Challenges of aging: how the digestion changes with age

Ageing is an inevitable and natural physiological process. But ageing is not just wrinkles and grey hair – all of our body’s systems undergo major structural and functional changes.

You may imagine that we’re able to resist ageing because our life expectancy has increased. It’s true that advances in science, medicine and pharmaceuticals are allowing more people to reach an advanced old age, but this does not necessarily mean that their older age is a healthy one. Many elderly people face a number of health problems and spend their last years fighting illness, which reduces their quality of life.

We’ve pointed out many times that the digestive system is key to good health. Therefore, structural and functional changes in the digestive tract during the process of ageing affect the whole body. This article will explain how the digestive tract changes over the years and what you can do to limit the negative effects of these changes.

How ageing affects the production and secretion of digestive juices

As we age, significant structural changes occur in the organs and glands that produce digestive juices such as stomach acid, bicarbonate, enzymes and saliva.

Let’s start at the beginning, in the mouth. As we age, there’s a decrease in the number of saliva-producing glands. Saliva contains enzymes that allow the initial breakdown of nutrients. The number of receptors in the mouth also decreases, which makes it more difficult to detect food and reduces saliva secretion. There are also changes in the composition of saliva, with a decrease in enzymes such as amylase and an increase in the viscosity of saliva, which can make the initial breakdown of food more difficult and affect oral health.

One of the most common problems associated with the reduced production of enzymes with age is lactose intolerance. Lactose is the main sugar in milk and dairy products, which in healthy people is broken down in the small intestine by the enzyme lactase. However, as we age, the activity of lactase decreases, causing digestive problems in about 70% of the world’s population.

Specifically, due to the lack of lactase, lactose is not digested and absorbed in the small intestine, but instead passes to the large intestine, where it acts osmotically and causes diarrhoea. In addition, it’s fermented by the gut microbiota, causing symptoms such as bloating, abdominal pain, as well as pain in the joints, headaches, reduced concentration, and so on.

Like other digestive organs, the pancreas isn’t spared from the effects of ageing. It plays an important role in the metabolism of fats, proteins and carbohydrates. After the age of 60, it gradually decreases in volume and changes structurally. The amount of secretory glands decreases, which leads to reduced production of the pancreatic enzymes and alkaline compounds needed to neutralise the contents passing from the stomach and activate the pancreatic digestive enzymes.

These changes can result in malnutrition and are frequently accompanied by diarrhoea, bloating and abdominal pain. Given that the pancreas is responsible for the synthesis of insulin, the most important hormone for the carbohydrate metabolism, problems with its function are also reflected in the regulation of blood sugar and an increased risk of type 2 diabetes.

Ageing-related changes in intestinal motility and the function of sphincter muscles

Digestion and absorption of nutrients depend on the motility of the digestive tract and the secretion of digestive juices, which are controlled by the enteric nervous system. The latter is the most complex nervous system apart from the brain and extends from the upper oesophagus to the anal sphincter, also innervating the liver, pancreas and gall bladder.

The size of the digestive tract changes over the course of a person’s life in terms of length, circumference and volume of the intestine, which in turn affects the enteric nervous system. Animal studies show that nerve degeneration starts in adulthood, as a result of increased oxidative stress and inflammatory processes.

As we age, the total number and density of enteric nerve fibres decreases, especially those that control smooth intestinal muscles and hence peristalsis, which is essential for the passage of ingested food through the digestive tract. The production and release of neurotransmitters such as acetylcholine is also altered, affecting the coordination of muscle contractions in the gut. For these reasons, the contents of the intestine may move more slowly, posing a risk of constipation.

A lower number of nerve cells can lead to a weakened capacity of the intestinal lining to repair itself, thereby increasing its permeability. The intestinal villi, through which nutrients are absorbed, become shorter, resulting in poorer uptake of nutrients and increasing the chances of nutrient deficiencies.

Recommendations for maintaining healthy brain function are also helpful in supporting the enteric nervous system. A diet rich in colourful foods and omega-3 fatty acids is neuroprotective.

Ageing entails not only a deterioration of the nervous system, but also a weakening of smooth muscle tone. This makes sphincters, which act as a kind of gateway between the various organs, less effective. A loss of tone in the anal sphincter, which is responsible for the retention of faeces, leads to increased problems with diarrhoea and possibly faecal incontinence in the elderly.

A similar problem can occur with the lower oesophageal sphincter, which prevents the contents of the stomach from flowing back into the oesophagus. A weakened tone of this sphincter increases the risk of heartburn.

Does the gut microbiota also age?

The human digestive tract is populated by thousands of microbial species, including bacteria, viruses, archaea and yeasts, which are essential for good health.

Gut microbes are involved in a number of processes such as the digestion and absorption of nutrients and minerals, biosynthesis of vitamins, development and maturation of the immune system, fermentation of fibre that humans cannot digest and the synthesis of by-products, development of the central nervous system, maintenance of muscle mass and more. In short, their role is invaluable.

The composition of the gut microbiota is unique to each person, much like a fingerprint. It’s influenced by genetics and, most importantly, by several lifestyle factors such as diet, physical activity, smoking, and the quality of sleep, as well as age.

The most important indicator of a healthy gut microbiota, as well as of overall health, is diversity. This is similar to the situation on our planet, where a greater diversity of plant and animal species correlates with a healthier ecosystem.

In children, the diversity of the microbiota increases sharply during the introduction of solid foods and up to the third year of age. After this period, it tends to remain steady through adolescence and most of adulthood, and then, after about 60 years of age, the diversity of the gut microbiota starts to decline.

