate is known as an anti-inflammatory and tumor-suppressive entity that induces apoptosis in CRC. Reduced levels of SCFAs are linked with a high risk of CRC, advanced colorectal adenoma, and ulcerative colitis development (52–54). For screening CRC, accurate biomarkers are needed, which if detected at early stages, can be treated with clinical therapies. The fecal immunochemical test (FIT) is currently used to detect CRC, with the significant drawback being 79% sensitive and 25–27% susceptible to detect advanced colorectal adenomas. Several studies have reported the utilization of microbial species to detect CRC using butyryl-Co-A dehydrogenase from F. nucleatum and RNA polymerase B subunit from P. micra quantified by PCR (49). Several reports established the association between oral microflora such as Prevotella and Streptococcus and CRC opening a new array for predicting CRC.

In recent years, a new dimension of understanding has emerged on the pathogenesis of cardiovascular diseases, beyond the interaction of nutrition and genetic variation. Preclinical and clinical evidences have revealed that gut microbiota influences the pathogenesis of atherosclerosis (55). An involuted indication involves both inflammatory and metabolic pathways which are leveraged by the gut microbiota in three pathways: (i) acceleration of plaque formation via turning on the inflammatory immune response caused by local or distant infection, (ii) generation of ominous bacterial metabolites (viz., TMAO) from specific components of diet, and (iii) disruption of cholesterol and lipid metabolism routes of the host (56). As evident from the scientific studies discovering the presence of bacterial DNA in plaques, both direct and distant infections contribute to atherosclerotic plaques development. These bacteria are also found mostly in gut and oral cavity (57). To our intrigue, 16S rRNA analysis revealed a large abundance of Firmicutes and Proteobacteria phyla in the atherosclerotic plaques (58). Besides these, pathogenic Helicobacteraceae and Neisseriaceae were also found to be more prevalent in patients with symptomatic atherosclerosis (59). 16S shotgun sequencing experiment of fecal samples from healthy individuals, patients with atherosclerosis, and healthy volunteers with symptomatic atherosclerosis was found to vary in various aspects. Patients with disease symptoms were reported an enhancement in genus Collinsella, whereas Eubacterium and Roseburia were increased in controls. Moreover, gut dysbiosis in the patients was accompanied by an augmentation of an abundance of inflammatory genes (60). The abundance of Firmicutes got increased and Bacteroidetes got decreased when compared with healthy volunteer (61). Several preclinical and clinical studies have suggested strong causal links between gut microbiome and atherosclerosis. Compelling evidence is accumulated, which emphasizes a correlation with the CutC enzyme (encoded by gut microbe), known to convert carnitine and phosphocholine compounds to trimethylamine (TMA). Thereafter, it reaches the host liver and gets oxidized to trimethylamine oxide (TMAO), which was proven to affect cholesterol metabolism-enhancing cholesterol accumulation in macrophages and atherosclerosis development (6).

It is also evident from a few studies that patients with atherosclerosis have modified lipid metabolism, and plasma cholesterol levels are correlated with bacteria in the gut and oral cavity (57). Mechanistically, gut microbiota modulates cholesterol and lipid metabolism through altering bile acids and its farnesoid X nuclear receptor (FXR). It is now understood that bile acids help in the absorption of dietary lipids and fat-soluble vitamins. In the liver, primary bile acids are generated by being conjugated to taurine or glycine, formation of secondary bile acids is achieved by intestinal decoupling by bacterial bile salt hydrolase followed by colonic metabolism. However, gut microbial modulation of bile acid composition and signaling in FXR-expressing tissues in atherosclerosis is not been fully explored yet and remains as a matter of intense investigation (62). There is no denying the fact that a perpetual interaction between host and gut microbiota over a life span would determine the speed of disease propagation. To establish the causal relationship between a species or metabolites and atherosclerosis, it is, therefore, imperative to establish proper linkages of microbiota to distinct functions.

