“Desk-bound workers at double DVT risk,” reads the headline in The Daily Telegraph today. Workers who “sit at a desk for eight hours a day and spend more than three hours without stretching double their risk of developing deep vein thrombosis (DVT)”, the newspaper says.
The newspaper story is based on a study which looked at people admitted to hospital for blood clots or heart problems and compared how long they had sat at a desk for each day in total and how long the longest period was that they stayed seated for. However, the results should be interpreted cautiously because of the study’s limitations; the estimate of a two-fold increase in risk was not statistically significant and therefore cannot be seen as a reliable estimate. The risk of developing a blood clot for most office workers will be very low, however, it seems sensible to suggest that remaining immobile for long periods in any setting should be avoided.
Dr Jill West and colleagues from the Capital & Coast District Health Board, Medical Research Institute of New Zealand, the University of Otago Wellington and the University of Southampton in the UK carried out this research. The study reported no sources of funding. It was published in the_ Journal of the Royal Society of Medicine_ , a peer-reviewed medical journal.
This was a case control study. The researchers enrolled 97 adults (cases) aged under 65 who consecutively attended an outpatient venous thromboembolism (VTE) clinic between October 2005 and December 2006. These people had been discharged from hospital in the previous 12 months after treatment for deep vein thrombosis (DVT, 53 people), pulmonary embolism (PE, 29 people) or both (15 people). The diagnoses were confirmed by standard methods. The researchers also enrolled 106 similarly aged adults admitted to the coronary care unit (controls).
Cases and controls were interviewed and asked questions about their VTE or heart problem and about risk factors for VTE, including age, family history of VTE, medical risk factors (such as pregnancy), surgery or trauma, prolonged travel, prolonged seated immobility at work in the four weeks before they suffered from VTE and the total prolonged seated immobility (work, travel to and from work, and at home seated at the computer) in the four weeks before they suffered from VTE. Prolonged seated immobility was defined as:
The researchers then compared periods of immobility for cases and controls. They adjusted for the other risk factors for VTE in their analyses (not including surgery/trauma, as only one person had this risk factor).
The average age of the case group was 44.9 years and the control group was 52.4 years. Most (about two thirds) of the controls had been admitted to hospital for heart disease. Although the odds of developing VTE was increased about two-fold in people who had prolonged periods of immobility at work or in total, this increase was no longer statistically significant when the analysis was adjusted for other risk factors for VTE.
The researchers found that an increase of an extra hour in the maximum total time seated at work increased odds of VTE by 10%, and an extra hour in the maximum total time seated at work without getting up increased odd by 20%. Both of these increases only just reached statistical significance, both before and after adjustment for other risk factors.
The researchers concluded that their study provided “preliminary evidence that prolonged seated immobility at work may represent a risk factor for VTE requiring hospital admission”.
This study has a number of limitations, and there are some points that it is important to keep in mind when interpreting this study:
The risk of developing a VTE for most office workers will be very low. Although the estimate of increased risk from this study may not be reliable, prolonged periods of immobility, for example during travel, have been linked to an increase risk of blood clots in other studies, and it seems sensible to avoid long periods of immobility in any setting if possible. The researchers call for larger studies and for evaluation of chair design to further an understanding of the mechanisms involved.
Every hour get active; I am planning for computers to go down every hour for two minutes only to be reactivated by action.