The benefits of exercise on the body are well known, given the legion of studies showing that regular physical activity can help to keep the heart healthy, the bones strong and numerous diseases at bay. But now, researchers are also finding that exercise has a remarkable effect on the brain, too, giving us yet another reason to tackle that treadmill.
Dutch researchers have reported that aerobic physical activities that improve cardiorespiratory fitness are beneficial for cognitive function in healthy older adults (Cochrane Database Syst Rev, 2008; 2: CD005381). "This would imply," they said, "that a physically active lifestyle resulting in enhanced fitness could affect people's cognitive abilities in the future and would enable them to partially influence their mental health."
The report was a review of 11 ran-domized controlled trials conducted in the US, France and Sweden, involving a total of 670 adults aged 55 and over. Eight of the 11 studies found that aerobic exercise increased VO2 max, an indicator of respiratory endurance, by around 14 per cent. [VO2 max is the maximum amountof oxygen (O2 in mL) utilized in one minute per kg of body weight.] The improvement coincided with better mental capacity. Compared with non-exercisers, and those following a yoga- or strength-based programme, or any other intervention, the aerobic exercisers saw significant improvements in motor function, cognitive processing speed, memory, and auditory and visual attention.
The findings echo those of a number of other reviews examining the relationship between physical activity and mental function. In three recent meta-analyses, which pooled the results of several independent studies, all found physical activity to have a positive effect on cognition (Nat Rev Neurosci, 2008; 9: 58-65).
Moreover, it appears that it's not only healthy adults who can benefit, but those who already have cognitive impairment can, too-for example, those with early signs of Alzheimer's disease. One meta-analysis of more than 2000 people from 30 different trials looked solely at this population and concluded: "Exercise training increases fitness, physical function, cognitive function, and positive behaviour in people with dementia and related cognitive impairments" (Arch Phys Med Rehabil, 2004; 85: 1694-704).
Exercise early in life can also have beneficial effects on the brain. In this meta-analysis, there was a positive correlation between physical activity and cognitive performance in school-age children (4-18 years). Benefits were found for all of the categories analyzed (including perceptual skills, IQ, academic readiness, and verbal and mathematical tests), except for memory, which was not related to physical activity (Pediatr Exerc Sci, 2003; 15: 243-56).
Also, it appears that aerobic fitness in particular has a positive effect on children's brain function.
In one study, aerobic fitness was correlated with better academic performance in third- and fifth-grade students, whereas body mass index (BMI) was inversely related (J Sport Exerc Psychol, 2007; 29: 239-52). In addi-tion, greater aerobic fitness was also related to better performance on a paper-and-pencil version of the Stroop colour-word task (Med Sci Sports Exerc, 2008; 40: 166-72).
According to Dr Charles Hillman, one of the leading researchers in this field, "These findings suggest that, although physical activity might be beneficial at all stages of life, early intervention might be important for the improvement and/or mainten-ance of cognitive health and function throughout the adult lifespan" (Nat Rev Neurosci, 2008; 9: 58-65).
The mind-body connection
So, exactly what is the mechanism behind this relationship between physical activity-specifically, aerob-ic activity-and brain function? According to the lead author of the Cochrane review, Dr Maaike Ange-varen, improvements in cognition as a result of improvements in cardio-vascular fitness can be explained by increases in cerebral blood flow that lead to increased brain metabolism which, in turn, stimulates the production of neurotransmitters and the formation of new synapses.
In fact, research in animals has revealed molecular and cellular changes produced by exercise that appear to underlie the effects of physical fitness on mental perform-ance (Cochrane Database Syst Rev, 2008; 2: CD005381).
However, Dr Hillman, the lead author of the study of the third- and fifth-graders, believes that there may well be different mechanisms in play between younger and older people as a child's brain is still developing whereas the brain of an adult isn't (Nat Rev Neurosci, 2008; 9: 58-65).
Yet, a number of questions still go unanswered. What are the best varieties, intensities, frequencies and durations of exercise? Is aerobic exercise necessary for cognitive improvement, or can the same benefits be achieved with any type of physical exercise? Is it ever too late to start an exercise programme?
Despite the current gaps in the research, what is clear right now is that physical activity is beneficial across the human lifetime. So, the simple advice is: get moving!