Introduction
Distinctive types of fats, referred to as essential fatty acids (EFA) also known as polyunsaturated fatty acids (PUFA), are vital for the development of the brain in the foetus, newborns, and children. Furthermore, they are crucial for maintaining optimal brain function in adults.
To understand the importance of these EFA’s in brain development, it is helpful to have a basic understanding of brain structure and function.
The brain consists of two primary cell types: neurons and glia (see figure 1). Neurons have been the primary focus of neuroscience research for the last century due to their responsibility for the active communicative processes that characterize the brain. On the other hand, glia play a supporting role and are typically classified into three main types: astrocytes, oligodendrocytes, and microglia.
Astrocytes perform a diverse range of functions such as separating neurons from each other, removing waste products and excess neurotransmitters from the interstitial (spaces between cells) spaces between cells, modulating synaptic activity and growth, and providing neurons with nutrients for their metabolic processes.
Oligodendrocytes form the myelin sheath surrounding the axons of many neurons, which allows for faster and more efficient communication between them.
Microglia function similarly to immune cells (monocytes and macrophages) and are responsible for clearing damaged brain tissue.
Together, these various types of glial cells play a vital role in brain development and function by supporting and regulating the complex interactions between neurons that enable all brain activity.
Lipids as Signal Transmitters in the Brain
Lipids serve a variety of essential functions in the brain, including acting as signal transmitters. Many of these lipid messengers are eicosanoids, which are signaling molecules derived from PUFA.
Eicosanoids (hormone-like molecules that act locally) include prostaglandins (produced by cells lining blood vessels and other cell types), leukotrienes (produced by white blood cells and other types of cells), and thromboxanes (produced by blood platelets), which are involved in a wide range of physiological processes in the brain, including inflammation, pain perception, and neuronal signaling.
Prostaglandins, for example, are lipid signaling molecules that play a crucial role in regulating inflammation and pain perception in the brain. They are derived from arachidonic acid (AA, omega 6) and eicosapentaenoic acid (EPA, omega 3), PUFA found in high concentrations in cell membranes.
Another example of a lipid signaling molecule in the brain is endocannabinoids (‘endo’ meaning produced in the body), which are derived from AA and other fatty acids. Endocannabinoids play a vital role in regulating a wide range of physiological processes, including mood, appetite, and pain perception.
Overall, lipids play a vital role in the regulation of numerous physiological processes in the brain, including neuronal signaling, inflammation, and pain perception, with many of these functions being mediated by eicosanoids.
Polyunsaturated fatty acids in brain development
PUFA’s are essential dietary components that play a crucial role in brain development and function. (McCann & Ames, 2005). In particular, the omega-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential for proper brain development, especially during foetal and early childhood stages. DHA, in particular, is a critical component of the brain and is concentrated in areas of the brain that are responsible for memory, attention, and behaviour.
DHA is essential for proper neuronal development and function, including the formation and maintenance of synapses and the regulation of ion channels. It is particularly important during early brain development when the brain is rapidly growing and developing.
Research suggests that regular consumption of seafood or omega-3 fatty acid supplements during the later stages of pregnancy may lead to improved outcomes in terms of infant birth weight and duration of pregnancy. Specifically, these interventions have been associated with a lower risk of premature birth. (Smuts, Huang, & et al., 2003).
Traditionally, cow's milk fat with low concentrations of EFA’s was a common ingredient in infant formulas. However, a significant development in this area was the replacement of cow's milk fat with vegetable oils that provide high levels of linoleic acid (LA, the parent omega 6).
More recently, efforts have been made to increase the content of n-3 PUFA’s in infant formulas, although the ideal ratio of alpha linolenic acid (ALA, the parent omega 3) to its longer chain metabolites, such as EPA & DHA remains a topic of debate.
Preliminary evidence suggests that dietary intake of preformed very long-chain n-3 PUFAs such as EPA and DHA leads to significantly higher deposition of these acids in developing organs than when only ALA is supplied. This has led to a growing trend of adding fish oils to infant formulas.
Alzheimer’s disease and DHA
Alois Alzheimer described the symptoms and neuropathology (study of disease of nervous system tissue) of a severe form of dementia in the early 20th century, which is now the most common form of senile dementia. The disease causes memory loss, impaired language skills, confusion, disorientation, mood changes, and general intellectual impairment.
Alzheimer’s (AD) is a neurodegenerative disease and like other neurodegenerative diseases such as, Multiple Sclerosis, Huntington’s Disease, Parkinson’s Disease, is characterized by a gross loss of specific types of cells within defined regions of the nervous system, with inflammation as a common thread that binds them together.
Epidemiologic studies suggest that long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) for arthritis can have positive effects in suppressing or delaying the onset of Alzheimer’s disease, but the evidence is not conclusive (McGeer, Schulzer, and McGeer 1996).
One challenge in conducting studies to establish definitive proof is that Alzheimer’s disease progresses slowly over many years or even decades. While postmortem analysis of elderly NSAID users without dementia and age-matched non-users revealed similar levels of senile plaque and neurofibrillary tangles, the former group had notably less activated microglia surrounding the plaques (Mackenzie and Munoz 1998). (see Figure 2). Activated microglia are a marker of inflammation, and it appears that NSAIDs may be reducing the inflammation that contributes to the symptoms of Alzheimer’s disease.
Studies analyzing the intake or blood levels of n-3 long-chain-PUFA suggest that DHA plays a role in preventing AD. Cell culture and animal models provide promising mechanistic support for DHA's effectiveness in AD. Although limited, data from clinical trials indicate that DHA could benefit patients with mild AD. Nevertheless, larger, randomized clinical trials are needed for the prevention and treatment of AD. Currently, the evidence's strength is considered insufficient
Conclusion
PUFA have been shown to provide protective benefits against prevalent chronic illnesses and improve the function of critical organs. However, neural developmental milestones during the prenatal period and early years of life have a significant impact on long-term brain functional capacity, and intervention with long-chain PUFA in neurological disorders may be too late once these milestones have passed. Despite this, PUFA may still have a role in stabilizing or partially reversing such conditions.
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