7 miles, 14,000 steps: Keeping your heart healthy according to a study of postal workers

We may need to walk seven miles a day and spend seven hours on our feet to avoid heart disease, a study with postal workers suggests.

Of the 111 participants in the study, those who had desk jobs, not walking delivery routes, had a bigger waist circumference—97 cm compared to 94 cm—and approximately one BMI unit difference. They also had a higher risk of cardiovascular disease—2.2 percent compared to 1.6 percent over ten years.

The new study suggests that waist circumference increases by two centimeters, and risk of cardiovascular diseases by 0.2 percent, for every additional hour of sitting beyond five hours. Furthermore, LDL cholesterol increases and HDL cholesterol decreases with each of those additional hours.

“Longer time spent in sedentary posture is significantly associated with larger waist circumference, higher triglycerides (fat in the blood), and lower HDL cholesterol, all adding up to worse risk of heart disease,” says study leader William Tigbe of the University of Warwick’s Warwick Medical School.

“The levels associated with zero risk factors were walking more than 15,000 steps per day, which is equivalent to walking seven to eight miles, or spending seven hours per day upright.

“Our findings could be used as the basis of new public health targets for sitting, lying, standing, and stepping to avoid metabolic risks. However the levels suggested in our research would be very challenging to achieve unless incorporated into people’s occupations.”

The study participants wore a tiny physical activity and position monitor called activPAL, invented by coauthors from Glasgow Caledonian University, strapped to their thigh for seven days, except during activities that risked it being in contact with water, e.g. bathing or swimming. They also had their weight, height, and blood pressure measured, and provided blood samples. Cardiovascular risks were assessed using the PROCAM risk calculator, which takes into account age, sex, family history, blood pressure, and metabolic measures.

The study took place between September 2006 and September 2007 and volunteers were recruited from the Royal Mail in Glasgow. Only apparently healthy, non-smokers, with no personal history of heart attack, stroke, coronary heart disease, hypertension, or diabetes were included. None of the participants was on any lipid, blood pressure, or glucose lowering medication.

“Our evolution, to become the human species, did not equip us well to spending all day sitting down. We probably adapted to be healthiest spending seven to eight hours every day on our feet, as hunters or gatherers,” says Mike Lean of the University of Glasgow’s School of Medicine.

“Our new research supports that idea. The ‘bottom’ line is that if you want to be sure of having no risks of heart disease, you must keep off your bottom!”

The study, part of Tigbe’s PhD project, appears in the International Journal of Obesity.