Physical activity and the brain
How may physical activity affect brain health?
There are many studies indicating that physical activity is beneficial for the brain. This is shown in large population studies like the Framingham study where 3,714 women and men (> 60 years of age) were followed for more than a decade (1). The researchers observed that low physical activity was associated with high risk of developing dementia in old individuals, and having small volumes of hippocampus and total brain. There are also several other types of population studies showing similar beneficial effects of physical activity on the brain (2). Although there are several types of studies indicating a positive interaction between physical activity and brain health, we know relatively little about how this interaction may come about.
We know that high blood pressure, high plasma cholesterol, diabetes, poor hearing, low early age education, and high intake of drugs like alcohol may affect brain health unfavorably via several indirect mechanisms (3). This means that general health factors are probably just as important for the brain as for other organs like the heart and the blood vessels.
Important proteins released during exercise
Another possible way physical activity may affect the brain is via circulating proteins called “myokines” that are released from working muscles or other tissues during exercise. An important candidate is brain-derived neurotropic factor (BDNF). This is a protein released from certain parts of the brain, megacaryocytes (producers of blood platelets)/ blood platelets and skeletal muscles during exercise. Several other tissues like the gut also produce BDNF. BDNF is also called a neurotrophin and plays an important role in neuron survival and growth, is a neurotransmitter modulator, and participates in neuronal plasticity (capacity to make new contact points between nerve cells), which is essential for learning and memory.
Another candidate for explaining the beneficial effect of exercise on brain function is insulin-like growth factor-1 (IGF-1), which is a protein produced in several tissues like the liver, brain and skeletal muscle. IGF-1 is also an exercise-responsive protein with many similar effects to BDNF.
A third circulatory myokine of importance for brain function is colony stimulating factor-1 (CSF-1). One of the scientists in Lifebrain, Christian A. Drevon (at the University of Oslo and Vitas Ltd), has with his research group observed that intense acute as well as long-term physical activity enhance the synthesis and release of CSF-1 in skeletal muscle. There is also increased plasma concentration of CSF-1 at acute as well as after long-term exercise (4). In addition to being one of the most responsive myokines, CSF-1 seems to be important for keeping neurons and microglia (special supporter cells for neurons in the brain) intact and healthy to prevent development of dementia (5). Thus, CSF-1 is also an important candidate for explaining how exercise can promote beneficial effects on brain health including preventing dementia, improving sleep quality and mood (Figure 1).
Figure 1. Myokines (proteins from skeletal muscle) can have beneficial effects in several organs via the brain, liver, and adipose tissue. BDNF, IGF-1 and CSF-1 are myokines with positive effects on the brain, and they are all released during physical activity.