Unlike the skimpy data that support the use of most nutritional supplements for
prevention/reversal of cognitive decline and dementia, with exercise we have far
better data. The studies also include both observational and clinical
intervention studies tracking measures of mental function and volumetric brain
imaging. The latter, in particular, generate “hard” findings of brain anatomy that
are especially powerful, less subject to interpretation or bias.
Exercise increases brain volume, specifically the dentate gyrus of the hippocampus,
consistent with the concept that neuronal plasticity is preserved; increases
overall white and gray matter volumes; increases brain-derived neurotrophic
factor (BDNF), with increased IGF-1 alpha with strength training; and improves
psychometric measures including memory and executive function. One pivotal
study demonstrated that exercise increased hippocampal volume by 2% over one
has also been shown to reverse mild cognitive impairment and improve some
psychometric measures in dementia, as well as reduce the likelihood of
developing either over time.
Given the expected loss of hippocampal volume of 1-2% per year, the magnitude of
increased hippocampal volume appears to be a one-to-one tradeoff: One year of
consistent exercise achieves the equivalent of one year of reversed brain
Exercise exerts its benefits through a variety of means that includes reduced insulin
resistance in the liver, muscle, and in brain tissue; reduced blood sugar and
thereby endogenous glycation; reduced inflammatory phenomena; reduced blood
pressure; and direct effects on increasing levels of brain neurotrophic factors
that cultivate neuronal richness and plasticity. For instance, one experience
demonstrated a 400% increase in blood levels of BDNF (an indirect index of
brain BDNF) in cognitively normal males exercising over 3 months. While
strength training does not raise serum BDNF, it raises levels
of another hormone with neurotrophic effects, IGF-1 alpha. In another study,
elderly non-cognitively impaired people reduced inflammatory markers,
c-reactive protein and interleukin-6 (but not TNF-alpha), by engaging in 180
minutes/week exercise. By itself, exercise can only accomplish so much in
preserving cognitive health. But, when added to the collection of other
strategies we apply, exercise amplifies the cognitive benefits of grain and
sugar elimination, vitamin D and omega-3 fatty acid supplementation, and
cultivation of bowel flora.
Exercise should therefore be a cornerstone of your cognition-preserving efforts. Given
the variety of forms of exercise and exercise intensities studied, a “magic
formula” for exercise has not yet been worked out. But the bulk of data suggest
that most benefits occur at moderate levels of exercise, e.g., walking while
maintaining a heart rate in the 90-120 beats per minutes (bpm) range or 75% of
age-predicted maximum heart rate (age-predicted max heart rate = 220 - age in
years). For a 60-year old, for example, this means a heart rate of 120 bpm.
Exercise should be sustained for at least 30 minutes 4 or more days per week.
While bouts of high-intensity exercise (e.g., Tabatas) interspersed within
lesser levels of effort have been successful in abbreviating the amount of time
required to achieve benefits such as reversing insulin resistance and allowing
modest weight loss, this has not been examined in the setting of cognitive preservation.
It is likely, however, that the time savings generated via high-intensity
exercise can still preserve the benefits on cognitive health provided by longer
duration, less intense exercise.
Strength training appears to add a modest additional benefit in preserving cognitive
health, although the evidence is limited. However, strength training provides
benefits in other areas of health (improved bone density, improved insulin
sensitivity that facilitates reduction of blood sugar and weight management,
reduced falls) and any exercise program should include some component of
A Summary of the Evidence
Ahlskog JE, Geda YE, Graff-Radford NR
et al. Physical exercise as a preventive or disease-modifying treatment of
dementia and brain aging. Mayo Clin Proc 2011 Sep; 86(9): 876–84.
Colbert LH, Visser M, Simonsick EM et
al. Physical activity, exercise, and inflammatory markers in older adults:
findings from the Health, Aging and Body Composition Study. J Am Geriatr Soc 2004
Seifert T, Brassard, Wissenberg M et al. Endurance training
enhances BDNF release from the human brain. Am J Physiol Regul Integr Comp
Physiol 2010 Feb;298(2):R372-7.
