Part 2: Aging Series: Preventing Age Related Diseases

Many older adults face significant health challenges, with a life expectancy of 18.9 years at age 65 and 24.3% reporting fair or poor health (CDC, 2021-2023).

"Nutritional frailty" is a condition in vulnerable older adults characterized by significant weight and muscle loss, leading to reduced physiological reserves and increased disability risk.

A growing recognition that many older adults are both frail and obese highlights the role of nutritional challenges, influenced by social, biological and cognitive factors – all connected to the gut microbiome (Shlisky et al., 2017).

Age is also the biggest known risk factor for Alzheimer's, where the disease is affecting about one in 13 people aged 65 to 84 and one in three aged 85 and older (National Institute on Aging, 2024). As we age, the blood-brain barrier (BBB)—which protects the brain from harmful substances from the blood—becomes more permeable, allowing immune cells and molecules to enter. This breakdown often occurs before noticeable brain shrinkage or cognitive decline in Alzheimer’s disease (AD), suggesting it may be an early trigger for neurodegeneration. Chronic inflammation further weakens the BBB by damaging key cells like astrocytes, glial cells in the central nervous system, responsible for regulating the blood-brain barrier, clearing excess neurotransmitters, and supporting synapse formation. In response, these astrocytes attempt to form a secondary barrier, but in aging and AD, they shift to a pro-inflammatory state, worsening BBB damage and fueling brain inflammation. This chronic immune activation may contribute to AD progression.

Evidence shows that the gut microbiome plays a key role in brain function and may influence the development of Alzheimer's disease. While research on the gut bacterium Blautia in the context of AD has produced conflicting results, one consistent finding is Blautia’s involvement in generating GABA—a neurotransmitter where higher levels are linked to a lower risk of AD. Blautia produces secondary metabolites, with potential antibacterial and probiotic properties (López-Otín et al., 2023). Individuals with AD have reduced GABA levels compared to healthy controls, highlighting the important role gut-derived GABA may play in supporting brain health as we age.

Many of the same factors that increase the risk of Alzheimer’s disease—such as obesity (Kivipelto et al., 2005), diet, type 2 diabetes (Arvanitakis et al., 2004)—are also connected to the gut microbiome (Musso et al, 2010). Research shows that people with AD have lower gut microbial diversity, with fewer bacteria like Firmicutes and Bifidobacterium and more Bacteroidetes, that are SCFA producers. In cognitively impaired elderly individuals, pro-inflammatory gut bacteria (Escherichia/Shigella) are more abundant, while anti-inflammatory bacteria (E. rectale) are reduced—both linked to worse brain health and AD pathology (Cattaneo et al., 2017).

Prevention

Adopting healthy lifestyle habits can support brain health by reducing memory loss and slowing dementia progression. Regular physical activity, quality sleep, managing diabetes and blood pressure, preventing hearing loss, and avoiding excessive alcohol and smoking are key factors. Exercise improves overall brain function, while controlling diabetes and blood pressure protects blood vessels and prevents damage. Limiting alcohol and quitting smoking further reduce cognitive decline (CDC, 2025). Novel therapies including Fecal Microbiota Transplant (FMT) and short-chain fatty-acid/prebiotic administration are being explored in the context of treating Alzheimer’s/Dementia via animal models, potentially providing mitigation strategies to the disease (National Institute on Aging, 2023). Regular monitoring of the gut microbiome may serve as a valuable approach for early detection, even though its role as a precursor to disease is not yet fully understood.

Parkinson's disease (PD) is characterized by the loss of dopamine-producing neurons that lead to movement difficulties. This is accompanied with loss of norepinephrine-producing nerve endings that contribute to non-motor symptoms like fatigue and blood pressure fluctuations.

Parkinson’s disease (PD) is linked to changes in gut microbiota, which may contribute to early gastrointestinal symptoms like constipation before motor symptoms appear. Research has identified a microbial signature in PD, showing reduced levels of the bacterial phylum Bacteroidetes and the family Prevotellaceae, alongside increased Enterobacteriaceae. PD patients also exhibit lower concentrations of short-chain fatty acids (SCFAs), key metabolic products of gut bacteria, which may play a role in altering the enteric nervous system and contributing to gastrointestinal dysfunction (Unger et al., 2016). 

