- Modern lifestyles mean that people spend an increasing amount of time sitting, whether working at a desk, watching TV, or travelling by car, train or plane.
- Prolonged sitting can adversely affect the function of the blood vessels.
- A new study has found that foods high in flavanols — antioxidants found in plant foods, such as cocoa, tea, and some fruits and vegetables — may improve vascular function during sitting or being sedentary.
Sitting for long periods is linked to declines in vascular function, particularly in the legs, even in people who are physically fit. Recent research suggests that adults in the United States sit for at least 6 hours every day, and adolescents even more.
However, many of us have sedentary jobs, spend a lot of time travelling by car, train, or plane, or enjoy watching TV or playing computer games, so we may spend much of the day sitting down.
Now, researchers from the University of Birmingham, in the United Kingdom, have found that flavanols may help counteract the effects of prolonged sitting.
In their small-scale study, published in
“Even though the trial was small, its randomized, double-blind, placebo-controlled, crossover design gives it strong internal validity for detecting acute physiological changes. However, the external validity is narrow: all were young, healthy, male, and the experiment lasted only two hours. The outcome, flow-mediated dilation, is a well-validated marker of endothelial function but still a surrogate, not a clinical endpoint. Thus, the findings are mechanistically meaningful but not clinically definitive.”
—Christopher Yi, MD, board certified vascular surgeon at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the study.
Researchers recruited 40 healthy men, ages between 18 and 34, into the study. Half were high in fitness, and half were low, as measured by a cardiorespiratory fitness test conducted by the researchers.
Before the experimental visits, participants fasted for 12 hours, and avoided caffeine, alcohol, polyphenol-containing foods and drinks, and any vigorous exercise for 24 hours.
Upon arrival, they rested in a supine position for 15 minutes, after which researchers measured their blood pressure, resting heart rate, flow-mediated dilatation (FMD, a higher value indicating better vascular function) in the superior femoral and brachial arteries, and tissue oxygenation in the gastrocnemius (calf) muscle.
As soon as these tests were completed, participants sat still in a comfortable chair for 2 hours, with their legs parallel and both feet flat on the floor. They were allowed to make gentle arm movements, such as using a computer, writing, or texting.
When they sat down, researchers gave them a randomly assigned high-flavanol cocoa or low-flavanol cocoa drink to consume within 10 minutes. The drinks, made using cocoa and 350ml spring water, were identical apart from their flavanol content, 695mg in the high-flavanol drink, and 5.6mg in the low-flavanol.
During sitting, researchers recorded tissue oxygenation in the medial gastrocnemius, and after 2 hours, they repeated the other 4 tests done at the start.
Researchers assessed FMD of the superior femoral and brachial arteries using ultrasound.
They found no differences in
In both arteries, FMD reduced during sitting in the low-flavanol group, and not in the high-flavanol group. After sitting, FMD remained higher in the high-flavanol than the low-flavanol group. Neither measure was influenced by the individual’s fitness.
“We have known for some time that flavanols have benefical effects for blood flow from observational studies. It is surprising we can see such strong effects from one off dose on negative effects of sitting down.”
— Eamon Laird, Assistant Lecturer in Human Nutrition at Atlantic Technological University Sligo and Adjunct Assistant Professor Trinity College Dublin, who was also not involved in the study.
Yi was particularly interested in one of the findings:
“Previous research already showed that prolonged sitting impairs endothelial function, and that cocoa flavanols acutely enhance FMD in other contexts. The novel contribution here is showing that flavanols can preserve both upper- and lower-limb endothelial responsiveness during sitting and that cardiorespiratory fitness did not confer natural protection.”
Laird told Medical News Today:
“Essentially, [flavanols] increase nitric oxide (NO) production that helps blood vessels relax and dilate, improving circulation. They can also reduce inflammation and have been associated with reduced oxidative stress. We are also unsure if the other dietary components that are often found with flavanols may also have an additive beneficial effect.”
“Flavanols enhance endothelial nitric-oxide (NO) signaling by stimulating endothelial NO synthase (eNOS) activation, reducing oxidative stress and superoxide-mediated NO breakdown, and improving vascular smooth-muscle responsiveness to NO.”
“By preserving NO bioavailability, flavanols maintain vasodilatory capacity and counteract the temporary endothelial ‘stiffening’ that occurs when leg blood flow and shear stress fall during sitting,” he added.
Experts agreed that although flavanols had a positive effect on vascular function, exercising or keeping active throughout the day is likely the most effective approach.
“Flavanol consumption may buffer the short-term vascular stress caused by sitting, but movement remains the most powerful tool for vascular health. […] The most effective strategy is to take regular breaks from sitting by standing up or walking for a few minutes every 30 minutes, which helps restore blood flow and shear stress in your arteries. Even small movements, such as calf raises, fidgeting, or using a foot pedal under your desk, can keep circulation active and reduce the negative effects of prolonged immobility.”
— Christopher Yi
“In addition to movement, maintaining a consistent aerobic exercise routine strengthens overall endothelial health, while a diet rich in fruits, vegetables, tea, berries, and other polyphenol-containing foods provides further antioxidant and anti-inflammatory support. Managing blood pressure, cholesterol, and blood sugar remains essential for long-term vascular protection. Flavanol-rich foods and drinks should be viewed as helpful adjuncts — not replacements — for an active lifestyle.”
Laird echoed this warning:
“These findings […] are highly significant and could be an easy, enjoyable way to try and stave off effects of sitting down. However, it is not a magic bullet and we shouldn’t take this study as evidence to eat chocolates everyday as they contain fat, sugar, and energy!”