While genetic predisposition is a major factor in the risk of developing age-related dementia, in particular Alzheimer’s disease, environmental factors, such as diet, also have an important role to play. Thanks to the 12-year follow-up of nearly 2,800 French people over 65, an Inserm research team sought to understand the impact of meals rich in sugars on the risk of developing dementia. Paving the way for a better understanding of the links between environmental and genetic risk factors, these results could help improve dementia prevention strategies.
According to the forecasts of theWHO, more than 152 million people could be affected by dementia linked to age in 2050. There is currently no treatment to cure or slow the progression of these diseases, of which the Alzheimer’s disease. It is therefore essential to identify the factors favoring their appearance and on which it would be possible to act in a preventive manner.
For several years, nutrition has been recognized as an important factor in the good aging of brain. Several animal studies have notably highlighted light the role of significant consumption of sugars – which includestarch and added sugars (sucrose, syrups glucose and of fructose) – in worsening clinical signs of Alzheimer’s disease, and in particular in the acceleration of the appearance of amyloid deposits (senile plaques) characteristic of the latter.
So far, no human study has explored a potential link between predispositions genetics, sugar consumption and risk of dementia.
Genetic and environmental factors of dementia
But if the environment plays on the onset of Alzheimer’s disease, the importance of the factors genetic is not negligible. This is particularly the case for uncomfortable APOE which comes in three forms (or alleles): E2, E3 and E4. People with the E4 allele of this gene are at increased risk of developing Alzheimer’s disease.
A research team led by Inserm researcher Sylvaine Artero within unit 1061 Neuropsychiatry: epidemiological and clinical research (Inserm / University of Montpellier) wanted to highlight the links between the occurrence of dementias (in particular Alzheimer’s disease) in humans, genetic predispositions linked to the E4 allele and consumption of sugars. The researchers analyzed 12-year data from nearly 2,800 participants in the cohort Française des Trois Cités, which since 1999 has followed nearly 10,000 French people over the age of 65. His work has been published in the journal Alzheimer’s and Dementia.
They studied the occurrence of 350 dementias linked to eating habits and more particularly their intake of glycemic load (the ability of the food to raise the blood sugar depending on the portion consumed) estimated over four meals: breakfast, lunch, afternoon tea, dinner. For participants who do not have the genotype at risk, the research team did not detect any association between the occurrence of dementia and the consumption of sugars during the four daily meals.
Sugar in the afternoon increases the risk of dementia in people who are genetically predisposed
However, in participants with the E4 allele of the APOE gene, the researchers observed an association between consumption of sugars during afternoon tea and the onset of dementia. For people with APOE4 who are used to having a snack, the risk of developing Alzheimer’s disease was increased by 2 to 3 times for each additional portion equivalent to the glycemic load of 30 grams of baguette, regardless of daily energy intake, activity physical, the presence of comorbidities or adherence to a healthy Mediterranean-style diet. On the other hand, no association of this type was revealed for the other meals of the day.
But, for what reason would the consumption of sugars have more impact during the snack for people with genetic dispositions? According to Sylvaine Artero, ” one hypothesis to consider would be the potential impact of insulin resistance – pathology involved in the diabetes type 2 and favored by the consumption of sugars – on the risk of developing dementia “
Glucose metabolism in carriers of the E4 allele
Indeed, it has already been shown in animals that carriers of the E4 allele presented a metabolism less efficient glucose. They are therefore more likely to develop insulin resistance. Foods high in sugars consumed during afternoon tea tend to be low in fat and fiber. They are consumed more quickly and without being accompanied by other types of food such as during main meals. They are therefore absorbed much faster in the blood during digestion, triggering a peak ofinsulin.
” Repeated daily, these insulin spikes could eventually lead to peripheral but also cerebral insulin resistance (in which the brain is less sensitive to insulin and less able to use glucose) via the oxidative stress and theinflammation, which would promote the development of dementias, phenomena to which the carriers of the E4 allele are more sensitive “, Specifies Sylvaine Artero.
” These results open the way to new strategies for prevention but must be confirmed by other population studies and deepened by experimental studies in order to better understand the links between the consumption of sugars, insulin resistance and the occurrence of dementias “, She concludes.
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