The widespread presence of obesity in the majority of the population increases the development of other metabolic NCDs such as CVD and T2DM (63). These disorders alone contribute to approximately 80% of premature mortality, with diabetes mellitus affecting nearly 347 million people globally (64). Lifestyle, obesity, malnutrition, and other health-related disorders contribute majorly to CVD and T2D in the Indian population (65). Recent studies showed the link between diet and the microbiome inhabiting the gut and their contribution to food digestion and absorption. Studies reported that the Bifidobacteria, Prevotella, and Akkermansia majorly inhabit individuals consuming the plant-based fiber-rich diet. In T2DM, Bacteroides, Akkermansia, Ruminococcus, and Faecalibacterium were found in abundance, while Roseburia were found to be in lower concentrations. Intestinal microbiota, disruption in the intestinal barrier, and inflammation affect the development of diabetes and obesity. Alteration in gut microflora due to external factors such as diet affects the metabolism causing diabetes and insulin resistance. LPS secreted by Gram-negative gut microflora produces inflammatory cytokines causing inflammation through TLR4 signaling pathway (66). The increased LPS was also found to destroy the integrity of the intestine, causing high LPS absorption. While acetic acid and butyrate have been reported to enhance the intestinal barrier functioning linked to insulin resistance and inflammation, SCFAs are also known to regulate glucose homeostasis through G protein activation of the Langerhans cells (67, 68).

When fecal bacteria transplantation was performed in insulin-resistant patients from insulin-sensitive patients, significant insulin sensitivity was observed with an abundance of butyrate-producing bacteria, which was observed on analysis as Faecalibacterium prausnitzii (69). Gut microbes transform the bile acid synthesized in the liver into secondary bile acids through enzyme metabolism. These secondary bile acids regulate insulin sensitivity through Farnesoid X receptor (FXR) and the Takeda G protein-coupled receptor 5 (TGR5) (70). Branched-chain amino acids (BCAA) are a critical predictive marker for T2D and are associated with the risk of developing T2D (71, 72).

A high-fat diet with BCAA also leads to insulin resistance has also been reported. Other studies with humans supported that BCAA with a high fiber supplementation escalates the risk of T2D development. The microflora associated with BCAA synthesis is majorly Prevotella copri and Bacteroides vulgatus (73).

Osteoporosis is a disease often marked by decreased bone mass per unit volume and wear and tear of bone tissue microstructure, increasing the susceptibility to fracture. It can occur irrespective of age and sex and is common in postmenopausal women. Nutrition, heredity, lifestyle, and hormone levels are known to contribute toward the development of the malady. The four distinct phases of the bone remodeling cycle comprise initiation, resorption, reversal, and formation. Endosteal cells, osteoclasts, osteoblasts, and osteocytes together form the bone remodeling units that participate in the bone renewal process (74). The main regulators participating in bone metabolism include vitamin D, estrogen, inflammatory factors, and parathyroid hormones. Menopausal women often manifest primary osteoporosis thereby rendering menopause as a major risk factor of the same (75). In contrast, pathological factors such as inflammatory bowel disease, parathyroid disease, glucocorticoid therapy, type 1 diabetes, arthritis, and smoking lead to secondary osteoporosis’s onset (76).

The gut microbial composition can surely influence nutrient absorption. Upraised abundances of microbes such as lactobacillus and bifidobacteria were shown to inhabit the human intestinal tract, promoting the absorption of phosphorous, calcium, and magnesium, leading to increased bone mineral density (BMD) (77). It was also shown that the diversity of gut microbes could affect the pH of the gut, further affecting nutrient absorption, specifically, calcium absorption. These microbes also participate in bile acid metabolism and vitamin B and K synthesis, playing a crucial role in bone health and calcium absorption. The gut microbiota catabolizes the macromolecules into simpler components facilitating the ease of nutrient absorption by increasing the bone density and delaying the onset of osteoporosis (78).

Moreover, SCFAs produced by the microbial fermentation of dietary fibers regulate bone mass and osteocyte formation. Bone loss was prevented and bone mass was increased in mice fed with SCFA with ameliorated osteoporotic condition. The importance of a balanced diet in the maintenance of bone health was proved when the fecal transplantation was performed from a high-fat diet mouse to a healthy mouse that adopted the gut microflora, causing osteoporosis in healthy mice. These studies showed that the high-fat diet impairs the micro-environment of bone marrow, causing the poor reorganization of hematopoietic stem cells. HFD was also found to activate PPARg2, thereby enhancing bone marrow lipogenesis and impairing osteoblast formation (79).

According to a few recent studies, a commonality related to immune component is shared between osteoporosis and inflammatory joint disease. Function of gut microbiota may be regulated by Th17/T-reg cells. Several gut bacterial species such as Clostridium, Bifidobacterium, Helicobacter, Bacteroides, and Lactobacillus facilitate the generation of Treg cells in the colon. SCFAs, vitamin A, and estrogen are key players in maintaining the dynamic balance between Th17/T-reg cells inhibiting osteogenesis (80).

