When researchers compared sitting time with the incidence of specific illnesses, two separate studies resulted in both predictable and surprising conclusions. In one study, the researchers linked the number of hours spent sitting to symptoms of depression; yet, in another study they found no relationship between sitting time and the occurrence of cardiovascular disease.

Depression

Seemingly as common as bouts with the flu, depression affects more than 350 million people of all ages from around the globe, according to the World Health Organization. Although, at its worst, depression may lead to suicide, more commonly it leads to disability such that an affected individual would function poorly at work, at school, and in the family. More women than men are affected by depression. The Mayo Clinic finds that women are nearly twice as likely as men to develop depression. About one in five women develop it at some point in her life, and although depression can occur at any age, it is overall most common in women between the ages of 40 and 59.

To discover more about depression, particularly its association with sitting time and physical activity, researchers from Victoria University and University of Queensland in Australia examined data from 8,950 women who were aged 50 to 55 years of age in 2001. Study participants completed mail surveys in 2001, 2004, 2007, and 2010. Researchers then assessed the information received from each woman. Depression or lack of symptoms was compared with each woman’s reported sitting time and physical activity. Sitting time fell into three categories — four hours or less per day, four to seven hours per day, or greater than seven hours per day — while physical activity was counted as none, some, or meeting standard guidelines.

As one might suspect, the women who sat for more than seven hours each day and the women who did no physical activity were more likely to have depressive symptoms than women who sat four or less hours each day and who met physical activity guidelines. When the researchers modeled sitting time and physical activity together, the likelihood of depressive symptoms in women who sat more than seven hours per day and did no physical activity was triple that of women who sat four or less hours each day and met physical activity guidelines. Also unsurprisingly, the researchers found that women who did no physical activity were more likely than those who met physical activity guidelines to have future depressive symptoms.

“Increasing physical activity to a level commensurate with guidelines can alleviate current depression symptoms and prevent future symptoms in mid-aged women,” wrote the researchers in their paper. “Reducing sitting-time may ameliorate current symptoms.”

Cardiovascular Disease

The World Health Organization finds that, by 2030, more than 23 million people will die annually from cardiovascular diseases. In the U.S., the most common type of heart disease is coronary artery disease, which may lead to a heart attack in some individuals. Commonly, scientists cite unhealthy diet, physical inactivity, tobacco use, and harmful use of alcohol as behavioral risk factors.

“In Westernized societies many adults spend much of their day engaged in sedentary activities that involve low energy expenditure,” wrote the authors of a study published in the International Journal of Behavioral Nutrition and Physical Activity. “Although there is growing evidence on the relationship between television/screen time and increased cardiovascular disease mortality, very little is known about the association between total sitting time (in different domains) and cardiovascular disease incidence.”

Researchers from University of Queensland decided to investigate a possible relationship, then, between sitting and cardiovascular disease among middle-aged women in Australia. They examined data from 6,154 participants in the Australian Longitudinal Study on Women's Health. Born between the years 1946 and 1951, the chosen women were all free of cardiovascular disease at the beginning of the study. The researchers employed survival analysis to determine any links between self-reported sitting time and cardiovascular disease incidence, determined through hospital diagnoses and cause of death data.

Contrary to their expectations, the researchers found 177 cases of cardiovascular disease among the women studied, but sitting time was not associated with these incidents. Extending the comparison further, the researchers discovered no interaction among physical activity and sitting time and cardiovascular disease.

“In mid-aged women sitting time does not appear to be associated with cardiovascular disease incidence,” wrote the authors. "Research in this area is scarce and additional studies are needed to confirm or refute these findings.”

Sources: Herber-Gast GM, Jackson CA, Mishra GD, Brown WJ. Self-reported sitting time is not associated with incidence of cardiovascular disease in a population-based cohort of mid-aged women. International Journal of Behavioral Nutrition and Physical Activity. 2013.

Van Uffelen JGZ, van Gellecum YR, Burton NW, Peeters G, Heesch KC, Brown WJ. Sitting-Time, Physical Activity, and Depressive Symptoms in Mid-Aged Women. American Journal of Preventive Medicine. 2013.