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Lee IM, Shiroma EJ, Kamada M, Bassett DR, Matthews CE, Buring JE. Association of step volume and intensity with all-cause mortality in older women.JAMA Intern Med. 2019;179(8):1105-1112.
Draft
A prospective cohort study testing the association between physical activity, measured in steps per day, and all-cause mortality
Participant
The study cohort included 18,289 women in the Women's Health Study who wore an accelerometer while awake for seven days in 2011 and 2015. Final data analysis (n=16,741). Their average age was 72 years.
Target parameters
Deaths were determined either through family members or public records.
Key insights
During an average follow-up of 4.3 years, 504 women died. The risk of death was inversely associated with the number of steps per day. The risk of death decreased significantly as the number of daily steps increased. The women were divided into 4 quartiles according to the number of steps and intensity of effort, interpreted from the frequency of steps. Those in the first quartile averaged 2,718 steps per day; in the second quartile, 4,363 steps per day; in the third, 5,905 steps per day; and in the fourth quartile, 8,442 steps per day.
If the relative risk of death for women in the lowest quartile of steps per day is set to 1.00, the risk for each quartile decreases significantly. The risk fell to 0.51 for people in the second quartile, 0.44 in the third, and 0.33 in the fourth (P<0.01; adapted to age and wearing time). Further adjustment for potential confounders only slightly attenuated the associations to 1.00, 0.59, 0.54, and 0.42, respectively (P<0.01).
Mortality rates continued to decline as steps increased, down to about 7,500 steps per day, at which point the benefit leveled off.
The absolute rate reduction for women in the fourth quartile compared to women in the first quartile was 9.3 deaths per 1,000 person-years. For every additional 1,000 steps per day, the hazard ratio (HR) decreased by 15%. Additional adjustment for body mass index (BMI), hypertension, high cholesterol, and diabetes shifted the quartile heart rates to more closely resemble those adjusted for age and wear time only (1.00, 0.54, 0.47, 0.34;P<0.01). When adjusting for step intensity in addition to confounders, the associations were attenuated but all remained significant (HRs per quartile: 1.00, 0.68, 0.68, 0.58;P<0.01).
The biggest impact was the 41% reduction in mortality rates between women in the first and second quartiles - that is, women who walked just 2,700 steps per day compared to 4,400 steps per day. Mortality rates continued to decline as steps increased, down to about 7,500 steps per day, at which point the benefit leveled off. Step intensity (basically how fast you walked) had relatively little impact on mortality rates. The number of steps was more important than the intensity.
Clinical implications
Many of our patients are obsessed with step counting. It's more than fashionable. Fitbit sold 14 million devices between 2010 and 2018.1Most people who own a Fitbit or other pedometer are certain that their goal is to walk 10,000 steps per day, although this number is not based on evidence.
Rather, the 10,000-step goal apparently came from Yamasa, a Japanese company that in 1965 designed a pedometer called Manpo-kei, a name that translates to "10,000 step counter."2At the time, it was thought that 10,000 steps per day were necessary to reduce the risk of coronary heart disease. This was more of a marketing idea than a medical finding.
Step counting is nothing new. People have used it as a method of measuring distance since ancient times. The wordmileis of Latin origin, frommilia passumor thousands of steps.3If you could count, you could make accurate maps and know where you were. The idea of counting steps using mechanical aids goes back to da Vinci. Thomas Jefferson had a custom-made pedometer for himself when he lived in Paris and found that he took fewer steps to walk a mile in cold weather than in warm weather.4In 1788, he sent James Madison a pedometer as a gift.5
There is little evidence about how many steps people actually need to take to improve their health. A meta-analysis by Oja et al. in 2018, which examined walking intervention studies, reported improvements in cardiovascular risk factors with increasing steps.6However, the authors were not convinced that the results they examined were truly significant. In the meta-analysis of observational studies by Kelly et al. In 2014, walking and cycling were reported to be inversely related to mortality rates, but their conclusions were recorded in metabolic equivalent task (MET) hours per week.7In 2017, Stamatakis et al. reported that walking faster was also inversely related to mortality rates.8
There are a number of specific mortality studies that are worth mentioning. In 2015, Dwyer et al. reported step counts and all-cause mortality in a cohort of Tasmanians and found a linear relationship between increasing daily steps and reduced mortality risk (n = 2,576). Compared to those described as sedentary, those who took 10,000 steps per day had a 46% lower risk of mortality over the decade of follow-up. Those who increased their daily steps over the course of the study also experienced a significant reduction in mortality risk. An increase of 1,000 steps per day was associated with a 6% risk reduction.9In a British study by Jefferis et al. in older men (n=1,655) in 2018, every 1,000 steps per day was associated with a 14% reduction in mortality risk.10
Other step counting studies have reported a reduced risk of dysglycemia, a decrease in adiposity, and improved insulin sensitivity with increasing steps.11However, according to patients, changes in mortality risk generally outweigh these types of improvements.
This recent study by Lee et al. was much larger than previous research attempts, and pedometer technology became more sophisticated over time. Based on these results, the evidence suggests that the health benefits, at least in terms of mortality, level out at around 7,500 steps per day. This can be a problem because the 10,000 step goal has become so entrenched in public belief that it can only lead to your patients questioning your expertise.
Perhaps it is best to let patients continue to think that their goal is 10,000 steps, and if they admit that they only achieved 7,500 steps, then explain the evidence. The real win is getting the couch potatoes, the bottom quartile (<2,700 steps per day), to move more. While we should encourage all of our patients to walk, we should put our greatest effort where it will make the most difference.