Many of us question whether that forgotten fact is a "senior moment" – or something more foreboding. Dementia – a decline in thinking, memory, and learning skills, often accompanied by behavioral and social symptoms – is diagnosed in someone in the world every 4 seconds, introducing 7.7 million new cases annually. A progressive type of dementia that starts with mild memory loss, Alzheimer's disease (AD) affects the parts of the brain that control thought, memory and language. Today, AD is among the top 10 causes of death in the US, and its debilitating course of progression takes a toll on family and caregivers.
Presently, there is no known cure for AD. As such, it becomes imperative to know your risk factors so that you can prevent or delay its onset. This column reviews recent studies that suggest important considerations that may help you to be proactive in staving off AD.
US Centers for Disease Control & Prevention. Alzheimer's Disease [Web page]. http://www.cdc.gov/aging/aginginfo/alzheimers.htm. Accessed 2 July 2015.
Blood Type Linked to Cognitive Status
With aging, the amount of gray matter present in the brain declines – the extent of this reduction appears to correlate to blood type. Matteo De Marcoa and colleagues from the University of Sheffield (UK) utilized magnetic resonance imaging (MRI) to scan the brains of 189 healthy men and women, and calculated the volume of gray matter in the brain as a function of blood type. Data analysis revealed that the individuals with an O blood type had more gray matter in the posterior proportion of the cerebellum. Those with A, B, or AB blood types had smaller gray matter volumes in temporal and limbic regions of the brain, including the left hippocampus – the earliest part of the brain damaged by Alzheimer's disease. The study authors submit: "These findings identify the cerebellar tissue as a candidate for further studying ABO function, and support a general association between ABO blood type and variance in the development of the nervous system."
De Marcoa M, Venneri A. 'O' blood type is associated with larger grey-matter volumes in the cerebellum. Brain Res Bull. July 2015;116:1–6.
Low Fitness Raises Alzheimer's Risk
Mounting evidence suggests a preventive value for physical activity in the preservation of cognitive functions with age. Jenni Kulmala and colleagues from the University of Jyvaskyla (Finland) assessed data collected on 3559 men and women, average age 50 years at the study's start, enrolled in the Cardiovascular Risk Factors, Aging, and Incidence of Dementia (CAIDE) study. The data revealed that among people in their 50s, those who self-rate their level of fitness as poor were 4 times more likely to develop dementia within 30 years than those who say they have a good level of fitness. Further, the team found that the link between poor self-assessment of physical fitness and dementia was strongest among people with chronic illnesses and those who did not carry the APOE4 gene (which is thought to associate with dementia). The study authors warn: "Perceived poor physical fitness reflects a combination of biological and lifestyle-related factors that can increase dementia risk."
Kulmala J, Solomon A, Kåreholt I, et al. Association between mid- to late-life physical fitness and dementia: evidence from the CAIDE study. J Intern Med. 2014 Jan 20.
Low Vitamin D Linked to Dementia
Older men and women with lower blood levels of Vitamin D may be at increased risk of dementia and Alzheimer's disease. David J. Llewellyn and colleagues from the University of Exeter Medical School (UK) reanalyzed data from the US Cardiovascular Health Study involving 1658 elderly adults. When the study began in 1993, none of the participants had dementia, heart disease, or stroke, and all gave blood samples for analysis. In 2008, a separate group of Cardiovascular Health Study of researchers retested the samples for circulating vitamin D levels. Whereas most people in the study did have sufficient vitamin D levels in their blood samples, defined as at least 50 nanomoles of the vitamin per liter of blood (nmol/L), about 30% of people had less than that: 419 people were deficient, with more than 25 nmol/L but less than 50, and 70 people were severely deficient, with less than 25 nmol/L. By 1999, 171 people in the study did develop dementia, including 102 cases of AD. The UK team ascertained that people who were severely deficient in vitamin D at the start of the study were more than twice as likely to develop dementia in the coming years as people with sufficient levels. The study authors write: "Our results confirm that vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer disease."
