The world might be dominated by youngsters owing to their attitude and behavior but speaking mathematically, we are dominated by older adults. Look around and you are sure to see a greater number of older adults everywhere around you. This segment of people seems to be the fastest growing segment in the world and they outnumber kids aged under five in both developing and developed countries. From a humble 500 million this number is expected to spike up to almost 1.5 billion by 2050. Due to such growth in the global elderly population there seems to be a sharp rise in cognitive decline and dementia rates which are emerging to be one of the greatest public health problems faced by the world. Ageing is associated with memory issues and however sharp our memory skills might be during our younger years we tend to forget things, names and issues as we grow old. Its not a rarity to see our parents search for their reading glasses everywhere in the house while it is sitting right in their neck, grandmas often look around for their knitting needle while it is present right in the cloth and our grandpas keep repeatedly enquiring about their term deposits irrespective of the fact that its being handled well by their children. All these are not abnormal and I would call it part of the ageing process. Cognitive decline might include these things that are a regular part of normal ageing, mild cognitive impairment (MCI) or severe dementia with the last being the most excruciating experience by those undergoing the phase and those staying with the patient as well. Dementia rates have been steadily rising and the numbers are projected to be anywhere around 81.1 million by 2040. Dementia is a disease that not only affects the person involved but also places significant burden on the caretaker, affects the quality of life of both the individual affected and his/her families and above all, places significant burden on health care resources.
Despite such worldwide prevalence of dementia, we don’t have any cure for it until now and rely on pharmacological and non-pharmacological approaches to minimize symptoms and delay the progression of the disease. Coming up with effective preventive strategies that could delay dementia and identifying modifiable risk factors that could prevent cognitive decline and improve the lives of the elderly is the need of the hour. Diet is one of the most potential non-pharmacological approaches to ageing successfully and we do have a number of studies showing that nutrition plays a pivotal role in having a positive effect on dementia. Time and again we have seen positive data emerging on the association between nutrients such as antioxidants, folate, omega-3 and omega-6 fatty acids but not much studies have focused on the effect of dairy foods and milk in altering dementia risk. We are going to see analysis and studies that help us get a clearer picture on the impact of dairy on dementia risk.
While dementia is the last stage of cognitive disability cognitive decline is the first stage and MCI exists in between these two. Many individuals experience subjective cognitive decline (SCD) before moving on to greater cognitive impairment. SCD is a preclinical sign of Alzheimer’s and can happen before cognitive impairment.
Dementia Risk & Dairy Consumption: A Review
A database search was done based on search terms such as dairy, milk, yogurt, food, intake, consumption, cognition, cognitive decline, cognitive performance, cognitive function, cognitive state, mild cognitive impairment, Alzheimer’s, depression and mental illness. While the search resulted in 216 studies only 30 of them were relevant. But 22 papers were omitted as they were either on soy, vitamin D or milk probiotics, they did not include cognitive measures, indicated only dairy intake and survival risk or were reviews. Finally, only 8 papers suited the study purpose all of them consisting of three cross-sectional and 5 prospective studies (study duration was 3.3 years to 30 years). Six studies included both males and females, 1 study included only males and 1 study included only females with sample sizes between 449 and 4,809 in all of them. While the participants were all middle-aged to elderly people some studies employed only those above the age of 60. One cross-sectional and five prospective studies used a food frequency questionnaire to assess dietary intake while the other cross-sectional studies used a 24-hour dietary recall.
Two cross sectional and one prospective study reported benefits due to dairy consumption with respect to dementia risk. In cross-sectional studies, decreased dairy or milk intake was linked to poorer cognitive function in elderly women with no difference found in the case of men. Greater the cheese intake lower was the risk of cognitive impairment in the elderly population but 2 studies showed no link between milk intake and dementia risk. One prospective study showed that milk intake was linked to risk of vascular dementia in older age in both men and women. Three studies found a negative link between dairy and dementia risk. The CAIDE study showed that the fat intake from the milk and dairy products were linked to a greater risk of dementia, MCI, AD and other cognitive inabilities. It showed that higher fat intake was associated with increased risk of MCI and poorer cognitive function but not with dementia or AD risk. Another Australian study on elderly men showed that consumption of full-fat milk was associated with impaired cognitive function and the third study showed that increased consumption of dairy desserts and ice creams was linked with increased risk of cognitive decline among French women. In general, two studies found that whole-fat milk consumption was associated with poor mental health in elderly men whereas decreased milk intake was linked to depressive symptoms. While 3 studies suggest that dairy consumption has beneficial effects on cognitive function there are 4 studies that show that consumption of dairy products is associated with cognitive decline in the elderly which leaves us in an inconclusive state.
Effect of Dairy Consumption on the People of North America
Age-related cognitive decline is often seen in areas such as executive functioning, attention, processing speed, episodic memory and visuo-spatial functioning. Memory-related cognitive impairment increases with age affecting up to 50% adults aged 65-74 years compared to 88% of older adults aged 85 years and above. In the case of sematic and implicit memory cognitive function remains intact.