The composition of the gut microbiota also changes with age. Beneficial bacteria decrease in number, while opportunistic pathogenic bacteria, which are less abundant in the young, multiply and become more prominent.

These changes have important implications for the presence and quantity of different metabolites. Changes in the composition and diversity of the gut microbiota can result in:

1. a decrease in beneficial metabolites, which can lead to compromised integrity of the gut barrier, increased permeability and reduced immune system anti-inflammatory activity,
2. an increase in harmful endotoxins that can penetrate the more permeable intestinal wall and trigger an inflammatory immune response.

We can observe that the protective mechanisms of the immune system decline with age, a process called immunosenescence, which in turn increases the incidence of chronic low-grade inflammation.

As already noted, gut microbes and their metabolites are an important factor in the regulation of the immune system. After all, the gut is the centre of the immune system, as it is home to more than 70% of immune cells. Intestinal health is therefore critical for optimal immune cell function and for maintaining the balance between inflammatory and anti-inflammatory molecules. For example, studies of centenarians have shown that people who age in a healthy way are better at regulating the inflammatory processes of ageing through anti-inflammatory mechanisms.

However, the elderly in the Western world are more susceptible to infectious diseases due to changes in the composition and diversity of the gut microbiota and the resulting weakened immune system. They are also at greater risk of non-communicable chronic diseases such as cardiovascular diseases, metabolic diseases (for example, type 2 diabetes) and neurodegenerative diseases such as dementia.

The best we can do to ensure a balanced gut microbiota and optimal functioning of the immune system is to eat a healthy diet and exercise regularly. We should also pay particular attention to adequate fibre intake, as it stimulates the production of beneficial microbial metabolites, strengthens the intestinal barrier and reduces the production of inflammatory signalling molecules.

How do hormonal changes affect digestion?

In contrast to men, women experience significant hormone fluctuations both during the course of a month and at different times of life, including pregnancy, childbirth, breastfeeding and later menopause, which all affect the health of the digestive system.

The two hormones that play a key role in the regulation of bodily functions are oestrogen and progesterone. Their levels start to fall when women enter their 40s and reach their lowest point at the end of menopause. These hormones have important anti-inflammatory effects, they slow down digestion and influence pain perception, as well as the composition and diversity of the gut microbiota.

The decrease in oestrogen and progesterone changes the composition of the gut microbiota, which becomes more similar to that of men, and there’s an increase in the permeability of the intestinal barrier. This raises the risk of microbes and their metabolites crossing from the gut into the systemic circulation, triggering the immune system and causing silent, low-grade chronic inflammation, which in turn affects other systems in the body.

Because of this, women in perimenopause and menopause often experience digestive problems such as constipation, diarrhoea and bloating for the first time in their lives.

How is muscle loss related to the efficiency of digestion?

Muscle loss is one of the most visible aspects of ageing and a significant health problem, as progressive loss of muscle mass results in a decrease in muscle function. This becomes particularly noticeable after the age of 50.

Some studies suggest that muscle loss may be linked to intestinal function. This is mainly due to impaired capacity for absorption and changes in the secretion of the digestive hormones that are important for appetite, which leads to deficiencies in the nutrients needed to maintain muscle mass.

According to recent sources, the gut microbiota also influences the amount and function of muscle through several mechanisms, such as inflammatory and anti-inflammatory processes, the metabolism of amino acids, improved utilisation of glucose and cellular respiration, among other processes.

The first tip for preventing muscle loss is to ensure sufficient intake of protein and regular strength training.

Ageing is inevitable, but by being aware of its processes and the changes that take place, and by being proactive in managing weight, eating a healthy diet, leading an active lifestyle and managing stress, everyone can make important strides towards better health and a good quality of life, however old they are.

Sources and references

Brooks CN, Wight ME, Azeez OE, Bleich RM, Zwetsloot KA. Growing old together: What we know about the influence of diet and exercise on the aging host’s gut microbiome. Front Sports Act Living. 2023 Apr 17;5:1168731. doi: 10.3389/fspor.2023.1168731. PMID: 37139301; PMCID: PMC10149677.

Huang HH, Wang TY, Yao SF, Lin PY, Chang JC, Peng LN, Chen LK, Yen DH. Gastric Mobility and Gastrointestinal Hormones in Older Patients with Sarcopenia. Nutrients. 2022 Apr 30;14(9):1897. doi: 10.3390/nu14091897. PMID: 35565864; PMCID: PMC9103579.

Löhr JM, Panic N, Vujasinovic M, Verbeke CS. The ageing pancreas: a systematic review of the evidence and analysis of the consequences. J Intern Med. 2018 May;283(5):446-460. doi: 10.1111/joim.12745. Epub 2018 Mar 23. PMID: 29474746.

Nguyen TT, Baumann P, Tüscher O, Schick S, Endres K. The Aging Enteric Nervous System. Int J Mol Sci. 2023 May 30;24(11):9471. doi: 10.3390/ijms24119471. PMID: 37298421; PMCID: PMC10253713.

Peters BA, Santoro N, Kaplan RC, Qi Q. Spotlight on the Gut Microbiome in Menopause: Current Insights. Int J Womens Health. 2022 Aug 10;14:1059-1072. doi: 10.2147/IJWH.S340491. PMID: 35983178; PMCID: PMC9379122.

Toan NK, Ahn SG. Aging-Related Metabolic Dysfunction in the Salivary Gland: A Review of the Literature. Int J Mol Sci. 2021 May 29;22(11):5835. doi: 10.3390/ijms22115835. PMID: 34072470; PMCID: PMC8198609.