Polycystic ovarian syndrome (PCOS) is an endocrino-pathological disorder in which the ovaries produce exceptionally abnormal levels of the male hormone androgen. With hyperandrogenism, insulin resistance, menstrual disorders, hirsutism, infertility, and anovulation, the principal facets of the syndrome, PCOS is prevalent in 5–7% of women population in their reproductive age (81). PCOS is also accompanied by disorders such as hypertension, endometrial carcinoma, type 2 diabetes mellitus, glucose intolerance, dyslipidemia, insulin resistance, dysfunctional bleeding, cardiovascular disease, and pregnancy loss in the majority of the patients (82). Neuroendocrine, environmental factors, metabolic and immune dysfunctions, and genetics play crucial roles in developing PCOS. While polycystic appearing ovary (PAO) is preclinical, it does not fall under PCOS. In contrast, factors such as insulin resistance, obesity, dopaminergic dysregulation, and stress make the transition of PAO to PCOS in women (83).

Studies showed that the diversity of gut microbes in patients with PCOS is significantly reduced compared with control groups (84). Several genes participating in PCOS development are found to play a role in carbohydrate metabolism and steroid synthesis pathway, thus creating a link between metabolic factors and possible mechanism of PCOS development (85). The occurrence and progress of metabolic and endocrine imbalances in PCOS are affected by the intestinal microflora. In a pilot, clinical study that compared the microbiome from patients with PCOS to control patients, a decrease in Tenericutes bacterium (ML615 and S247) was observed (86). It was shown that the gut microbiota disorder in obese patients increases the energy intake of the host as the SCFAs produced from the glucose conversion stimulate the peptide YY release, which prohibits intestinal peristalsis, diminishes the pancreatic discharge, and stimulates energy absorption in the intestine (87, 88). Turnbaugh et al. showed that the Firmicutes population in the intestine was higher, and Bacteroides was lower in obese mice that increased the intake and absorption of energy and exhibited the symptoms of obesity (11). Butyrate, acetate, and propionate are the major SCFAs that activate peroxisome proliferator-activated receptor gamma (PPAR-γ), which regulates fatty acid and glucose uptake. SCFAs in the intestines, skeletal muscles, fat, immune system, nervous system, and liver are found to impede appetite-stimulating hormone (ASH) secreted by gastric mucosa that is known to inhibit the secretion of GnRH and other sex hormones. ASH is known to inhibit the CYP19A1 expression that inhibits the conversion of androgen to estrogen. Lower ASH correlates with enhanced androgen levels causing hyperandrogenemia (89). Figure 4 highlights various mechanisms responsible for PCOS development.

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease observed in the past few years. It is indicated by hepatic steatosis which may advance to liver cirrhosis, hepatocellular carcinoma, and non-alcoholic steatohepatitis. Obesity and type 2 diabetes are the major factors that lead to NAFLD development (90). It has been shown that gut dysbiosis correlates with NAFLD. The composition of the gut microbiome differs from NASH, cirrhosis, and fibrosis. The intestinal barrier is compromised due to nutrition stress in NAFLD, which leads to translocating of the gut microbe and their metabolites into the blood system causing hepatic inflammation and cirrhosis (91).

WHO elucidated obesity as unrestrained body fat accumulation leading to increased body mass index (BMI) often caused by an imbalance between energy consumed and expended, measured in terms of calories. In general, BMI greater than 25 is considered as overweight and beyond 30 is known as obese (92, 93). A recent survey by National Health and Nutrition Examination (NHANES) found that more than two in three adults were overweight or had obesity (94). It is on a dramatic rise in low- and middle-income countries, mostly prevalent in urban areas. Nonetheless, obesity is a global burden for our health system and a leading cause of the development of metabolic diseases such as diabetes, atherosclerosis, osteoarthritis, gout, high blood pressure, and some cancers. The shifts in gut microbial composition have been found to play an important role in obesity (95). In 2016, Cindy D. Davis et al. demonstrated that obesity can be attributed to alterations in the composition of gut microbes such as diminished microbial diversity or mutations in bacterial genes and associated metabolic pathways. Obese mice exhibited a higher percentage of Firmicutes and half the amount of Bacteroidetes, with concurrent augmentation in microbial genes entailing polysaccharide breakdown compared to thin siblings (95).

