MADRID, Spain — Evidence suggests that dairy consumption is associated with better cognitive health in older adults. However, the results of a recent investigation introduce an exception to this possible link. Researchers found that high consumption of whole milk was associated with a higher rate of cognitive impairment in older adults with a high risk for cardiovascular disease.
The study was carried out by the Online Center for Biomedical Research in the Physiopathology of Obesity and Nutrition (CIBEROBN) and the Human Nutrition Unit of the Universitat Rovira i Virgili-Institut d'Investigació Sanitària Pere Virgili in Tarragona, Spain. It was part of the framework of the PREDIMED-Plus project and resulted from the collaboration of scientists from the Associated Online Center for Biomedical Research in Epidemiology and Public Health and Online Center for Biomedical Research on Diabetes and Metabolic Diseases.
Jiaqi Ni, predoctoral researcher at CIBEROBN and first author of the study, told Medscape Spanish edition that this work was conducted because the prevalence of cognitive impairment worldwide, including dementia, has increased. This rising prevalence is an increasingly important public health problem. "To this day, there are still no effective treatments available to cure cognitive disorders or slow the rate of impairment to this level. Therefore, prevention strategies targeting the modifiable risk factors, such as dietary intake and eating habits, remain a promising approach."
Regarding the research hypothesis, Ni commented that "on the one hand, previous studies have suggested that the consumption of milk and other types of dairy products plays a beneficial role in preventing age-related cognitive impairment and dementia. However, the evidence is somewhat controversial and unclear, especially when looking at consumption over time."
Likewise, "the type of dairy products according to their fat content or the state of fermentation in which these dairy products are found," was not always clear in previous research, which was a reason for the current study.
The study included 4668 participants in the PREDIMED-Plus study aged between 55 and 75 years. Participants had overweight or obesity and had metabolic syndrome, which was defined as having at least three of the following five criteria: altered blood glucose, high triglyceride levels, high blood pressure, abdominal obesity, and low high-density lipoprotein cholesterol levels. Participants completed a validated food frequency questionnaire at study baseline and an extensive battery of neuropsychological tests at study baseline and at 2 years of follow-up.
Saturated Fat Hypothesis
"The results showed a positive association between high consumption of whole milk and the rate of cognitive impairment in older adults at high risk for cardiovascular disease compared with those who consumed less milk during a 2-year follow-up period. The people who consumed the most whole milk showed cognitive impairment. However, no significant associations were observed between the consumption of low-fat milk and dairy products or with fermented (yogurt and cheese) or nonfermented (all types of milk) dairy," said Ni.
The biologic mechanism by which whole dairy products have this negative effect on cognitive function is not clear. One possibility that the researchers are considering relates to the effect of saturated fats (whole milk is rich in this type of fat) on cardiovascular risk factors, such as obesity, type 2 diabetes, hypertension, and dyslipidemia.
"These factors have been associated with an increased risk of cognitive dysfunction related to pathological vascular changes. Saturated fat has been suggested to increase low-density lipoprotein cholesterol, which negatively affects blood lipids and increases the risk of arteriosclerosis and other cardiovascular diseases," said Ni.
"Although saturated fat is one of the nutrients in dairy products that have been proposed to affect cognition, it has been suggested that the effects of this fat should be considered in the context of the total source of calories consumed and the dietary pattern. However, more studies are needed to confirm these speculations," she added.
Naiara Fernández, PhD, a nutrition expert and member of the Leadership Group of the Spanish Society of Geriatrics and Gerontology, who was not involved in the research, told Medscape that the benefit of dairy intake in Alzheimer's disease had previously been linked to its ability to inhibit inflammatory cytokines, reduce oxidative stress, and prevent beta-amyloid deposition.
"Likewise, dairy intake has been associated with the prevention of cardio- and cerebrovascular events, as it is a protective factor for the establishment of arterial hypertension and diabetes independently. These are all risk factors for the onset of cognitive impairment," Fernández added.