Littlejohns TJ, Henley WE, Lang IA, et al. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014 Aug 6. pii: 10.1212/WNL.0000000000000755.
Chronic Sleep Disturbance May Trigger Alzheimer's Disease
People who experience chronic sleep disturbances may be at risk of developing dementia and AD at an earlier age. Domenico Praticò, professor of pharmacology and microbiology/immunology at Temple University's School of Medicine, and colleagues studied the effects of chronic sleep disturbances on a transgenic mouse model of Alzheimer's disease. The study began when the mice were approximately 6 months old – the equivalent of adult humans in their 40s. One group of mice was exposed to 12 hours of light and 12 hours of darkness, while a second group was subjected to 20 hours of light and just 4 hours of darkness, which greatly reduced their amount of sleep. At the end of the 8-week-long study period, the researchers found that the mice in the second group demonstrated significant impairment in their working and retention memory, as well as their learning ability. Examination of the animals' brains revealed no significant differences in amyloid plaque deposits between the two groups; however, the second group of mice had a significant increase in the amount of tau protein that had phosphorylated and formed tangles inside the brain's neuronal cells. "Because of the tau's abnormal phosphorylation, the sleep deprived mice had a huge disruption of this synaptic connection," said Praticò. "This disruption will eventually impair the brain's ability for learning, forming new memory and other cognitive functions, and contributes to Alzheimer's disease." The fact that the sleep-deprived mice developed the Alzheimer's brain pathology earlier than the mice that were not deprived suggests that chronic sleep disturbance acts as a trigger which accelerates pathological processes associated with dementia and AD. Praticò concluded: "We can conclude from this study that chronic sleep disturbance is an environmental risk factor for Alzheimer's disease."
Di Meco A, Joshi YB, Praticò D. Sleep deprivation impairs memory, tau metabolism, and synaptic integrity of a mouse model of Alzheimer's disease with plaques and tangles. Neurobiol Aging. Feb 15, 2014.
Cholesterol May Predict Alzheimer's Marker
A person's patterns of LDL cholesterol and HDL cholesterol may influence the levels of amyloid-beta protein present in the brain, which typifies AD. Bruce Reed and colleagues from the University of California/Davis (US) studied data collected on 74 men and women, average age 70 years, who had normal to mildly impaired cognitive function. The team studied the participants' cholesterol levels, as well as measured brain deposits of amyloid-beta protein. They found that on average, those who had higher levels of the low-density lipoprotein (LDL, "bad") cholesterol and lower levels of high-density lipoprotein (HDL, "good") cholesterol had higher levels of amyloid in the brain. Observing that "Elevated cerebral [beta-amyloid] level was associated with cholesterol fractions in a pattern analogous to that found in coronary artery disease," the study authors posit "an important role for cholesterol in [-amyloid-beta] processing."
Reed B, Villeneuve S, Mack W, DeCarli C, Chui HC, Jagust W. Associations between serum cholesterol levels and cerebral amyloidosis. JAMA Neurology. Dec. 30, 2013.
Lifestyle Factors Affect Risk
In many aspects, the anti-aging lifestyle is anti-Alzheimer's. Deborah Barnes and colleagues from the University of California, San Francisco (US), have identified seven key risk factors for which there is consistent evidence of an association with AD; namely, diabetes, midlife hypertension, midlife obesity, physical inactivity, depression, smoking, and low educational attainment. The researchers estimate that by reducing the relative risk from each of these risk factors by 10%, it will be possible to reduce the prevalence of Alzheimer's in 2050 by 8.5%, preventing 9 million cases. The study authors write: "Around a third of Alzheimer's diseases cases worldwide might be attributable to potentially modifiable risk factors. Alzheimer's disease incidence might be reduced through improved access to education and use of effective methods targeted at reducing the prevalence of vascular risk factors (eg, physical inactivity, smoking, midlife hypertension, midlife obesity, and diabetes) and depression."
Norton S, Matthews FE, Barnes DE, Yaffe K, Brayne C. Potential for primary prevention of Alzheimer's disease: an analysis of population-based data. Lancet Neurol. August 2014;13(8):788–794.
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