The gut microbiome provides several benefits such as aiding in digestion and food absorption, metabolization of fibers to produce beneficial SCFAs, nutrient and vitamin synthesis, regulation of host immunity, and integrity of intestine. The gut microbial composition depends on the acidity of the small intestine, stomach and colon, lifestyle, and racial and geographical differences. The microbial composition shifts its function from beneficial to the host toward causing inflammation in individuals with morbid obesity. A similar trend was observed during aging that caused diseases such as CVD, Alzheimer’s disease, insulin resistance, T2DM, and frailty. Compositional differences between these gutbacterial species were observed more in aged population than young individuals. The reduction in gut microbiome diversity was observed concerning age in aged mice, having reduced bacterial biosynthesis of biotin and cobalamin, enhanced creatine degradation and SOS genes associated with DNA repair.

A model, hypothesized to examine the impact of the gut microbiome on aging, was later proved to be correct. It states that microbial dysbiosis increases the intestinal permeability triggering the inflammatory response of the host. This induction of inflammation affects the microbial composition, further promoting dysbiosis creating a feed-forward loop (96). Gut microbial population and its density have influenced systemic inflammation (97). Extrinsic elements including diet and lifestyle determine microbial composition and related dysbiosis (98). When tested on model organisms, the high-fat and meat-dominated diet correlate with microbial dysbiosis (99). In contrast, the Mediterranean diet was shown to induce a healthy gut microbiome (100).

Many gut microbiome and biomolecules synthesized by them, such as SCFAs, vitamins, gut-derived hormones, and other chemical compounds, affect life span and health (101). Table 1 mentions the microbes that modulates the life span.

Colorectal cancer (CRC) still remains an arduous burden for our health system (118). In 2020, 935,000 deaths have been reported by WHO in both men and women. American Cancer Society (ACS) anticipated that number of new patients with CRC would reach around 2.4 million in the world until the year 2035 (119, 120). Global research would not deny that infection and dysbiosis are closely related to CRC and some nutraceutical compounds including phytochemicals, probiotics, prebiotics, and postbiotics have displayed prominent immunomodulatory roles in the prevention and management of the same. For instance, quercetin, silymarin, and curcumin have shown promising immunomodulatory effects against CRC management, viz., quercetin activated the dendritic cell and thereby antigen presentation, curcumin induced apoptosis and silymarin inhibited Wnt signaling in human colorectal cancer cells (121–124). Few research groups also found some phytonutrient and plant secondary metabolites which exhibited positive outcome toward growth inhibition of CRC by regulating pro-inflammatory cytokines (125, 126). It has been well understood that healthy commensals in gut microbiota such as L. casei, L. plantarum, L. bulgaricus, L. acidophilus, and Bifidobacterium longum can inactivate carcinogens or mutagens, alter cell differentiation and induce immunomodulatory effects toward growth inhibition of cancer cells (127). Several preclinical and clinical studies demonstrated that prebiotics, probiotics, and postbiotics can improve the immune response such as stimulation of cytokines, viz., IL-6, IL-17, and IL-23, and the downregulation of induction of pro-inflammatory Th17 cells (128). Recently, Yan Li et al. showed that the expression of GPR109A was increased and tumor counts were decreased when postbiotic butyrate got elevated in colon polyposis-bearing mice treated with prebiotic (129). The detailed effect of immunomodulatory nutraceuticals on CRC has been depicted in Figure 5 and Table 2.

