Harvard Epidemiologists' Rx: Moderate-to-Vigorous Exercise

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On Nov. 6, 2017, researchers from the Harvard University School of Public Health reported in the journal Circulation that moderate-to-vigorous physical activity (MVPA) such as brisk walking is associated with up to a 70 percent lower risk of death among older women. The authors note that light-intensity physical activity was not associated with lower mortality. However, the researchers also point out that light-intensity physical activity may provide other health benefits not specifically examined during their recent clinical study.

The latest Harvard study on aerobic exercise and all-cause mortality was conducted from 2011 to 2015. This groundbreaking research is among the first to use a fitness tracking device called a “triaxial accelerometer” to investigate clinical outcomes related to frequency and intensity of physical activity.

Based on rigorous analysis of accelerometer data from 16,741 participants (average age 72), the Harvard epidemiologists concluded that MVPA was associated with roughly a 60 to 70 percent lower risk of death among the most active women, compared to mortality rates of the least active women during the four-year study.

Notably, this research indicates that previous studies, which relied on self-reporting of daily physical activity, may have inaccurately under-reported the life-extending benefits of MVPA. As first author, I-Min Lee, professor of medicine and associate epidemiologist at Harvard Medical School’s Brigham and Women's Hospital and the Harvard School of Public Health, explains:

"The fact that physical activity lowers mortality rate is nothing new – we have many studies showing this. However, previous studies have primarily relied on self-reported physical activity, and self-reports tend to be imprecise. Based on these self-report studies, we know that physical activity is associated with a 20 to 30 percent reduction in mortality rates, comparing the most with the least active. Using device-measured physical activity in the present study, we observed a 60 to 70 percent risk reduction larger than previously estimated from self-report studies.”​

Both the World Health Organization's Physical Activity Guidelines and the ODPHD Physical Activity Guidelines for Americans recommend 150 minutes per week of moderate-intensity activity or 75 minutes per week of vigorous-intensity aerobic physical activity (or a combination of the two) plus muscle-strengthening exercises at least twice a week.

Although there is a growing consensus among epidemiologists that brisk walking as a form of moderate-to-vigorous exercise is associated with increased longevity, less than 150 minutes of moderate-intensity walking per week also appears to have significant benefits.

For example, an August 2017 Tufts-led study found that inactive older adults who added just 48 minutes of moderate-intensity physical activity per week (in the form of walking-based exercises) dramatically lowered their risk of major mobility disability. Additionally, anything above 48 minutes of moderate-intensity exercise per week was a tipping point associated with improvements in overall physical functioning when compared to adults who were sedentary.

As another example, a prospective cohort study of almost 140,000 older U.S. adults, published Oct. 19, 2017, in the American Journal of Preventive Medicine, found that moderate-to-vigorous physical activity (also in the form of walking-based exercises) for less than the currently recommended guideline of 150 minutes per week was enough aerobic exercise to significantly improve public health outcomes and lower mortality risk when compared to inactivity. That said, the researchers also concluded that walking at or above physical activity recommendations of 150 minutes per week was associated with even greater decreased risk of mortality.

The most promising aspect of the latest exercise and mortality research may be that walking is statistically the most well-liked form of MVPA in the United States. Walking is commonly referred to as the “perfect exercise” by epidemiologists because it is a simple and convenient form of physical activity that is free, doesn’t require any special equipment or the hassle of changing clothes. Plus, walking can be done at any age.

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I-Min Lee of Harvard University was also involved in another international study on various types of exercise and mortality led by epidemiologists at the University of Sydney and published Oct. 31, 2017, in the American Journal of Epidemiology. This study compared mortality outcomes of strength-promoting exercise (SPE) and MVPA among a cohort of 80,306 adults.

Lee and her Australian collaborators found that regularly performing some type of muscle-strengthening exercise was associated with a 23 percent lower risk of premature death by any means and a 31 percent lower risk of cancer-related deaths. Importantly, this study also unearthed that strength-promoting exercise alone does not appear to reduce the risk of cardiovascular disease mortality, whereas moderate-to-vigorous physical activity does. Taken together, all of these findings reaffirm that a combination of SPE and MVPA is a winning formula for overall health and longevity.

For those of us who tend to avoid lifting weights, the best news from the SPE vs. MVPA study is that you don't have to become a gym rat or even pump iron to reap the benefits of strength-promoting exercises that fit your lifestyle. The researchers found that using one's own body weight to increase muscular strength by doing push-ups, sit-ups, lunges, tricep dips, etc. is just as effective as lifting weights at the gym when it comes to increasing longevity.

I-Min Lee plans to continue her ongoing epidemiologic research to pinpoint more specific dose-responses to various types, intensities and weekly amounts of exercise necessary to optimize overall well-being and longevity for people from all walks of life and ages.

In the meantime, based on the latest groundswell of empirical evidence, it seems irrefutable that both moderate-to-vigorous physical activity and strength-promoting exercise offer even greater life-extending benefits than previously recognized. Hopefully, these clinical studies will motivate you to make both MVPA and SPE a part of your weekly routine. Or to keep doing what you're doing, if these physical activities are already lifestyle habits.