Wearable devices such as smartphones measure a number of variables including the number of steps taken per day. Over the past several years, it has been ingrained in our culture that the goal for people whose primary activity consists of walking is 10,000 steps per day. You may be surprised to learn that the origin of this recommendation is not completely clear, and little data exists to support this number. It is not known how many daily steps are necessary for good health, and this number may actually vary considerably by age and sex. Furthermore, because steps can be taken slowly or rapidly, there is a great need for objectively measured data in this area.  

To help fill in this research gap, 18,289 women with an average age of 72 years who were enrolled in the Women’s Health Study, took part in a project that assessed physical activity. This particular study was led by Dr. I-Min Lee from the Division of Preventive Medicine at Harvard Medical School. The women were mailed an ActiGraph GT3X+ accelerometer and were asked to wear the device on their hip for seven consecutive days during their waking hours, and then return it for analysis. Only women who wore the device for at least 10 waking hours per day on four or more days (n=16,741) were included.

In addition to measuring the average number of steps taken per day, the device also measured the number of steps taken per minute throughout the day. From this data, several different daily stepping intensities were identified:

• Peak 1-minute cadence: number of steps taken for the single highest minute of the day
• Peak 30-minute cadence: average steps per minute from the 30 highest minutes of the day; the minutes did not have to be consecutive.
• Maximum 5-minute cadence: average steps per minute from the maximum number of steps recorded over any 5 continuous minutes of the day
• Stepping rate of 1 to 39 steps per minute:  incidental or sporadic steps taken
• Stepping rate of >40 steps per minute: purposeful steps taken
• Stepping rate of >100 steps per minute: equivalent to 2.5 mph and faster

A detailed health questionnaire was completed by each woman during at baseline. The sample was divided into 4 groups based on the average number of steps taken per day, and were then followed for an average of 4.3 years. A total of 504 women died during follow-up. After taking into account age, smoking, diet, alcohol use, body mass index, personal history of cancer and cardiovascular disease, as well as  other variables that might ‘muddy the water’, the risk of death across the 4 groups is shown below in Figure 1.

As clearly shown in the Figure, there was a significant trend for decreased risk of all-cause mortality across the four groups, with women in Group 4 having a 58% lower risk of death when compared to women in Group 1. Importantly, women in Group 2 (about 4400 steps per day), had a 41% lower risk of death than Group 1 (about 2700 steps per day).

Next, the researchers examined stepping intensity and the risk of all-cause mortality. Again, women were placed into 4 groups for each of the measures of stepping intensity listed above. For all measures of stepping intensity, risk of all-cause mortality decreased as stepping intensity increased. The researchers also found that women who took more steps per day also tended to walk at higher intensities than women who took fewer steps per day.

Finally, using women who averaged 2000 steps per day as the reference group, the researchers determine the risk of all-cause mortality using increments of 100 steps per day. They found that mortality risk steadily declined with more daily steps, up to 7500 steps per day, beyond which the risk remained the same.

There were several important conclusions made from this study:

• For older women, taking about 4400 steps per day was associated with a 41% lower risk of mortality as compared to women taking about 2700 steps per day.
• With more steps per day, mortality risk steadily decreased before leveling off at about 7500 steps per day.
• Women who take more steps per day also tend to step at higher intensities than women who take fewer steps per day
• Thus, the recommendation for 10,000 steps per day to achieve an ideal level of physical activity is likely an overestimate for older women.
• Older women who wish to take more than an average of 7500 steps per day may certainly do so, however, this will not decrease their mortality risk any further.

Reference

Lee, I-M., Shiroma, E., Kamada, M., Bassett, D., Matthews, C., Buring, J. (2019). Association of step volume and intensity with all-cause mortality in older women.  JAMA Internal Medicine. Doi:10.1001/jamainternmed.2019.0899