Atherosclerosis is elucidated as an accumulation of cholesterol and conscript of macrophages into artery walls yielding plaques (130). As mentioned in the previous section, gut dysbiosis has been proposed to be directly associated with acute or chronic dysfunctions of atherosclerosis in the host. Intriguingly, in the last two decades, a number of nutraceuticals have shown their potential toward the management of atherosclerosis (131, 132). Much to our interest, preclinical and clinical evidences have been accumulated for their immunomodulatory role in the disease management as well. For instance, curcumin inhibited the production of IL-8, MIP-1α, MCP-1, IL-1β, and TNF-α by LPS-stimulated on human peripheral blood monocytes and alveolar macrophages. It ameliorates experimental autoimmune myocarditis (EAM) by reduced the inflammation in inflammatory macrophages and polarized M0 and M1 macrophage to M3 phenotype (133, 134). In addition, other groups also revealed that phytochemicals such as Terminalia arjuna extract had a prominent effect on the management of atherosclerosis. For example, in 2009, Halder et al. reported that T. arjuna possesses anti-inflammatory potential against some phlogistic agents as well as antinociceptive activity plausibly mediated via opioid receptors (135, 136). Similarly, Da Yeon Lee et al. (137), demonstrated that Allicin minimized inflammatory cytokines expression in murine such as IL-6, IL-1β, and TNF-α in macrophages stimulated with LPS (138). It was also demonstrated that hydroxytyrosol has played a major role toward diminishing cytokines IL-12 and IL-23 and Th1 and Th17 activation inhibiting atherosclerosis progression (139, 140). Similarly, in Qiang Wan et al. demonstrated that Berberine has decreased serum levels of IL-6 and TNF-α, which played a key role in pathogenesis of atherosclerosis (141). Interestingly, green tea extract increased the production of nitric oxide leading to enhanced vasodilation. Besides that, flavanols exhibited vasodilation plus lessened circulating oxLDL levels after 5 weeks (128). Moreover, prebiotics, probiotics, and postbiotics (SCFAs) are showing promising results toward the homeostasis of gut microbiota which is leading to counter the onset of atherosclerosis. For example, Lactobacilli have shown immunomodulatory effects against atherogenesis such as enhancement of the activity of Tregs, suppression of Th1, Th17, modification of Th1/Th2 ratio, influencing the subsets ratio of M1/M2 macrophages (142, 143). Few other groups reported that Mediterranean diet, antioxidant phytonutrient like coenzyme Q10, bioactive compounds like vitamins D, E, A and C, polyunsaturated fatty acids (ω-3 and ω-6), etc. are showed prominent effects for management of CVD (131, 144, 145). Taken together, immunomodulatory nutraceuticals can be used alone or concurrent with other pharmaceutical treatment modalities to prevent and manage atherosclerosis and to ameliorate the QoL of the patients.

Diabetes mellitus (DM) is a metabolic disease, which takes its origin from several genetic and environmental factors and characterized by insulin resistance or impaired production of insulin hormone from pancreatic β-cell, which creates an enormous health burden with micro as well as macrovascular complications. As reported by International Diabetes Federation in 2019, diabetic population was estimated to be 463 million and it was predicted to increase up to 700 million by 2045 (146). As mentioned in the previous section, alteration in gut microbial composition can largely contribute to the onset of the disease. Herein, we aim to summarize some immunomodulatory nutraceuticals including botanicals and probiotics, which can help in the management of diabetes. In 2012, Toshihiro Miura et al. reported that Lagerstroemia speciosa L., a rich source of corosolic acid as well as ellagitannins, was responsible for blocking the activation of NF-κB in a dose- and time-dependent manner in H9c2 cell line, which modulated anti-inflammatory action resulting in inhibition of diabetes-induced cardiomyocyte hypertrophy (147, 148). Similarly, other research groups (Sneha J. Anarthe et al. and Neelam Makare et al.) demonstrated that 500 mg/kg of Trigonella foenum-graecum increased the population of lymphocytes and T cell (149–151). Bitter melon, α-lipoic acid, dioscorea, allium sativum, and amaranthus have also shown positive antidiabetic immunomodulatory effects (152–156). In Bahare Salehi et al. reported that α-lipoic acid has the potential to be used for the management of diabetes and other NCDs including Alzheimer (157). In addition, Giuseppe Derosa et al. recommended that L-carnitine, α-lipoic acid, berberine, and ω-3 fatty acids might be useful toward the management of diabetes (158). Probiotics (bifidobacteria, lactobacilli, and Streptococcus thermophilus) have been demonstrated to be a powerful arsenal to combat central components of metabolic syndrome, like T2D (159). The detailed immunomodulatory effects of the nutraceuticals toward the inhibition of diabetes are summarized in Table 2 and Figure 5.

