Can Physical Activity Improve Cognitive Performance?
Houston We Have a Problem
By the year 2050 the number of people over 60 is expected to reach 2 billion. Currently, 35.6 million people worldwide are living with dementia; by the year 2030, that number is expected to double to 75.6 million, making it a major public health concern. Mild cognitive impairment is an intermediate but debilitating stage on the spectrum from normal cognitive performance all the way to dementia. It is estimated that 60–65% of people with mild cognitive impairment will develop dementia during their lifetime. Slowing or halting this progression can have significant implications for quality of life and health care savings. If the progression to Alzheimer's disease (the most common form of dementia) could be delayed by only one year, total costs could be reduced by an estimated 113 billion American dollars by the year 2030.
Evidence suggests that physically active people have a significantly reduced risk of cognitive impairment and dementia. Across 16 studies which included 163,797 participants without dementia Hamer and Chida found that physically active participants showed a 28% reduction in risk of developing dementia and a 45% reduction in Alzheimer's disease. Anther study consiting of 89,205 adults over the age of 40 also found that higher levels of physical activity was associated with reduced risk of cognitive decline and dementia. Across another 15 studies found that physically active individuals reduced their risk of cognitive decline by 38%. Daviglus et al. and Beckett et al. also showed across 9 studies among older adults that physically active older adults reduced their risk of developing Alzheimer's disease, relative to their inactive counterparts.
Older adults without dementia can expect to have 1–2% decline of their memory centers per year, while individuals with Alzheimer's disease experience larger volume loss. Other studies have shown that increasing age is associated with lower serum and plasma levels of brain-derived neurotrophic factor (BDNF), a key growth factor involved in learning and memory. A meta-analysis by Dinoff et al. involving aerobic exercise and resistance training in 910 healthy adults of all ages revealed an overall increase in BDNF levels following exercise interventions. Neuroplasticity, the brain's ability to create and reorganize synaptic connections, appears to be an important mechanism for improved cognition with exercise among adults of all ages. A study conducted by Colcombe et al. using functional MRI revealed aerobically trained older adults demonstrated increased neural activity in the frontal and parietal regions of the brain compared to controls. Similarly, Voss et al.'s study revealed improvements in functional connectivity throughout the brain following 12 months of aerobic training in older adults. A cross-sectional study of 165 healthy older adults found that individuals with higher fitness levels had preserved brain volumes and better performance on a spatial memory task compared to those with low fitness levels.
There is no doubt that there is plenty of evidence out there validating the use of physical exercise on reducing the risk of cognitive impairment later in life. So if the literature is undeniabe, why is cognitive decline amongst the most common diseases effecting our nation? Through the next section of this article we will discuss the major known mechanisms contributing to cognitive impairment and then dive into what we can do to help combat those factors and improve cognitive performance.
What Causes Cognitive Impairment?
Inflammation
Studies of older adults and individuals with type 2 diabetes revealed that those with higher levels of inflammation had smaller regions of their memory centers in their brain compared to those with low levels of inflammation. A cross-sectional study of 3,298 older adults reported that higher inflammatory levels were associated with lower Mini-Mental State Examination scores. A longitudinal study of 3,031 healthy older adults found that those with the highest concentrations of inflammation had a 24% increased risk of developing cognitive impairment compared to individuals with low levels of inflammation. There is encouraging evidence from a recent systematic review of 13 studies that healthy sedentary adults of all ages who participate in aerobic exercise and resistance training can reduce inflammatory biomarkers. Stronger effects were found in older adults, with high-intensity aerobic exercise being the most effective in reducing inflammation. A study involving adults over 60 who participated in 16 weeks of aerobic, resistance, and neuromotor exercise (which includes balance, coordination, agility, gait, and proprioceptive training) demonstrated greater reductions in inflammatory markers and increases in peripheral BDNF in the exercise group than in the non-exercising group. Further analyses revealed that active individuals with mild cognitive impairment showed significant improvements in executive function and attention. Aerobic exercise releases anti-inflammatory substances mitigating the levels of inflammatory cytokines and ulimtatey leads to improved cognitive performance.
Vascular Health
Cardiovascular and cerebrovascular disease risk factors such as hypertension, dyslipidemia, diabetes, and hyperinsulinemia increase the risk of cognitive impairment and dementia. An observational study followed 3,381 adults for 25 years and found that elevated blood pressure and higher fasting blood glucose increased the risk of cognitive impairment and dementia later in life. Elevated blood pressure decreases blood flow and metabolism to the brain and contribute to higher rates of cognitive impairment in elderly individuals. With all that being said is there anything we can do to reverese poor cardiovascular and cerebrovascular function and improve cogntive performance? Vidoni et al. determined that changes in fitness levels mediated cognitive improvements in older adults who participated in an aerobic exercise. Brown and colleagues found a significant association between physical fitness, cerebrovascular regulation, and cognitive function in a cross-sectional study of 42 healthy older women. A study of older adults revealed that 12 weeks of aerobic training resulted in higher resting blood flow to the brain and improved immediate and delayed memory scores compared to controls. Finally, higher fitness levels among female participants of all ages were associated with improved executive function and increased cerebral oxygenation in the frontal areas of the brain compared to women with low fitness levels. Exercise training is known to enhance oxygen and glucose transport to the brain, thereby increasing cognitive performance.