Low levels of "good" cholesterol contribute to the development of senile dementia
Scientists from the French National Institute of Health and Medical Research and the University of London, working under the guidance of Dr. Archana Singh-Manoux, studied information about a sample of 3,673 people (26.8% of them women) from the Whitehall II study and found that the reduction in the level of "good" cholesterol (lipoproteins high density, HDL) is a prognostic indicator of memory deterioration after 60 years. The purpose of the Whitehall II study, which began in 1985, is to study the state of health and factors affecting it by observing more than 10,000 civil servants working in London.
The authors defined a low level of high–density lipoproteins as less than 4 mg/ml, and a high level as 6 mg/ml or higher. They compared the lipid content in the blood and the memory state of the participants at the 5th (1996) and 7th (2002) stages of Whitehall II, when the age of the participants was 55 and 61 years, respectively.
The concentration of lipids in the blood was assessed at the end of an 8-hour fast or at least 4 hours after a light breakfast. Short-term verbal memory, the violation of which, according to the authors, is a key link in the development of senile dementia, was evaluated using a test in which participants were read 20 one- or two-syllable words at two-second intervals, after which they had to write down as many words as possible from memory for 2 minutes.
As a result , the following patterns were revealed:
– at the age of 55, low HDL increases the risk of deterioration of short-term memory by 27% compared with high levels of "good" cholesterol;
– at the age of 60, this figure increases to 53%;
– during the five years that passed between the 5th and 7th stages of the study, participants with decreasing HDL levels had a 61% decrease in their ability to remember words compared to participants with high levels of "good" cholesterol;
– there were no significant differences between men and women in the nature of the relationship between lipid levels and memory status;
– the levels of total cholesterol and triglycerides did not affect the ability to remember;
– there was no relationship between taking statins – drugs to increase HDL levels and reduce the level of low–density lipoproteins ("bad" cholesterol) - and the state of memory.
High-density lipoproteins, the high level of which reduces the risk of myocardial infarction, perform several vital functions in the body. They purify the blood from excess cholesterol, participate in the maturation of nerve synapses, as well as in the regulation of the synthesis of beta-amyloid – the main component of protein plaques contained in the brains of patients with Alzheimer's disease.
The mechanisms underlying the relationship between the level of "good" cholesterol and senile dementia are unknown. The authors suggest that HDL prevents the formation of beta-amyloid. It may also affect the state of memory by countering the development of vascular-damaging diseases such as atherosclerosis and stroke. In addition, "good" cholesterol can affect memory through its anti-inflammatory and antioxidant effects.
When conducting most of the earlier studies on the relationship between lipid levels and the state of memory in older people, scientists assessed the total cholesterol level or the level of low-density lipoproteins, high levels of which are a proven risk factor for cardiovascular diseases.
According to the results obtained by the authors, special attention should also be paid to the level of high-density lipoproteins, which is increased by regular physical activity, a decrease in total fat intake, the exclusion from the diet of fats with a high melting point containing more saturated fatty acids, and trans fats that are part of margarine, and the use of monounsaturated fats, such as olive oil, rapeseed and peanut butter.