Milk, cheese and yogurt are rich sources of vitamin B12, vitamin D and alpha-lactalbumin-this results in bioactive peptides when partially hydrolyzed and in tryptophan and cysteine when fully hydrolyzed. These components are what help in cognitive function directly or indirectly. Directly, they increase the production of ‘serotonin’ which helps in mood regulation and cognitive function and also to improve deficiencies and abnormalities in older adults’ cognitive function. Indirectly, dairy components work by mediating effects on cardiometabolic health. Dairy products and milk consumption help in improving cardiovascular health by negating any risk factors linked with metabolic syndrome. This change in cardiometabolic health imparted by high dairy intake might be the primary way through which dairy products impair cognitive decline. A study was conducted on 32 participants (8 males and 24 females) whose average age was 70.59 years. Dietary feedback was taken and disappointingly only 10 participants reported consumption of the recommended amount of dairy (3 servings per day) and the remaining 22 participants had only one or two servings per day. Almost 85% of all the participants took dietary supplements, most of them took 13% saturated fats which was way above recommendations (7%) and had their cholesterol level well within recommendations (<300 mg per day). All of them had normal cognitive function and were physically fit.
Number of Dairy Product Servings & Cognitive Performance: Tests were done to find differences between those individuals consuming <3 and >3 servings of dairy per day but results showed no differences in any of the cognitive tests.
Dairy Product Nutrient Intake & Effect on Cognitive Performance: Dairy products contain saturated fats, vitamin D and calcium and the effect of these nutrients on cognitive performance was assessed. While saturated fat was negatively associated with cognitive performance there was a positive correlation between vitamin D intake and performance on three cognitive tests. Calcium in dairy products showed no positive or negative correlation with any of the cognitive tests performed. Linear regression analyses showed that none of the nutrients were predictors on any of the cognitive tests.
Nutrients from dietary intake including dairy were uniquely associated with specific cognitive functions in older men and women.
A Meta-analysis on the Impact of Dairy Intake on Dementia
Search was carried out on three different databases to pick out those studies that compared dairy consumption and its effect on cognitive function (including those in any stage of dementia and having any type of dementia). The database came up with 2407 results and after several elimination rounds only 8 articles (1 randomized control trial (RCT) and 7 prospective cohort studies) were included in the study.
RCT: Participants in the RCT were fed a low-dairy (one serving of reduced-fat dairy food everyday) diet or a high-dairy diet (four servings of reduced-fat dairy food daily) for six months followed by an alternate diet for another 6 months without any washout period. Verbal memory, processing speed, working memory, visual attention, verbal fluency, abstract reasoning, selective reasoning, executive function and psychological well-being were used to measure cognitive performance among which only backward spatial spin working memory showed significant difference between high-dairy and low-dairy diet groups.
Cohort Studies: Two studies analyzed dairy and milk intake and its effect on cognitive function among older individuals after 5-20 years of follow-up in France and US. One study analyzed milk intake using a food frequency questionnaire (FFQ) and another analyzed dairy and milk intake using a 24-h recall. Two studies analyzed the impact using tools that predict cognitive function and both of them showed mixed results. While the first study showed that higher milk intake was associated with poor memory performance the other study showed that higher milk intake was negatively associated with executive function with no effect on verbal learning, short-term memory, executive function or expressive language. One cohort study found that regular consumption of full-cream milk decreased successful mental health ageing compared to rare consumption group, two studies showed no impact of dairy or milk consumption on cognitive decline and meta-analysis results did not show significant differences in risk for cognitive decline or cognitive impairment by comparing highest milk intake to lowest intake groups.
Two studies analyzed the impact of dairy on people with Alzheimer’s disease and their results were inconsistent. One study showed that consuming milk less than twice a week was not associated with the risk of developing Alzheimer’s compared to drinking milk daily or 2-4 times a week. The other study showed that higher consumption of milk and dairy intake significantly reduced the risk of Alzheimer’s disease. Two studies analyzed the risk of vascular dementia and just like the study on Alzheimer’s the results of these were inconsistent. One study analyzed the effect of dairy consumption on all-cause dementia and showed no significant link between dairy/milk consumption and risk for developing all-cause dementia.
Overall, the evidences are inconsistent with each other and it is not enough to show that dairy and milk consumption does have an effect on cognitive decline/dementia. Still, dairy is an important food group that ought to be included in our daily meals for nutrients and good health.
Review of Dairy Consumption & Cognitive Performance in Adults: https://www.karger.com/Article/PDF/320987
The Relationship between Dairy Product Consumption & Cognitive Performance in a Group of Community-dwelling Healthy Older Adults: https://pdfs.semanticscholar.org/7c2b/39d304985a3deec6eaf11478df9df733d3b6.pdf
Role of Milk & Dairy Intake in Cognitive Function in Older Adults: https://nutritionj.biomedcentral.com/articles/10.1186/s12937-018-0387-1
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