This is one of those no-brainer findings that you might expect, but until scientists studied it, we could only speculate: Commuting is bad for your health. At the most basic level, it takes time away that could be spent exercising. But the new study linked commuting to actual indicators of poor health, from cardiovascular issues to obesity.

Longer commuting distances were linked to decreased cardiorespiratory fitness (CRF), increased weight, and other indicators of metabolic risk. The findings are detailed in the June issue of American Journal of Preventive Medicine.

"This study yields new information about biological outcomes and commuting distance, an understudied contributor to sedentary behavior that is prevalent among employed adults," explains lead investigator Christine M. Hoehner of Washington University in St. Louis, Missouri. "It provides important evidence about potential mediators in the relationship between time spent driving and cardiovascular mortality."

Researchers studied 4,297 residents who lived and worked in eleven counties in the Dallas-Fort Worth or Austin, Texas metropolitan areas. CRF, body mass index (BMI), and metabolic risk variables including waist circumference, fasting triglycerides, fasting plasma glucose, high-density lipoprotein (HDL) cholesterol, and blood pressure, were measured. Self-reported participation in moderate to vigorous physical activity over the previous three months was also assessed.

Those who drove longer distances to work reported less frequent participation in moderate to vigorous physical activity and decreased CRF, and had greater BMI, waist circumference, and blood pressure. The association remained when physical activity and CRF were adjusted for, although to a lesser degree for BMI and waist circumference.

Those who commuted more than 15 miles to work were less likely to meet recommendations for moderate to vigorous physical activity, and had a higher likelihood of obesity. Commuting distances greater than 10 miles were associated with high blood pressure.

Dr. Hoehner explains that longer commutes may replace participation in physical activity, given the association between commute time and physical activity and CRF, and the lesser association with adiposity after adjustment for physical activity. "At the same time, both BMI and waist circumference were associated with commuting distance even after adjustment of physical activity and CRF, suggesting that a longer commuting distance may lead to a reduction in overall energy expenditure," she notes.

Association of commuting distance with the other metabolic risk indicators was largely weak or insignificant, with the exception of blood pressure. Multiple mechanisms could be contributing to this relationship. "The Dallas-Fort Worth region is ranked among the top five most congested metropolitan areas, and those with longer commutes may be more likely to be exposed to heavy traffic resulting in higher stress levels and more time sitting," Dr. Hoehner said.