Ageing is inevitable marked by deterioration in the functioning of cells and tissues. All of us age but how we age and the event as such is genetically-based and greatly affected by the surrounding environment too. The outline is clear but what causes these irreversible changes remains a mystery and understanding the ageing process might help to modify its effects. Immunosenescence is the gradual decline in immune function with ageing which is affected greatly by the composition of the gut microbiota; it can also be changes in the function or proportion of leucocytes that are potential sources of inbuilt immunity to the body. Ageing or rather aged people comprise of a majority of the world population who are sometimes overloaded with diseases and infections probably due to compromised immune systems.
The gastrointestinal tract (GT) is composed of bacteria that propagate immune cell maturation. The gut microbiota safeguards the intestine against colonization by pathogen by modulating host immune response. The functioning of the gut microbiota depends on the composition of the gut and any reduction in its diversity that happens as a result of ageing is seriously linked to frailty, infection susceptibility, inflammatory disease and increased morbidity. Each of our immune systems undergo definite changes with ageing specifically related to polymorphonuclear (PMN) cell phagocytic capacity and natural killer (NK) cell function. The PMN cells that initiate immune response to infection clearly display decreased functionality in older adults. Quantity doesn’t matter everywhere and this is once again proved by the NK cells which increase in numbers in the aged adults but their signalling efficiency and cytokine production decrease resulting in a net decrease in function. So, reinstating PMN and NK cell functionality is a sure-shot way to fight age-related immune function decline.
Probiotics: The Key to the Immunity ‘Cell’
We are all smart enough to understand that each of us grow old and die but what we strive to achieve is to make the ageing process as comfortable as possible optimizing quality of life. With ageing comes the risk of osteoarthritis, dementia, emphysema and heart problems; the gut too contributes to numerous problems many of which can increase morbidity rates. The ageing gut leads to overexpression of proinflammatory cytokine IL-6 that impacts performance of the immune system and intestinal barrier function also increasing the risk of cancer development and progression. Changes in intestinal permeability results in the progress of local (celiac disease, cancer and inflammatory bowel syndrome) and systemic diseases (obesity, diabetes, heart disease, etc.) which shows that protecting the intestine and preserving its health helps to improve quality of life in ageing adults.
One of the effective means to restore immune system functioning is through dietary intervention. Dietary restriction exists as one of the most researched and promoted nongenetic intervention in the ageing process, specifically its impact on the gut microbiota composition and inflammation. Taking up a healthy lifestyle with diets customized for the aging population that includes a good share of probiotics helps in decreasing inflammation and other age-related changes. Probiotics are live microorganisms which on administering in appropriate doses shower the host with benefits. If you notice, many of the probiotic bacteria are of the intestinal type introduced into the body through foods to improve gut health. Avoiding diarrheal diseases, increasing intestinal barrier function and improving inflammatory intestinal disorder and age-related immunological functions are some of the commonest advantages of consuming probiotics but we have not explored much about the effects of probiotics on intestinal barrier and immune function. Two of the commonest bacteria found in human gut as well as food supplements include lactic acid bacteria (LAB) and bifidobacterial whose immunomodulatory properties are fully utilized in severing age-related disorders. Various human studies showed the ability of participants to fight infections following probiotic consumption. Administration of certain strains of these bacteria increased cytotoxicity of NK cells in elderly women, reduced length of winter infections compared to control group and also nutritional and immunological status of subjects.
Isoflavones, ageing and probiotic bacteria: Isoflavones found in foods such as soy offer protection against certain diseases. LAB and bifidobacteria transform naturally occurring isoflavones to their bioactive form.
Lignans, ageing and probiotic bacteria: Though lignans are one of the major phytoestrogens occupying a major part of our diet plant lignans cannot be absorbed directly and must be metabolized to enterodiol and enterolactone before being absorbed. Deglycosylation of the secoisolariciresinol diglucoside (SDG) present in the lignan extracts into secoisolariciresinol (SECO) is the first step towards the formation of enterolignans. SDG hydrolysis that’s possible due to probiotic bacteria helps in the release of SECO.