"Regarding the specific role of whole milk, based on the population in which the association has been seen, with a high vascular risk, it seems correct to relate the intake of milk fats, especially the content of saturated fats, with the loss of cognitive function, especially taking into account that this association is not maintained in the case of the intake of semi or skimmed dairy products," she pointed out.
Another piece of evidence produced by this investigation is that the negative effect at the cognitive level of consuming whole milk is more evident in men than in women.
"Indeed, we have seen in our results that total milk consumption was associated with cognitive impairment, at 2 years of follow-up, in men, but not in women. The different physiological features of these two populations could be related to this result, as well as anthropometric factors, lifestyle factors (smoking, physical activity, adherence to the Mediterranean diet) and different prevalences of diseases present at the beginning of the study, but more research is needed in this regard," said Ni.
Regarding the possibility of extrapolating these findings to the older population in general without cardiovascular risk, in Ni's opinion, the study's observational design makes it infeasible to determine causality. "As a certain population with these particular features has been analyzed, these results cannot be extrapolated to the general population, nor can it be determined that having a cardiovascular risk profile was decisive in these findings. However, this study allows us to provide evidence for further research on this topic."
Fernández also urged caution when transferring these results to older people and, above all, to avoid generalization. "Older people, in the context of physiological aging, and due to the comorbidity they usually present, may have specific nutritional requirements, being at greater risk of developing malnutrition and, secondarily, sarcopenia, which puts their functional autonomy at medium-long term risk," she said. "Carrying out a comprehensive geriatric assessment to analyze their needs and establish an individualized intervention plan, in which objectives are set, also in terms of prevention of cognitive deterioration, should be the way to proceed for the elderly population with and without established vascular risk."
Personalized Nutritional Guidelines
In relation to nutritional guidelines in general, and those referring to the consumption of dairy products in particular, aimed at this population group, Fernández pointed out that the consumption of three servings of dairy products daily (in the form of milk or equivalent units of its derivatives: yogurt, cheese serving, etc.) is recommended. She mentioned the need to ensure an adequate supply of calcium and vitamin D to ensure bone and muscle health.
Likewise, Fernández commented on other evidence that, in line with this investigation, links certain nutrients with cognitive health. "There are multiple studies that have linked alcohol intake with the development of dementia directly through degeneration or indirectly due to the appearance of vascular events that, in the long term, condition the establishment of cognitive impairment. Likewise, the intake of products with a high glycemic index (simple sugars, white bread) also predisposes to the loss of cognitive function, even in nondiabetic people.
"On the other hand, the scientific evidence linking dietary salt content to cardiovascular and cerebrovascular health, as well as neurodegenerative diseases, is extensive, so we should limit its use to ensure a healthy lifestyle. And likewise, reducing the intake of products high in saturated fat is known to promote sustained cognitive function over the years," said Fernández.
Fernández emphasized that to guarantee the maintenance of muscular and cognitive function in the older population, it is necessary to carry out an individualized nutritional assessment, exploring individuals' culinary habits and considering their financial capacity. "In this framework, the main general recommendations are to avoid alcohol consumption, limit the intake of salt, products rich in saturated fats and with a high glycemic index, to which the consideration of the use of low-fat dairy products (skimmed or semi-skimmed) must be added in the case of presenting a high vascular risk."
Ni stressed that cognitive impairment is a long-term process. "So, it would be interesting to continue this study, especially when we complete the 6 years of intervention of the PREDIMED-Plus project, to study at that time the associations of dairy consumption and the change in cognitive function at 6 years' follow-up, focusing the research on the significance of clinical evidence."
Ni and Fernández reported no relevant financial conflict of interest.
Follow Carla Nieto of Medscape Spanish edition on Twitter @carlanmartinez.
This article was translated from Medscape Spanish edition.
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Cite this: Does Whole Milk Speed Cognitive Decline in Older Population? - Medscape - Jul 22, 2022.