Sitting for long hours found to reduce blood flow to the brain

A team of researchers with Liverpool John Moores University in the U.K. has found evidence of reduced blood flow to the brain in people who sit for long periods of time. In their paper published in the Journal of Applied Physiology, the group outlines the experiments they carried out with volunteers and what they found.

26 aug 2018--Most people know that sitting for very long periods of time without getting up now and then is unhealthy. In addition to contributing to weight gain, sitting for a long time can cause back pain and leg problems and possibly other ailments. And now, evidence has been reported that it can reduce blood flow to the brain—something shown in the past to contribute to the likelihood of developing neurological disorders such as dementia.
Suspecting that sitting for a long time could cause circulation problems to the brain, the researchers enlisted the assistance of 15 adult volunteers—each of them had a day job that required long hours of sitting. Each of the volunteers participated in three exercises over a period of time—each came to the lab on three separate occasions and sat for four hours. On each visit, they were fitted with a headband that measured blood flow to the brain using ultrasound. Each subject also wore a face mask that captured and measured carbon dioxide levels.
During the first exercise, the volunteers were asked to sit at a desk for four straight hours, leaving their chairs only to use the restroom. For the second exercise, each rose from their chair every 30 minutes and walked on a treadmill for two minutes. In the third exercise, each subject remained in their chair for two hours and then walked on the treadmill for eight minutes, then returned to the chair.
The researchers found evidence of reduced blood flow in all of the volunteers during all of the exercises. However, they also found that normal blood flow was restored by walking breaks. They report that the best outcome was when the volunteers took frequent two-minute walking breaks.

More information: Sophie E. Carter et al. Regular walking breaks prevent the decline in cerebral blood flow associated with prolonged sitting, Journal of Applied Physiology (2018). DOI: 10.1152/japplphysiol.00310.2018

Abstract

Decreased cerebrovascular blood flow and function are associated with lower cognitive functioning and increased risk of neurodegenerative diseases. Prolonged sitting impairs peripheral blood flow and function, but its effects on the cerebrovasculature are unknown. This study explored the effect of uninterrupted sitting and breaking up sitting time on cerebrovascular blood flow and function of healthy desk workers. Fifteen participants (10 male, 35.8±10.2 years, BMI: 25.5±3.2 kg∙m^-2) completed, on separate days, three 4-hr conditions in a randomised order: a) uninterrupted sitting (SIT), b) sitting with 2-min light intensity walking breaks every 30-min (2WALK) or c) sitting with 8-min light intensity walking breaks every 2-hrs (8WALK). At baseline and 4-hrs, middle cerebral artery blood flow velocity (MCAv), carbon dioxide reactivity (CVR) of the MCA and carotid artery were measured using transcranial Doppler (TCD) and duplex ultrasound respectively. Cerebral autoregulation (CA) was assessed with TCD using a squat-stand protocol and analysed to generate values of gain and phase in the very low, low, and high frequencies. There was a significant decline in SIT MCAv (-3.2±1.2 cm.s^-1) compared to 2WALK (0.6±1.5 cm.s^-1, p=0.02), but not between SIT and 8WALK (-1.2±1.0 cm.s^-1, p=0.14). For CA, the change in 2WALK very low frequency phase (4.47±4.07 degrees) was significantly greater than SIT (-3.38±2.82 degrees, p=0.02). There was no significant change in MCA or carotid artery CVR (p>0.05). Results indicate that prolonged, uninterrupted sitting in healthy desk workers reduces cerebral blood flow, however this is offset when frequent, short-duration walking breaks are incorporated.

Poorer Kidney Function Associated With Cerebral Small Vessel Disease

Caroline Cassels
January 21, 2008 — New research suggests that poor kidney function, which is known to increase cardiovascular risk, might also be associated with subclinical markers of cerebral small vessel disease, independent of cardiovascular risk factors.
In a large population-based study, investigators from Erasmus Medical Center, the Netherlands, found that individuals with a lower glomerular filtration rate (GFR) had less deep white-matter volume (WMV), more white-matter lesions (WML), and a more frequent presence of lacunar infarcts, although this did not reach statistical significance.
Furthermore, adjustment for cardiovascular risk factors, such as blood pressure, C-reactive protein (CRP), and homocysteine, only marginally changed the association between GFR and cerebral small vessel disease, a common cause of stroke, cognitive decline, and dementia.
The study, led by M. Arfan Ikram, MD, was published in the January issue of Stroke.
The investigators speculate that, based on the study's findings, it is possible that GFR provides a better marker than concomitantly measured cardiovascular risk factors.
However, they add, more research to elucidate the exact mechanisms underlying the association of GFR with cerebral small vessel disease is required to confirm this hypothesis.
"Given that cerebral small vessel disease is related to an increased risk of stroke, cognitive decline, and dementia, our data provide important information in addition to the known risk of adverse cardiac outcomes in persons with poor kidney function. Thus, our study further emphasizes the importance of identifying those with subclinical kidney disease," they write.
Marginal Change After Risk-Factor Adjustment
Designed to examine age-related brain abnormalities on magnetic resonance imaging (MRI), the cross-sectional study, known as the Rotterdam Scan Study (RSS), is a substudy of the Rotterdam Study, a large population-based investigation of the prevalence, incidence, and determinants of chronic disease in the elderly.
The investigation looked at 484 subjects between the ages of 60 and 90 years who were free of dementia at the study outset and who underwent MRI scans and had their GFR measured using the Cockcroft-Gault equation.
Global, lobar, and deep volumes of gray and white matter and volume of WML were measured using automated MRI analysis. Lacunar infarcts were rated visually.
Blood glucose level, blood pressure, cholesterol, CRP, and homocysteine were measured in each participant. Subjects were also screened for a history of myocardial infarction and smoking.
The investigators found that subjects in the lowest quartile of kidney function had smaller brain volumes. However, they noted that this smaller brain volume was not attributable to smaller gray-matter volume but rather to smaller total and normal WMV.
They found no association between GFR and either lobar or deep gray-matter volume.
The authors report that, after adjustment for cardiovascular risk factors, the associations were marginally attenuated, but GFR was still related to volume of WML, to deep WMV, and to brain volume.
Collaboration Needed
In an accompanying editorial, Stephen L. Seliger, MD, MS, from the University of Maryland in Baltimore, and W.T. Longstreth Jr, MD, MPH, from the University of Washington in Seattle, note that the study adds to a growing body of evidence supporting a link between vascular disease of the kidney and the brain.
However, they add, at this point the underlying mechanisms are unclear.
"Understanding the interplay of vascular disease in these 2 organs holds the promise of finding novel means to reduce the risk of impaired function, especially in the brain. The path to this understanding begins with the type of study reported by Ikram and colleagues and requires the continued collaboration of nephrologists and neurologists," they write.
The study was supported by the Health Research and Development Council and the Netherlands Organization for Scientific Research.
Stroke. 2008; 39:55-61 Abstract, 5-6. Abstract