Meta-analysis of Controlled Studies to Evaluate the Effect of Probiotics on Immune Activity
Databases such as Embase and Medline were checked using certain keywords for prospective studies on PMN cell phagocytic capacity or NK cell tumoricidal activity after consumption of probiotics in healthy older adults aged 60 and above. The team came up with 459 titles and abstracts but after imposing several other restriction criteria only 17 studies were included for analysis. There was a total of 733 subjects most of whom were healthy and predominantly females. There was a total of 13 different probiotic strains that was investigated in the studies. Of the 17 studies taken into account, 10 were randomized, 12 included patient blinding, phagocytic capacity was reported in 9 studies and NK cell activity was reported in 14 studies. Results showed that:
Effect of Bifidobacterium Lactis on Immune Functionality
A dietary trial invited elderly people in which 30 (12 men and 18 women) of them aged 63-84 years enrolled. After imposing inclusion criteria such as good health, mobility and a willingness to follow trial guidelines, and exclusion criteria such as recent history of acute or chronic debilitating illness and intolerance to milk products each of the participants were given low-fat milk (LFM) low in lactose in powdered form. B. lactis strain was obtained and Lyophilized bacteria was mixed with the powder to come up with two different doses-a typical dose and a low dose. Each of the participants was randomly assigned into one of the two groups (each group contained 15 participants). The diet was packed into sachets containing either the LFM powder or the B. lactis HN019-supplemented LFM powder. All the participants consumed the entire contents of the sachet by mixing it in 200 mL of cool drinking water.
The trial was split into three stages with the first stage supplementing the subjects with unsupplemented milk twice a day, during the second stage they consumed milk supplemented with B. lactis HN019 (6 men and 9 women consumed a typical dose while 7 men and 8 women consumed a lower dose). During the third stage all of them consumed unsupplemented milk. Each of them was also enquired on their general health every time their immune measurement was taken. All of them were subjected to blood sampling four times during the trial- at week 0, at the end of week 3, at the end of week 6 and at the end of week 9.
Of the 30 participants one participant withdrew quoting dislike of the milk’s taste and other digestion-related problems. Between-group analysis showed not much difference between the low-dose and typical-dose group but there were time-dependent treatment effects within both groups. While no difference was recorded between time points 1 and 2 there was significant change recorded for immune variable between time points 1 and 2 and time point 3. While previous studies reported that dietary supplements were effective at increasing proportions of T lymphocyte subsets and enhancing NK cell functioning the present study clearly showed similar changes in cellular immunity after participants consumed the milk-based dietary supplement containing B. lactis HN019. Drinking B. lactis HN019 increased the presence of total, helper and activated T cells in the peripheral circulation and helped to significantly improve immune cells population that might facilitate health improvements in elderly. Maximum immune function due to B. lactis HN019 consumption occurred in those individuals who had poor pre-intervention immune responses revealing that B. lactis HN019 maximum benefited those with poorly functioning immune system even at a potentially low dose. B. lactis HN019 supplement is a good way to combat the effects of immunosenescence.
How Do Probiotics Stimulate the Immune System?
Probiotics deliver better health by inhibiting the growth of pathogenic bacteria. This is done by their active competition for nutrients (for growth and proliferation) which would otherwise be used by pathogens. Probiotics can withstand gastric juice and bile salt, multiply and function in the gut while some microbes that claim to be probiotics cannot withstand the acidity level of the gastric juice and bile salt. Another important trait for the probiotic to work properly is its ability to stick to epithelial cells. A study by Galdeano et al. showed that two microorganisms stick to intestinal epithelial cells (IECs) through toll-like receptors (TLRs) and mediate immune stimulation. Rather than the whole bacteria only fragments of the probiotic were internalized inside the IECs. The IECs in turn stimulate immune cells associated with the lamina propria, activate the innate response and cytokines released by T cells. There are several other studies that have shown positive effects of probiotics on reinstating intestinal barrier integrity through increased gene expression. Recently, there has been an increased interest shown over probiotic fermented milk (PFM). Fermentation helps in improving digestibility and nutritional quality of food. Probiotics also stimulate systemic immune response with an increase in specific antibiotic production.
Our eating habits and lifestyles change as we grow old and age-related changes in microbial diversity makes the elderly population at a risk of diseases and infections. Enhancing immune response by incorporating beneficial microorganisms in the gut helps these people avoid some of the age-related diseases.
Short-term Probiotic Supplementation Enhances Cellular Immune Function in Healthy Elderly: Systematic Review & Meta-analysis of Controlled Studies: https://www.sciencedirect.com/science/article/pii/S0271531718307978
Enhancement of Immunity in the Elderly by Dietary Supplementation with the Probiotic Bifidobacterium Lactis HN019: https://pdfs.semanticscholar.org/82dd/ed8dd509a95dc7a8f26ef242ec802d292156.pdf
Beneficial Effects of Probiotic Consumption on the Immune System: https://www.karger.com/Article/FullText/496426
Probiotic Bacteria for Healthier Ageing: Immunomodulation & Metabolism of Phytoestrogens: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5646295/
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