Osteoporosis, mostly afflicting postmenopausal women, is a bone metabolic disorder characterized by bone loss leading to an enhanced risk of fracture (110). As reported by Jing Yan et al. in resident microbes promote bone formation and prolonged exposure results in net skeletal growth. Hormone IGF-1, produced by microbiota, promotes bone development and remodeling (160). Other groups also demonstrated that gut microbiota played a key role in bone homeostasis, regulated bone metabolism through various pathways, endocrine system and through immune system, and promote on calcium balance (110, 161). Importantly, with a continuous accumulation of knowledge, it was disclosed that the “brain–gut” axis may be a potential target for the bone, which affects the onset and propagation of osteoporosis. Yuan-Wei Zhang et al. demonstrated that the monitoring of TNF⁺ T and Th17 inflammatory cells in the bone marrow improved the overall inflammatory state. It may be called the “brain-gut–bone” axis (162). Accumulated preclinical evidence also account for the nutraceuticals playing a potential role in the management of bone loss past menopause. Some phyto-nutraceutical compound showed positive results against osteoporosis. For instance, in 2021, Tharakan and co-workers reported a positive immunomodulatory effect of Withania somnifera extract during preclinical studies which significantly increased the production of cytokines IFN-γ, IL-4, and CD45+, CD3+, CD4+, CD8+, and CD19+ NK cells (163). Moreover, Zaffar Azam et al. recently reported that guggul extract, arjuna, coriolus versicolor, and Punica granatum showed a promising immunomodulatory effect for the management of bone health (164). Similarly (165, 166) reported that probiotics and prebiotics can help to preserve gut barrier integrity, protect against pathogenic microorganisms, and promote alteration of CD4+ T cell activation, which can modulate osteoclastogenic cytokine production (165, 166). A research group demonstrated that vitamin D has played some role in the prevention and management of osteoporosis via regulating calcium–phosphorus homeostasis controlling Treg differentiation, reducing Th17 cell response, and inflammatory cytokines secretion (167, 168). The details immunomodulatory effect is depicted in below Figure 5 and Table 2.

Polycystic ovarian syndrome (PCOS) is a gynecologic endocrine metabolic disease, particularly affecting women of reproductive age (111). As evident from prior scientific research, gut microbiota can influence the pathogenesis and clinical manifestations of PCOS (84). Recently, Fang-fang He et al. reported that gut dysbiosis occurs in PCOS animal models and patients with PCOS which hint at an apparently ambiguous role in the prevalence of Prevotellaceae (169). To our intrigue, other nutraceutical compounds have also shown their potential toward the management of PCOS. For example, probiotics and prebiotics (Lactobacillus casei, Bifidobacterium lactis, Lactobacillus plantarum, Lactobacillus rhamnosus, oligosaccharides, inulin) have shown a reduction in inflammatory cytokines (TNF-α and IL-17a) in patients with PCOS as reported by Gamze Yurtdaş et al. (111, 170). Similarly, other research groups (Bilal Bin-Hafeez et al. and Sneha J. Anarthe et al.) demonstrated a dose-dependent immunomodulatory activity of methanolic extract of fenugreek (149, 150). It has also been demonstrated that phytonutrients such as ashwagandha, amla, apigenin, and cinnamon bark extract furnish promising immunomodulatory effects for the management of PCOS, the details are summarized in Table 2 (171, 172). Moreover, in Kuniaki Ota et al. demonstrated that vitamin D has shown an immunomodulatory effect inhibiting the proliferation of Th1 cells and limit their cytokine production, such as IFN-γ, IL-2, and TNF-α. Some contradictory behavior of vitamin D has also been recorded (173, 174). In summary, immunomodulatory nutritional intervention can be used alone to prevent and manage PCOS or concurrent with other pharmaceutical treatment modalities to ameliorate the quality of life of the patients.

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of mortality and morbidity all over the world. The prevalence of NAFLD is projected in 2020 to increase up to 56% in the next 10 years (175). It is majorly caused by an accretion of fatty acid content greater than 5% of liver weight (176). Moreover, gut microbiome, its metabolites and their interactions with the immune system - together entails the pathogenesis of NAFLD and hepatocellular carcinoma (HCC) via gut–liver axis (177). Herein, we highlight some nutraceuticals, vitamins, prebiotics, and probiotic supplements, which showed positive outcome in the management of NAFLD in few preclinical and clinical settings. For instance, in Annalisa Curcio et al. demonstrated that Silybum marianum, having antioxidant and anti-inflammatory activity and comprising ∼70–80% of silymarin with a mixture of flavonolignans and silybin, improved steatosis and liver enzymes with patients with NAFLD (178). Similarly, other research groups showed that gut microbiota–derived tryptophan metabolites (I3A) weakened the expression of TNF-α, IL-1β, and MCP-1 on macrophages exposed to palmitate and lipopolysaccharide (179). In addition, probiotics/synbiotics are used as supportive supplement diets to reduce inflammation, hepatic steatosis, and liver stiffness as shown in meta-analysis (180, 181). Importantly, in 2017, Kelishadi and colleagues demonstrated that a probiotic blend containing Bifidobacterium lactis (DSMZ 32269), Lactobacillus acidophilus (ATCC B3208), Lactobacillus rhamnosus (DSMZ 21690), and Bifidobacterium bifidum (ATCC SD6576) had shown a positive result after 12 weeks of treatment on patients with pediatric NAFLD along with reduced liver injury compared to placebo treatment (180–182). Immunomodulatory effects of various nutraceuticals for the management of NAFLD are summarized in below Table 2.