Regular mid-life aerobic exercise reduces incidence of dementia by approximately 30%:
Hamer M, Chida Y. Physical activity
and risk of neurodegenerative disease: a systematic review of prospective
evidence. Psychol Med 2009 Jan;39(1):3-11.
Women (n = 9300) who exercised at various times along their life course reduced
incidence of mild cognitive impairment by about 50%:
Middleton LE, Barnes DE, Lui LY, Yaffe
K. Physical activity over the life course and its association with cognitive
performance and impairment in old age. J Am Geriatr Soc 2010 Jul;58(7):1322-6.
Clinical intervention studies:
A large Chinese experience (n = 15,000+) demonstrating that aerobic exercise, but
not stretching or toning, reduces development of dementia by about 20% in
cognitively normal people over 6 years. Exercise involved 45 minutes per day, 7
days per week (!).
Lee AT, Richards M, Chan WC et al.
Intensity and types of physical exercise in relation to dementia risk reduction in community-living older adults. J Am Med Dir Assoc 2015 Oct 1;16(10):899.
Cognitively normal people with pre-diabetes and type 2 diabetes experienced improved
executive function, but not memory, over 6 months of aerobic exercise (45-60
minutes x 4 days/week):
Baker LD, Frank LL, Foster-Schubert K
et al. Aerobic exercise improves cognition for older adults with glucose
intolerance, a risk factor for Alzheimer’s disease. J Alzheimers Dis
6 months of aerobic exercise in cognitively normal, sedentary adults increased
white and gray matter brain volumes:
Colcombe SJ, Erickson KI, Scalf PE et
al. Aerobic exercise training increases brain volume in aging humans. J
Gerontol A Biol Sci Med Sci 2006 Nov;61(11):1166-70.
Hippocampal volume (specifically the dentate gyrus) increased by 2% over one year in people
engaged in aerobic exercise compared to a similar magnitude of loss of brain
volume in people not engaged in exercise, changes that correlated with
increased serum BDNF levels. Memory also improved:
Erickson KI, Voss MW, Prakash RS et
al. Exercise training increases size of hippocampus and improves memory. Proc
Natl Acad Sci USA 2011 Feb 15; 108(7): 3017–22.
Meta-analysis showing improved cognitive function with exercise in people with mild cognitive
Wang C, Yu JT, Wang HF et al.
Non-pharmacological interventions for patients with mild cognitive impairment:
a meta-analysis of randomized controlled trials of cognition-based and exercise
interventions. J Alzheimers Dis 2014;42(2):663-78.
A meta-analysis of intervention studies that suggests that, once established,
exercise does not impact on dementia although it can reduce depression that accompanies dementia:
Barreto PS, Demougeot L, Pillard F et
al. Exercise training for managing behavioral and psychological symptoms in
people with dementia: A systematic review and meta-analysis. Ageing Res Rev 2015
Another meta-analysis of aerobic exercise in people with dementia (Alzheimer's and
other forms) that showed improved cognitive function:
Groot C, Hooghiemstra AM, Raijmakers
PG et al. The effect of physical activity on cognitive function in patients
with dementia: A meta-analysis of randomized control trials. Ageomg Res Rev 2016
One year of walking at 60% max heart rate in non cognitively impaired people
improved MRI-measured "functional connectivity," the intensity of
neuronal interaction between various brain regions (frontal, temporal,
Voss MW, Prakash RS, Erickson KI et
al. Plasticity of brain networks in a randomized intervention trial of exercise
training in older adults. Front Aging Neurosci 2010; 2: 32
to Forum discussion.
This is another discussion in our series on preventing cognitive decline, or
reversing early cognitive dysfunction. In this conversation we're going to
emphasize the role of exercise. Exercise is a really powerful way to preserve
mental and cognitive function. Now, exercise by itself is insufficient, right?
