Egg consumption and protection from the risk of dementia associated with Alzheimer’s disease

 

Professor Dr. Salah Mahdi Hassan

Consultant and expert in poultry health and production

 

Dementia is typically defined as a progressive cognitive decline affecting multiple cognitive domains leading to a decline in independence and daily functioning. Alzheimer’s disease (AD) is the most common cause of dementia, accounting for 60-70% of cases.

 

The prevalence of dementia varies across geographic regions, although it is generally increasing steadily due to population ageing. It currently affects the lives of approximately 50 million people worldwide, and this number is expected to rise to 152 million by 2050. There is currently no effective cure for dementia and therefore primary prevention is the most effective strategy to reduce the incidence of the disease.

Eggs are of particular nutritional importance because they are rich in essential amino acids, unsaturated fatty acids, all B vitamins, folate, fat-soluble vitamins, and minerals, such as phosphorus, selenium, iron, and iodine, as well as zinc. Eggs are also a widely available source of bioactive compounds, such as choline, lutein, zeaxanthin, and other essential nutrients, which may have a positive effect on health, especially on cognition.

On the other hand, egg yolk is a major source of dietary cholesterol. While hypercholesterolemia is a risk factor for neurodegenerative diseases, the cholesterol in eggs is not well absorbed and therefore does not have a major effect on blood levels. A large number of prospective scientific studies have indicated, after a recent comprehensive analysis, that there is no association between egg consumption and many health conditions, such as cancer, cardiovascular disease, and metabolic diseases (see research no. 1).

 

One of the most important known facts is that egg components may have potential protective effects on the nervous system. Accordingly, scientific research was conducted in Spain in 2022 on the relationship between egg consumption and the risk of dementia in Mediterranean populations (Research – No. 2).

This study was conducted in 3 centers of the European Prospective Investigation into Cancer and Nutrition (EPIC), the Spanish Dementia Cohort, and included 25,015 participants aged 30-70 years who were enrolled in the study during 1992-1996 and followed up for an average period of 21.5 years. The results obtained from this study were the diagnosis of 774 cases of dementia, and of these cases, 518 cases of Alzheimer’s disease were diagnosed. Data on egg consumption were in the form of a questionnaire about the participants’ dietary program followed when they joined the study. After statistical analysis of the data, no relationship or association was observed between egg consumption and the occurrence of dementia, as well as the same result for Alzheimer’s disease.

After dividing the participants into three levels of the relative Mediterranean diet (rMED) score, which is a scale based on (8-9 points) to determine the level of adherence to the diet (nutritionovereasy.com/2014/05/calculate-your-mediterranean-diet-score/). The study showed that there is an inverse relationship between egg consumption and the risk of developing dementia and Alzheimer’s disease, especially in individuals who are less committed to the rMED diet. While this relationship was not observed in individuals who are more committed or at an average level of adherence to the diet.

 

A previous study in India conducted in 2012 noted an inverse relationship between egg consumption and cognitive decline (see study No. 3), while a study conducted in Finland in 2017 found no association between egg consumption and the risk of dementia (see study No. 4).

A recent study on eggs published in the July 2024 issue of J Nutr suggests a significant association between egg consumption and a reduced risk of Alzheimer’s disease in older adults (see Research #5). These findings come at a critical time, as the prevalence of Alzheimer’s disease is expected to rise as people age.

The study, which included community-dwelling older adults in the United States without overt dementia, from the Rush Memory and Aging Project, reported that weekly egg consumption (more than one egg per week) was associated with a 47% lower risk of developing Alzheimer’s disease. The study included 1,024 older adults with an average age of 81.4 years. Participants’ dietary habits were self-reported and other dietary factors were taken into account as part of the analysis over a median follow-up period of 6.7 years. During the study period, 280 participants (27.3%) were diagnosed with Alzheimer’s disease.