Another study shows that PD patients had lower levels of beneficial SCFA-producing, “anti-inflammatory” bacteria. Conversely, proinflammatory Proteobacteria were more abundant in PD patients. The findings suggest that dysbiosis may contribute to neuroinflammation and α-synuclein misfolding, the abnormal folding of the alpha-synuclein protein, leading to the formation of toxic aggregates in the brain, contributing to neurodegenerative processes seen in PD (Keshavarzian, 2015).  A-synuclein can even travel through the vagus nerve to enter the brain from the gut (Kim et al., 2019).

The influential Rotterdam Study assessed Parkinson's disease prevalence in an elderly population, aiming to solidify the connection between the disease and aging. The study found that PD prevalence was 1.4%, increasing with age—ranging from 0.3% in those aged 55–64, 1.0% in those aged 65–74, 3.1% in those aged 75–84, and 4.3% in those aged 85–94. About 12% of PD cases were newly detected through screening (de Rijk et al., 1995).

Prevention

Possible prevention strategies for neurodegeneration, specifically in Parkinson's disease include lifestyle changes, many that do affect the gut microbiome. Lifestyle changes and complementary therapies can support Parkinson's disease management, including a healthy diet, regular exercise, and therapies like physical, occupational, and speech therapy. Consistent monitoring of the gut microbiome could also provide a promising method for early disease detection.

Research is ongoing into the potential benefits of dietary factors, high-intensity exercise and complementary treatments like hypnosis and massage for symptom management and disease progression (National Institute of Neurological Disorders and Stroke, 2025).

Osteoporosis can be characterized by loss of bone tissue, causing the bones to become frail and more prone to fracture. The risk for developing osteoporosis increases with age, and is most common in White and Asian women (National Institute of Arthritis and Musculoskeletal and Skin Diseases [NIAMS], n.d.). 

As women age and transition into postmenopause, the loss of estrogen disrupts the natural bone remodeling process, leading to increased bone breakdown and reduced bone formation. This disruption results in a significant loss of bone density, particularly in the first several years after menopause, when some women may lose up to 20% of their bone mass. Over time, this accelerates age-related bone loss, increasing the risk of osteoporosis. The decline in estrogen also triggers higher levels of bone-resorbing cytokines, further weakening bones. Since bone loss continues at a slower rate with aging, postmenopausal women face a heightened risk of fractures (Ji & Yu, 2015). 

The health of your gut microbiome can be linked to osteoporosis, a condition that weakens bones. In a large study, researchers found that people with osteoporosis had distinct differences in their gut microbes compared to those without the condition. Certain microbes, such as Bacteroides and Oscillospira, were more common in those with osteoporosis, associated with osteoporosis and increased microbial functions related to protein breakdown and gene transcription. Other microbes, like Collinsella, linked to a lower risk of Osteoporosis, were less prevalent. These microbial differences were connected to how the body processes amino acids, which are important for bone health (Ling et al., 2021). 

Prevention

To prevent osteoporosis, adults should maintain a healthy diet rich in calcium and protein, get enough vitamin D from sunlight or food sources, stay physically active with weight-bearing and muscle-strengthening exercises, and avoid smoking and heavy drinking. Monitoring bone health and addressing risk factors early can also help, as well as regular monitoring of the gut microbiome which may serve as a tool for early detection. For older adults, additional precautions include ensuring proper nutrient intake, engaging in exercises that improve balance and muscle strength, and taking steps to prevent falls. A bone health assessment by a doctor is recommended, especially for those at higher risk (International Osteoporosis Foundation, 2025). 

The gut microbiome significantly influences aging and the development of age-related diseases, such as Alzheimer's/Dementia, Parkinson's, and osteoporosis. Maintaining gut health through proper nutrition and lifestyle choices can help mitigate risks and support overall well-being as we age. The evolving research into microbiome-based therapies holds promise for improving the quality of life in older adults.