Fitness vs Smoking Mortality: What the 122,007-Person Study Shows

In a Cleveland Clinic study of 122,007 adults, being below average in cardiorespiratory fitness for your age carried the same adjusted hazard ratio for death as smoking: 1.41. The least fit quarter had about five times the risk of death of the fittest 2.3%. That is the finding behind every "unfit is worse than smoking" headline, and it holds up better than most health headlines do, as long as you read it carefully.

Key takeaways

Key takeaways

1. In 122,007 Cleveland Clinic patients, below-average fitness for your age carried the same adjusted hazard ratio as smoking (1.41), and the least fit had about five times the risk of the most fit.
2. Comparing hazard ratios across risk factors is tricky: the fitness and smoking figures describe different kinds of comparison, and the study is observational.
3. A 2024 review of 199 cohorts found each 1-MET gain associated with an 11% to 17% lower risk of death from any cause.
4. One MET is your resting energy use; brisk walking is about 4.8 METs, a 10-minute mile about 9.3.
5. Estimate your fitness with the NTNU calculator first, then a timed run or walk if you are cleared and active.
6. Twelve weeks of daily easy movement plus one weekly interval session is a realistic plan for a busy executive.

This article walks through what the study measured, why comparing it with smoking needs care, what the 2024 evidence review adds, what one MET actually means in your day, how to estimate your own fitness without a lab, and a 12-week plan for a busy executive over 40. It is coaching information, not medical advice. Talk to your doctor before starting a new training plan or doing a maximal fitness test.

What did the Mandsager 2018 study find?

Kyle Mandsager and colleagues at the Cleveland Clinic published the study in JAMA Network Open in 2018. They studied 122,007 adults (mean age 53) who did a symptom-limited treadmill test at the clinic between 1991 and 2014, and followed them for a median of 8.4 years. During that time 13,637 died.

Each person's peak treadmill performance, in METs, was ranked against others of the same age and sex. That produced five groups:

• Low: below the 25th percentile
• Below average: 25th to 49th
• Above average: 50th to 74th
• High: 75th to 97.6th
• Elite: 97.7th and above

The death rates during follow-up fell at every step up the fitness ladder. Of the low group, 23.7% died. Of the elite group, 2.6% did. Those raw figures do not account for other differences between the groups, so the researchers also ran adjusted models that accounted for other risk factors, including coronary artery disease, diabetes and smoking.

After adjustment, the key hazard ratios were:

Two points in that table matter more than the smoking line. First, there was no ceiling. Elite performers did better than the high group, including people aged 70 and over and people with high blood pressure. Second, the biggest jump in risk was at the bottom. Moving out of the lowest group is where most people stand to gain the most.

Is low fitness really worse than smoking?

Strictly, the study does not say that. It says two different comparisons produced similar hazard ratios in the same model. Here is why that needs care.

The comparisons are not the same shape. The smoking hazard ratio compares people who smoke (or had a smoking history recorded) with people who do not. The fitness figure of 1.41 compares two neighbouring fitness bands, below average against above average. The low-versus-elite figure of 5.04 compares the extremes. Pick a different pair of fitness bands and you get a different number. So "fitness is five times worse than smoking" is not a fair reading, and neither is "fitness equals smoking". The defensible statement is narrower: in this group of patients, being below average for your age was associated with roughly the same increase in death risk as smoking.

Smoking was likely measured crudely. A clinic record of smoking status does not capture how much or how long someone smoked, which can understate its effect. Decades of other research show heavy smoking is extremely dangerous; this study does not overturn that.

Hazard ratios are relative. A 41% higher hazard means something very different for a 45-year-old than for a 75-year-old, because their baseline risk is different. That is why I also show the raw death percentages above.

Everyone in the study was referred for a treadmill test at a US hospital, many because a doctor had a reason to check their heart. That is not a random sample of Canadian executives.

What the study does not prove

Mandsager is observational. The authors say plainly that a retrospective design cannot show cause and effect, and that they could not separate whether fitness protects people or whether healthier people are simply fitter. Unmeasured factors such as income and education may play a part. Fitness was measured once, so the study cannot tell you what happens when someone gets fitter or less fit over time.

What gives the finding weight is that it is not alone.

What did the 2024 umbrella review add?

In 2024, Justin Lang and colleagues published an overview of the evidence in the British Journal of Sports Medicine. They combined 26 systematic reviews with meta-analyses, covering 199 unique cohort studies and more than 20.9 million observations.

The main results:

• High fitness compared with low was associated with a 53% lower risk of death from any cause (HR 0.47).
• Each 1-MET increase in fitness was associated with an 11% to 17% lower risk of death from any cause.
• High fitness was associated with a 69% lower risk of developing heart failure (HR 0.31), and each 1-MET increase with an 18% lower risk.