The researchers reported that dietary choline was the main driver of the association between eggs and a lower risk of Alzheimer’s disease, accounting for 39% of the association. One large egg contains 150 milligrams of choline, providing 25% of the recommended daily value. Choline is an essential nutrient in the human diet and is important for the normal functioning of all cells. Thus, the great potential of choline to act as a nutritional hub for human performance. There are several mechanisms by which choline acts as a hub:

1- Acetylcholine synthesis is affected by the availability of choline. Acetylcholine is an important neurotransmitter that controls various nerve functions such as memory and muscle control.

2- Choline-phospholipids are very important structural components of cells and are essential for the processing of dietary fats. Moreover, researchers are beginning to realize that choline-phospholipids also act as signal transducers from the outer part of cells to the nucleus. This mechanism appears to be so important and widely distributed that manipulating it by changing diet is likely to be a powerful tool for improving human performance.

Choline is present in some form in all cells, most commonly as one of the choline-phospholipids phosphatidylcholine, lysophosphatidylcholine, choline plasmalogen, platelet-activating factor, or sphingomyelin. All of these forms are essential components of all membranes. The nutritional importance of choline appears to have been first established by the pioneering work on insulin when the relationship between a low-choline diet and fat infiltration in the liver was recognized. The term lipotropic was therefore coined to describe choline and other substances that prevent fat deposition in the liver.

And for a time, choline was considered an essential nutrient in the human diet due to the presence of an endogenous mechanism for the biosynthesis of the choline moiety. Furthermore, the requirement for choline is modulated by the growth rate of the individual and the complex interrelationships between choline and nutrients such as methionine, folic acid, and vitamin B12 (lipotropes). It was previously known that human cells grown in tissue culture media have an absolute requirement for choline. Subsequent studies have demonstrated the importance of choline as an essential nutrient for normal humans when methionine is not available in excess.

Eggs are one of the few commonly consumed foods that are naturally rich in choline, a nutrient that researchers are studying to better understand its role in supporting cognitive development in infants and young children and maintaining it during aging. This study adds to the growing body of evidence that dietary choices can have a significant impact on reducing the risk of Alzheimer’s disease and supporting lifelong cognitive health.

This study builds on previous research, which found that even limited egg consumption (about one egg per week) was associated with a slower rate of memory decline compared to those who did not eat eggs. However, this appears to be the first time a study has suggested a link between egg consumption and Alzheimer’s risk, highlighting the potential of simple dietary interventions to support normal brain health. This important study also seems to chime with the current US reality, where data suggests that one in 10 Americans over the age of 45 currently suffer from subjective cognitive decline, and there are reports that by 2030, the number of people aged 65 or older with Alzheimer’s dementia could rise to 12.7 million.

 

The results are encouraging but there are limitations to consider, in that Alzheimer’s dementia is a complex disorder. While the data from this study show an association with a reduced risk of Alzheimer’s dementia, they do not establish cause and effect. The study relied on self-reported dietary data, which may be contaminated with misinformation. Further research is needed to confirm these relationships in other diverse populations.

At the end of this article, I call upon my fellow researchers, doctors and specialists in neurology, to contribute their two cents in following up on such types of research to verify them or provide more accurate information that is consistent with the Iraqi societal reality.

 

 

reference

• Egg consumption and human health: an umbrella review of observational studies. Int J Food Sci Nutr.(2020) 71:325–31.
• Association Between Egg Consumption and Dementia Risk in the EPIC-Spain Dementia Cohort. Front.Nutr. 2022,9,827307.
• Lower intake of vegetables and legumes associated with cognitive decline among illiterate elderly Chinese: a 3-year cohort study. J Nutr Health Aging.(2012) 16:549–52.
• Association of dietary cholesterol and egg intakes with the risk of incident dementia or Alzheimer disease: the kuopio ischaemic heart disease risk factor study. Am J Clin Nutr.(2017) 105:476–84.
• Association of Egg Intake With Alzheimer’s Dementia Risk in Older Adults: The Rush Memory and Aging Project. J Nutr.( 2024) 154:2236-2243.