Scientists from around the world recently released encouraging evidence about the benefits of exercise — at any age.

And the new findings suggest that we gain the biggest benefits from alternating between intense and moderate exercise.

Both of two new studies focused on aerobic-type exercise, rather than resistance/strength exercise, which — as we’ve reported in the past — also yields brain and body benefits.

Together, the two new studies from Norway and Canada greatly strengthen the evidence that robust exercise delays dementia — and/or diminishes its depths.

Norwegian study's strong evidence that exercise protects aging brains
Considerable evidence suggests that anyone seeking to reduce their risk for dementia — or delay its onset — should get and stay aerobically fit.

And the results of a new study — led by Dr. Atefe Tari of the Norwegian University of Science and Technology (NTNU) — provide especially strong evidence for that idea (Tari AR et al. 2019).

Her team’s findings demand attention, because dementia has no cure, it degrades quality of life drastically, and people live only about six years after being diagnosed. About 70% percent of cases are diagnosed as Alzheimer’s disease, which typically leads to death faster than other forms of dementia.

Fortunately, as Dr. Tari said, “It is never too late to begin exercising. The average participant in our study was around 60 years old at baseline, and … those who had poor fitness … but improved it within the next decade could expect to live two years longer without dementia.

Conversely, as the Norwegian team wrote in their research paper, “Persistently low fitness is an independent risk factor for dementia and death due to dementia.”

Although this isn’t the first study to link fitness to reduced dementia risk, it’s unique because the Norwegian group measured the fitness level of participants twice, 10 years apartwhich enabled them to evaluate how changes in fitness over time are related to dementia risk.

The study was based on records from two large studies called HUNT1 and HUNT2, which began in the 1980s to 1990s and involved 30,375 people who underwent general health, aerobic fitness, and medical tests twice, about 10 years apart.

Some people were out of shape and remained in the bottom 20% of aerobic fitness for the full 10 years of the study, while the fitness of others fluctuated. The fittest minority were defined as those whose fitness status began above the 20% level and who remained relatively fit.

To determine which participants developed dementia during a 20-year follow-up period — and to determine whether fitness affected their risk for mental decline — the Norwegian team examined records from nursing homes and memory clinics. (Norway maintains detailed health records on its people, making such studies more feasible and reliable.)

They evaluated the participants’ fitness using a standard measure called “metabolic equivalent of task” or MET, which measures the rate at which — compared with sitting quietly — an exercising person expends energy (i.e., burns calories) relative to their body weight.

As Dr. Tari said, the results were quite encouraging: “If you increase your cardiorespiratory fitness from poor to good you almost halve the risk of getting dementia. You also reduce the risk of dying from or with dementia.”

Study participants who displayed poor cardio metabolic fitness when they enrolled in the HUNT studies were significantly more likely to develop dementia, compared with otherwise similar participants who had higher levels of fitness.

Specifically, the participants who started the study ranking among the 80% with the best fitness were 40% less likely to develop dementia. And the risk of developing dementia was 48% lower among participants who rose from poor to higher fitness levels during the 10-year study period.

Dr. Tari provided further detail on the anti-dementia benefits of exercise: “In our study, each increase of 1MET was associated with a 16% lower risk of getting dementia and a 10% lower risk of dementia-related death. This is an improvement that is very achievable for most people.” (1MET roughly equals the amount of energy expended while sitting.)

Of course, “observational” studies like this cannot prove cause-effect relationships, which raises two questions: 1) did low levels of fitness among some participants weaken their bodies’ ability to protect their brains from decline, or 2) did study participants with undiagnosed cognitive deficiencies find it more difficult to exercise and increase their fitness?

Fortunately, the design of their study enabled the Norwegian researchers to answer those key questions.

As Dr. Tari said, “Our study made it easy to see which came first. We estimated the fitness of the participants for the first time in the 1980s and looked for dementia cases and deaths from 1995 onwards. We have also done separate analyses where we excluded those who got dementia or died during the first few years of the follow-up period, and the results were the same.”

It’s also reasonable to ask whether people with poor fitness might also have more risk factors for dementia, such as high blood pressure, low level of education, and a family history of brain diseases.

