Memory failure and the gradual decline of cognitive function are among the most feared aspects of growing older. We are (grudgingly) willing to accept the wrinkles on our skin, graying hair, less defined muscle tone, and the joints that don’t want to cooperate early in the morning; but we fear losing our mental abilities. Memory and cognition are core elements of establishing and maintaining communication, which is a vital aspect of relationships. Communication keeps us connected to others as we build and share memories, make decisions, and reason through life’s challenges. Dementias such as Alzheimer’s disease, mild cognitive impairment, and Parkinson’s disease are just a few conditions of cognitive impairment associated with aging, but with life-altering consequences.
One way to preserve optimal cognitive health and function is by tending to the health of the microbiome. Our knowledge of the gut-brain axis continues to grow, it brings to light the trajectory of sweeping increases in mental health problems among those of all ages, but it also provides some answers for how to curb those same challenges. Many age-related problems, including those that affect the brain, can be linked to a decline in microbial diversity and composition of the microbiome. Alternatively, by maintaining the health of the microbiome, many common age-related problems remain silent.
Studies show that the quantities of Firmicutes, Bifidobacteria, Clostridium cluster XIV, Faecalibacterium Prausnitzii, and Blautia coccoides-Eubacterium rectal are lower in elderly individuals, while Enterobacteriaceae and Bacteroidetes exist in higher numbers, compared to younger to middle-aged adults. These changes in microbial composition are associated with a decrease in general health. Aging, alone is not to blame for these changes, but rather, the combination of poorer dietary choices, increased use of medications, different living environments (more institutionalized living), and the stress or worry of aging.
One simple step toward preserving mental health as we age may be to consume more garlic. Garlic (Allium sativum) is an inexpensive, widely available botanical with the ability to positively modulate the microbiome and improve the diversity of bacterial species. In an in vitro study, the antimicrobial actions of garlic powder were shown to reduce the number of Bacteroides, while leaving the beneficial bacterial strains unharmed. Garlic acts similar to a selective antibiotic, identifying and eliminating harmful microbial strains in the gut, while ignoring the beneficial strains, which are naturally resistant to the antimicrobial effects of garlic. As the quantities of competing microbial species decline, the quantities of beneficial strains are able to naturally flourish, which improves the composition of the microbiome.
As garlic works to improve the composition of the microbiome, it indirectly encourages the production of short chain fatty acids – compounds produced by beneficial bacterial strains that serve to activate signaling between the gut and brain via the vagal nerve. These compounds also serve to maintain a strong blood-brain-barrier, which is often predisposed to becoming more permeable as we age, contributing to declining brain health. Both actions of short chain fatty acids are important for regulating neuroinflammation, which is a key element in the pathology of many age-related neurodegenerative diseases and accelerates age-related cognitive decline.
The variety of organosulfur compounds found in garlic have potent antioxidant properties. They reduce reactive oxygen species directly, but they also increase the expression of the body’s own antioxidant enzymes such as glutathione-S-transferase, which affects cognitive ability. Not only does the antioxidant activity of organosulfur compounds help reduce neuroinflammation associated with oxidative stress, but it may also enhance memory and cognitive function by increasing 5-hydroxytryptamine levels in the brain and improving brain mitochondrial function, according to animal studies. In another study, when garlic extract was given to mice with scopolamine-induced amnesia for 21 days, both learning and memory were significantly improved as a result of an enhanced antioxidant status (measured by increased glutathione levels), and by inhibiting cortical acetylcholinesterase activity.
Other studies show that the compounds in garlic can help maintain continuous neurogenesis activity throughout adult life, which is important for sustaining cognitive health and function. More specifically, garlic was shown to enhance hippocampal cell proliferation and neurogenesis which improves memory deficits and memory impairments. This achievement was evidenced by significant increases in the number of cells positive for Ki67 and DCX, which are markers for proliferating cells and neuroblasts, respectively. Additionally, garlic treatment resulted in significantly increased brain-derived neurotrophic factor (BDNF) levels, a potent factor regulating adult neurogenesis and synaptic transmission in the brain.
Garlic is a simple way to help preserve brain function in an aging population. By modulating the microbiome, it can increase short chain fatty acids to improve signaling between the gut and brain, improve the blood-brain-barrier, and protect the brain from oxidative stress and neuroinflammation. Additionally, garlic provides direct antioxidant support and encourages neurogenesis. Not only does garlic help support healthy aging, but it may aid in preserving healthy brain function.