Though obesity cannot strictly be stated as NCD, it is a well-known risk factor that can beget several metabolic disorders such as CVD and T2DM. It is proven that certain gut bacterial genera are associated with obesity, making microbiome modulation an attractive tool for its management. In Aline Corado Gomes et al. demonstrated various molecular patterns that lead together to obesity, such as immune system, lipid metabolism, satiety hormones, nutrient metabolism, and microbiota–adipose tissue axis (183). Thus, maintaining homeostasis and attenuation of the exaggerated inflammatory reaction owing to dysbiosis is required in order to prohibit the onset of obesity which makes probiotics a therapeutic modality against the disorder. For example, Lactobacillus gasseri SBT2055, Bifidobacterium L66, and Bifidobacterium adolescentis drew attention as they altered the composition of gut microbiota and affected food intake, appetite, body weight, body composition, and metabolic functions involving GI pathways (184). A few other groups also evaluated the effects of prebiotics on obesity. For instance, prebiotic-fed mice showed a low profile of several pro-inflammatory cytokines and diminished hepatic expression of inflammatory and oxidative stress markers that could maintain gut homeostasis and control obesity (185–188). Phytonutrients have also shown some promise in obesity management. As reported by Shiva Ganjali et al. in (162), curcumin showed a promising role in obesity management. When obese individuals treated with 1 g curcumin/day in a 4-week long randomized crossover trial, the mean serum IL-1β (p = 0.042), IL-4 (p = 0.008), and VEGF (p = 0.01) were found to be significantly reduced (189). Similarly, other authors recently reported that phytonutrients such as green tee, arjunarishta, fenugreek, and boswellic acid played a major role toward controlling obesity (190, 191). Table 2 elucidates the immunomodulatory effects of these ingredients.

Aging is a complex phenomenon spawned out of the interaction of environmental, genetic, and/or epigenetic events interfering with body’s functions with time. Age-related chronic disorders are progressively increasing due to the increased life expectancy in the elderly population. These can be attributed to the compositional shift in the gut microbiota which remains associated with low-grade inflammation and innate immunity activation which can trigger many metabolic dysfunctions. Therefore, gut microbiota can be considered as a target for the elderly population to reverse aging as well as inhibit metabolic ailments (117). Here, we mention the effects of some phytonutrients, prebiotics, and postbiotics supplements which have demonstrated their potential to ameliorate the gut dysbiosis and to direct toward healthy aging (192). In preclinical studies, curcumin demonstrated symptomatic reduction in some age-related diseases such as CVD, T2DM, and cancer owing to its well-known anti-inflammatory property via inhibiting NF-αB signaling (193). Other research groups have also demonstrated that Shilajit, Withaferin A, and prebiotics and probiotics can play crucial roles in the management and prevention of aging-associated immune compromise and metabolic diseases including cancer, diabetes, and obesity (194, 195). Probiotic supplementation increased NK cell and phagocytic activity, mostly effective in elderly population. It also ameliorated the detrimental effects of malnutrition on immunity in elderly people by improving their nutritional and immune status, as demonstrated by increasing levels of serum albumin and intestinal immunoglobulin A (IgA) production (196). In 2021, Xin Fang et al. demonstrated that the antiaging effects of the probiotic has been regulated intestinal microbiota and inhibited TLR4/NFκB-induced inflammation in mouse model (197). The effect of a probiotic blend of two Bifidobacterium species in a South Korean elderly (65 years) population after 12 weeks was measured to have reduced abundance of Prevotellaceae family and Eubacterium, Clostridiales, and Allisonela order which results in improved cognitive function and stress management capacity further reinforcing the significance of gut–brain axis. The details of immunomodulatory effects of various nutraceuticals on aging are depicted in Table 2.

Summarizing the above facts, it is quite palpable to decipher the mechanistic roles of the vast majority of the nutraceuticals are playing, which can be validated and translated into beneficial formulations with better efficacy.