According to Dr. Tari, that’s an unlikely explanation for their findings: “The HUNT studies give us very broad information about the health of the participants ... by adjusting the analyses for these factors, we have ruled out that they fully explain the relationship between fitness and dementia risk in our study.”

However, as she said, exercise for the brain needs to be vigorous, even if brief: “High-intensity exercise improves fitness faster than moderate exercise, and we recommend that everyone exercise to a high heart rate at least two days each week." 

And she emphasized vigor: "Regular exercise that makes you sweaty and out of breath will ensure your fitness ... good fitness for your age can delay dementia by two years and that you can also live two to three years longer after being diagnosed with dementia.”

We covered the basics of high-intensity interval training (HIIT) in 7-Minute Fitness HIIT and Fixing the Harms of a Sedentary Past, Fast.

Needless to say, it's wise to get your heart health checked before beginning high-intensity exercise.

Canadian findings echo Norwegian’s results
A few days before the Norwegian study was published, researchers at Canada’s McMaster University reported finding that high-intensity workouts improved memory in older adults.

The McMaster team found that on average, seniors who included short bursts of vigorous activity in their exercise routine enjoyed memory improvements of up to 30% — but participants who worked out moderately saw no improvement (Kovacevic A et al. 2019).

The study was led by Jennifer Heisz, an associate professor in McMaster’s Department of Kinesiology. As she said, “This work will help to inform the public on exercise prescriptions for brain health, so they know exactly what types of exercises boost memory and keep dementia at bay.”

Earlier research from Heisz’s lab that found physical inactivity raises dementia risk as much as genetics.

Her team recruited 64 sedentary but otherwise healthy older adults between the ages of 60 and 88 who were divided into three groups:

The HIIT routine included four sets of high-intensity exercise on a treadmill for four minutes, followed by a recovery period. The MICT routine consisted of one 50-minute set of moderate-intensity aerobic exercise.

Before and after the 12-week study, the participants’ memory and executive functions were measured using standard tests for those brain functions.

Importantly, the researchers used a test of “high-interference” memory, which enables us to do things such as distinguish one car from another of the same make or model. The test they used probes the newborn neurons generated by exercise, which — compared with mature neurons — are more active and enhance both formation of new brain connections and new memories. 

And the results showed that, compared to the MICT or control groups, people assigned to the HIIT group showed substantial improvements in high-interference memory.

Significantly, the researchers also found that improvements in fitness levels were linked to improvements in memory performance.

As professor Heisz said, “It’s never too late to get the brain health benefits of being physically active, but if you are starting late and want to see results fast, our research suggests you may need to increase the intensity of your exercise”. (See 7-Minute Fitness HIIT and Fixing the Harms of a Sedentary Past, Fast.)

She noted that it’s important to increase exercise intensity gradually, and to start by tailoring your routine to your current fitness level.

You can boost exercise intensity with simple changes: add hills to a daily walk or alternate between a moderate walking pace and your maximum walking pace. Then — when you’re able — alternate sprinting with speedy walking.

Of course, if you can't run or speed-walk comfortably, you can do interval-type training in a pool or on an exercise machine.


  • Kovacevic A, Fenesi B, Paolucci E, Heisz JJ. The effects of aerobic exercise intensity on memory in older adults. Appl Physiol Nutr Metab. 2019 Oct 30. doi: 10.1139/apnm-2019-0495. [Epub ahead of print]
  • Pedisic Z, Shrestha N, Kovalchik S, Stamatakis E, Liangruenrom N, Grgic J, Titze S, Biddle SJ, Bauman AE, Oja P. Is running associated with a lower risk of all-cause, cardiovascular and cancer mortality, and is the more the better? A systematic review and meta-analysis. Br J Sports Med. 2019 Nov 4. pii: bjsports-2018-100493. doi: 10.1136/bjsports-2018-100493. [Epub ahead of print] Review.
  • Tari AR, Nauman J, Zisko N, Skjellegrind HK, Bosnes I, Bergh S, Stensvold D, Selbæk G, Wisløff U. Temporal changes in cardiorespiratory fitness and risk of dementia incidence and mortality: a population-based prospective cohort study. Lancet Public Health. 2019 Nov;4(11):e565-e574. doi: 10.1016/S2468-2667(19)30183-5.