Twilight Zone Revisited – Exercise and brain health

Last week I admitted I no longer believe exercise is a useful weight loss tool.  Seems I stirred up a little tempest in a teapot.

So I decided I would do a little research into why exercise is crucial if we want to live a long and vibrant life.  A quick PubMed Search – aging and exercise – and I was drowning with just under 20,000 articles.  Add in review, human, and brain health, down to 66 – a much more manageable list!

My conclusion… Physical exercise is quite likely one of the most underutilized, most inexpensive and non-invasive tools available to enhance brain health.

How does exercise enhance brain health?  Spoiler alert – it’s not via weight loss!

During moderate physical exercise, blood flow is redistributed.  Blood flow to the gut, liver and kidneys decreases.  Blood flow to the skin increases to help with cooling/sweating.  Blood flow to the muscles increases up to 100 fold!  Blood flow to the brain also increases but not to the same extent as to the muscles.

From an evolutionary perspective, this makes sense.  We needed blood, which delivers oxygen, to flow to our muscles so we could make a run for it when we lived in a hostile environment.   ‘Hungry mammoth, run!’  Plus we wanted to learn and remember ‘this is where the ‘hungry mammoth lives’ so we could avoid it in the future.  We don’t need more blood to go to the kidneys because stopping for a pee when encountering a hungry mammoth could be fatal.

The exercise induced increased flow of oxygen to the brain also stimulates the expression of BDNF (brain derived neurotrophic factor) and stimulates neurogenesis (new brain cell growth) in the hippocampus – the part of the brain responsible for memory and learning.   With exercise, we learn and remember better.

BDNF has been dubbed miracle-grow for the brain by Dr John Ratey.   In his book Spark, he details the impact of exercise on the brain specifically as it pertains to learning, mental health (ADHD, anxiety and depression) and addiction concerns that plague our society.  It’s a fascinating read.  BDNF is a neuropeptide (a little protein) that helps our neurons (brain cells) sprout connecting branches as we learn something new.  The more connecting branches between our brain cells, the stronger the memory.  If those connecting branches are reinforced we remember, if they are not, we forget.

Increase exercise, increase BDNF, increase neural connection, improve your memory – what’s not to want here?

In addition, freshly oxygenated blood pumping through the dusty crevices of our brain can clear out the metabolic toxins that can make our thought processes sluggish.  Those metabolic toxins (known reactive oxygen species) are byproducts of cellular reactions required for normal brain function and contribute to neuro-inflammation.  Get the brain blood flowing and those inflammatory reactive oxygen species are flushed away.

The result?  Our mood is better, our thoughts are clearer, our stress is down and freshly inspired we are ready to tackle anything.  At least that has been my experience with a 30 – 60 minute bout of cardio.

Furthermore, and this was the kicker-convincer for me, physical activity has also been shown to delay age related cognitive decline, which is the medical term for a severe case of where-are-my-keys-forgetfulness.  What’s even more intriguing, exercise may slow, or perhaps even reverse, some of the neurodegenerative changes associated with dementia.   WHOOSH!  WHAT?!?!?

As an aging society, second only to financial insecurity, we are terrified of memory loss/loss of independence.  Dementia – Alzheimer Disease and other non-Alzheimer dementia – is one of the fastest growing irreversible scourges of the elderly.   It affects everyone.  One in three adults is afflicted, and the rest of us are their caregivers.

Moderate exercise i) improves learning and enhances memory formation; ii) decreases neuro-inflammation; iii) improves our mood; iv) delays age related cognitive decline, and v) can potentially reverse symptoms of dementia.

What is not known, yet, is how much exercise – the dose – to prescribe.

The American College of Sports Medicine 2018 Physical Activity Guidelines for Americans currently recommends:


  • 150 minutes (2.5 hours) to 300 minutes (5 hours) moderately intense or 75 minutes to 150 minutes of vigorous intensity aerobic activity or an equivalent combination of moderate to vigorous aerobic activity, spread throughout the week;
  • additional health benefits are gained by engaging in physical activity beyond 300 minutes;
  • muscle-strengthening activities of moderate or greater intensity that involve all major muscle groups on 2 or more days a week;

Older adults:

  • multi-component physical activity that includes balance training as well as aerobic and muscle strengthening activities as listed for adults.

As a recently reformed ex-fitness enthusiast, I whole heartedly agree.  Exercise is crucial if we want to live a long and vibrant life.

Do it often for your brain, not for weight loss.

Have wonderful week,
Dr Karen