What Do Double-Decker Buses Tell Us About Our Health?

We've all seen images of double-decker buses, and some of us have even rode on them. But what do double-decker buses tell us about our health?

About 70 years ago Jeremy Morris and his colleagues examined the activity levels among different occupations. They found that the sedentary drivers of London's double-decker buses had higher rates of cardiovascular disease than the conductors who climbed the stairs and walked around the bus taking people's tickets during their workday.

The data were so compelling because the bus drivers and conductors were similar demographically. That is, the bus drivers and conductors were the same age and social class. There was only one obvious difference between these two groups: The drivers were sedentary, and the conductors were unavoidably active. In fact, the conductors ascended and descended 500 to 750 steps per working day. And they were half as likely as the drivers to die from a sudden heart attack.

Morris and his colleagues also found that postmen who delivered the mail by either bike or on foot had fewer heart attacks than the sedentary men who either served behind the counters or as the telephone switchboard operators. Although collectively these early studies provided evidence for a role of physical activity in averting premature mortality, it has only recently been advanced that some of these observed associations may be explained by differences in time spent sitting rather than the time spent being physically active. That is, the bus drivers sat more than the conductors, and the telephone switchboard operators and clerks sat more than the postmen.

Within the last few decades, researchers have made a concerted effort to examine the health effects of sitting. For example, Emma Wilmot and her colleagues reviewed data from almost 800,000 participants that examined the association of sedentary time with diabetes, cardiovascular disease and all-cause mortality. They found that higher levels of sedentary behavior were associated with a 112 percent increase in the risk of diabetes, 147 percent increase in the risk of cardiovascular disease, 90 percent increase in the risk of cardiovascular mortality, and a 47 percent increase in the risk of all-cause mortality.

These associations were largely independent of physical activity, revealing that sedentary behavior and moderate-to-vigorous physical activity are distinct behaviors. This means that even if people are meeting the physical activity guidelines – yet spend most of the remaining waking hours left in sedentary activities – this has a negative impact on their health.

The bottom line (no pun intended) is that prolonged sitting time is associated with increased disease and death, independent of exercise. In other words, we need to not only move more but we also need to stand up more during the day. Let's not make "sitting the new smoking" of our generation.

Heather Hausenblas, PhD