The authors rated the certainty of the evidence as very low to moderate, which is common for observational research. The value of this review is the breadth: the same direction holds across millions of people and many countries. For anyone over 40, the per-MET finding is the practical one. You do not need to become elite. Each single MET you add is associated with a meaningfully lower risk.

What does one MET mean in practice?

A MET (metabolic equivalent of task) is a ratio. One MET is the energy you burn sitting quietly, which works out to about 3.5 millilitres of oxygen per kilogram of body weight per minute. Something rated 5 METs costs about five times your resting rate.

The 2024 Adult Compendium of Physical Activities gives these values:

Your fitness score is your peak: the highest MET level you can reach in an all-out effort. In the Mandsager data, a man aged 50 to 59 needed to reach at least 10.0 METs to be above average for his age, and 14.0 to be elite. Below 8.2 put him in the lowest group. For women aged 50 to 59 the equivalent marks were 8.1 for above average, 13.0 for elite, and below 7.0 for low.

Picture a 52-year-old man whose peak is 8 METs. A 10-minute mile (9.3 METs) is beyond him, even briefly. Raising his peak by two METs, to 10, would move him from the lowest group to above average for his age.

Source: Mandsager et al. 2018, Table 2 (peak estimated METs on a treadmill test).

How can I estimate my VO2 max without a lab?

There are three practical ways, in order of effort.

1. A non-exercise calculator

The Norwegian University of Science and Technology's free fitness calculator estimates your VO2 max from age, sex, resting heart rate, waist or BMI, and how you exercise. It was built from treadmill tests in the HUNT study in Norway. It involves no exertion, so it is the safe place to start, and it gives you a baseline you can watch move as your resting heart rate drops.

2. A timed run, if you already run

Kenneth Cooper's 12-minute run, published in JAMA in 1968, was validated against treadmill tests in 115 US Air Force men, with a correlation of 0.897 between field result and lab VO2 max. The Cooper Institute also publishes a 1.5-mile run formula:

VO2 max (mL/kg/min) = (483 ÷ your time in minutes) + 3.5

Divide by 3.5 to get METs. A 15-minute 1.5-mile gives 35.7 mL/kg/min, or about 10.2 METs. A 12-minute time gives about 12.5 METs.

The Cooper Institute describes its run tests as meant for people who are apparently healthy and regularly active. This is a maximal effort. Talk to your doctor first, warm up for at least five minutes, walk for five to ten minutes afterwards, and stop at once if you feel chest pain, dizziness or unusual breathlessness.

3. A walking test, if you do not run

If you are inactive, carrying extra weight or get joint pain from running, the Cooper Institute recommends a walking test such as the Rockport one-mile walk instead. It is less precise but far safer as a starting point.

Smartwatches also estimate VO2 max. Use the trend rather than the absolute number.

A 12-week plan to raise your fitness

This is general guidance for a healthy adult over 40 with a full calendar, not a personal prescription. If you have a heart condition, high blood pressure, diabetes, or you have been inactive for a long time, get medical clearance first and consider supervised training.

The structure follows the 2% Solution I have taught since 2015: 15 minutes of movement every day, plus two longer sessions a week when the calendar allows. Canada's 24-hour movement guidelines (CSEP) call for at least 150 minutes a week of moderate to vigorous activity, and this plan reaches that by week 5.

Weeks 1 to 4: build the base

• Every day: 15 minutes of brisk walking, cycling or rowing at an effort where you can talk in full sentences but would rather not.
• Twice a week: one session of 30 to 40 minutes at the same easy-to-moderate effort. Walking hills counts.
• Week 1: take your baseline. Use the NTNU calculator, and if you are cleared and already active, a timed 1.5-mile run or walk. Write the number down.

Weeks 5 to 8: add intensity once a week

• Keep the daily 15 minutes.
• Replace one longer session with intervals: warm up for 10 minutes, then 4 rounds of 3 minutes hard (breathing heavily, short phrases only) with 3 minutes easy between. Cool down for 5 minutes.
• Keep the second longer session easy and stretch it to 45 minutes.

Weeks 9 to 12: progress and retest

• Stretch the hard intervals to 4 minutes, or add a fifth round. Keep one interval session a week; a second is fine only if you are sleeping well and recovering.
• Keep the long easy session at 45 to 60 minutes.
• Week 12: repeat the exact test from week 1, same route, similar weather, same time of day. Compare.

Two things make this work for executives. Put the sessions in your calendar as meetings with yourself, and pair the daily 15 minutes with something you already do: a walking call, the commute, the first thing after you drop the kids at school. And add strength work two days a week; the next numbers to track are covered in the five numbers that predict how long you keep performing.

If you want help fitting this around your calendar, book a free 20-minute call and we will set your baseline and your first four weeks together.