If all you did was bike and run and lift weights — that's not enough to
prevent dementia, because if that was true, anybody who's athletic would never have
Exercise takes on its power when it's thrown into the context of the other things
we do: the diet of the Undoctored Wild-Naked-Unwashed strategies,
the replacement of vitamin D, and omega 3 fatty acids, and cultivation
of bowel flora, and then some of the other pieces we're going to add on in our
cognitive preservation program. Exercise really amplifies a lot of these effects,
and there's good science to tell
use why that is.
When you exercise, you reduce blood pressure a little bit.
Blood pressure's a big player in dementia, both Alzheimer's dementia as well as
vascular dementia (essentially dementia from mini-strokes). Blood pressure reduces
inflammation. Inflammation is a huge driver of dementia, particularly in people
with the ApoE4 genetic marker. So, exercise reduces inflammatory markers
dramatically. It's worth adding for that purpose.
Exercise also amplifies your response to insulin; reverses insulin resistance.
Insulin resistance is a key factor in causing dementia, and exercise helps
counter that, in the brain, as well as in the liver, and muscles.
Exercise also increases neurotrophic factors, that is factors that cause the
nerve system cells in your brain to grow and to connect with each other
(neuronal plasticity). You can actually change brain structure over time, with
consistent exercise efforts. One of the reasons why that happens is because
exercise increases the levels of BDNF (Brain-Derived Neurotrophic Factor), a
very potent growth factor in the brain. Now we can't measure brain BDNF
concentration very easily (because no one wants to have their brain biopsied),
but the blood levels can reflect brain levels. In one recent study, for instance,
showed a 400% increase in BDNF levels in the blood with a consistent exercise
Strength training does not seem to increase BDNF, but it seems to increase
another neurotrophic growth factor called IGF-1α, and that also adds to
these effects. In other words, there'a whole constellation of beneficial
effects of exercise that yield positive effects on preserving your cognitive
The clinical data, in humans (not just in animals, and not just in experimental
models, in humans) has for the most part borne this out. People who exercise
are protected from dementia — typically 20 to 50% less risk for
dementia, less risk for mild cognitive impairment. The key here is to
do this as early as possible, before even mild cognitive impairment sets in,
because that's where you have the most power over preventing these kinds of
If you have early cognitive decline, exercise still is beneficial. If you have
dementia established to the extent that exercise is not so helpful,
it might be helpful for boosting mood, and other beneficial effects on
health, but it may not be that helpful. The key is to start early —
not wait for dementia to seize hold on your brain.
How much exercise, and what kind?
Well, the studies are kind of all over the place. There is no magic formula
for exercise, but several patterns seem to fall out.
It appears that about 30 minutes of exercise, 4 days a week,
provides the bulk of benefits. In other words, if you exercise for 4 days
a week for 60 minutes, you don't double the benefits. You just get
a little bit more benefits. The bulk of benefits occur with very modest efforts.
Most of us, that is most of us in our 40s, 50s, 60s and 70s, only have to achieve
a heart rate of around 90 to 120 beats per minute, or to be more precise, about
60 to 75% of your age-predicted maximum heart rate. How to calculate that is
below in the text (above this transcript on the Advanced Topic page).
Which means, that a brisk walk will do it. Casual biking will do it.
Lawn work will do it. Really, any kind of moderate activity where your heart
rate goes up somewhat, and you sweat a little bit, that's enough to provide you with cognitive
benefit. You do not have to become a triathelete. You don't have to run marathons.
It just takes modest levels of physical exercise, plus you all the other benefits
of exercise, right; reductions in blood sugar and blood pressure, better mood,
anti-inflammatory effects, etc.
It is worth adding strength training, even though it doesn't increase BDNF levels,
it has other benefits, like the increase in that other neurotrophic factor,
the IGF-1α, as well as increased muscle mass gives you better control over
weight, and insulin, and blood sugar, and decreases falls, and can increase bone
mass and protect you from osteoporosis. So strength training is worth including for
a lot of reasons, and perhaps for its contribution also to maintaining cognitive health.