Sitting for long periods can harm your blood vessels and increase heart disease risk, even in young, healthy people. Scientists tested whether a special compound found in cocoa called flavanols could protect blood vessels during 2 hours of sitting. Forty young men either drank cocoa with high flavanols or low flavanols before sitting. The results showed that the high-flavanol cocoa prevented the normal damage to blood vessels that sitting causes, and this worked equally well for both fit and less-fit people. This suggests that eating flavanol-rich foods during long sitting periods might be a simple way to protect your heart health.

The Quick Take

  • What they studied: Can a special compound in cocoa protect your blood vessels from damage caused by sitting for 2 hours straight?
  • Who participated: 40 young, healthy men between ages 18-35. Half were very fit (trained athletes), and half were less fit. All were healthy with no heart problems.
  • Key finding: Men who drank cocoa with high flavanols before sitting showed no damage to their blood vessels, while men who drank low-flavanol cocoa had the normal blood vessel damage that sitting causes. This protection worked equally well for both fit and less-fit men.
  • What it means for you: If you sit for long periods at work or school, eating flavanol-rich foods like dark chocolate or cocoa before or during sitting may help protect your heart health. However, this is just one study in young, healthy men, so more research is needed before making major dietary changes.

The Research Details

This was a carefully controlled experiment where 40 young men each participated twice. On one day, they drank cocoa with high flavanols (a special plant compound), and on another day, they drank cocoa with very low flavanols. Neither the participants nor the researchers knew which drink had the high flavanols until after the study ended. Before and after 2 hours of sitting, scientists measured how well their blood vessels worked using ultrasound technology that shows how blood vessels expand when blood flow increases.

The researchers split the men into two groups: 20 who were very fit (trained regularly) and 20 who were less fit. This allowed them to see if fitness level made a difference in how flavanols protected blood vessels. They measured blood vessel function in the leg (femoral artery) and arm (brachial artery), as well as blood pressure and blood flow patterns.

This study design is important because it controls for many factors that could affect results. By having each person do both the high-flavanol and low-flavanol trials, researchers could compare the same person under different conditions. The double-blind design (where neither participants nor researchers knew which drink was which) prevents bias from affecting the results. Testing both fit and less-fit people shows whether fitness protects against sitting damage or if flavanols help everyone equally.

This study has several strengths: it used a rigorous design with proper controls, tested both arms and legs, and included both fit and less-fit individuals. The main limitation is that it only tested young, healthy men, so results may not apply to women, older adults, or people with existing health conditions. The study was also short-term (just one 2-hour sitting session), so we don’t know if benefits continue with regular use or if they work during typical daily sitting patterns.

What the Results Show

The main finding was clear: sitting for 2 hours damaged blood vessel function in both the leg and arm arteries in all participants. This damage appeared as reduced ability of blood vessels to expand when blood flow increased. However, men who consumed the high-flavanol cocoa before sitting showed no blood vessel damage—their vessels worked just as well after sitting as before.

Interestingly, fitness level didn’t matter. Both the very fit men and the less-fit men experienced the same blood vessel damage from sitting, and both groups were equally protected by the high-flavanol cocoa. This is important because it suggests that even if you exercise regularly, you still need to protect your blood vessels during sitting time.

The flavanols did not affect blood pressure or overall blood flow patterns—they specifically protected the ability of blood vessels to expand and contract properly. This suggests flavanols work through a specific mechanism related to the inner lining of blood vessels (called the endothelium), which is responsible for healthy vessel function.

The study also measured oxygen levels in leg muscles during and after sitting. Sitting caused oxygen levels to drop within 10 minutes, and this effect continued throughout the 2-hour period. Interestingly, the high-flavanol cocoa did not prevent these oxygen changes, suggesting flavanols protect blood vessel function through a different mechanism than improving oxygen delivery to muscles. Blood pressure increased slightly during sitting in both groups, but flavanols did not prevent this increase.

Previous research has shown that sitting damages blood vessels and increases heart disease risk. This study builds on that knowledge by testing whether nutrition can prevent this damage. Earlier studies suggested flavanols from cocoa and other plant foods have heart-protective effects, but this is one of the first studies to specifically test whether they can prevent sitting-related blood vessel damage. The findings support the idea that what you eat during sedentary time matters for heart health.

This study only included young, healthy men (average age around 25), so results may not apply to women, older adults, or people with existing heart conditions or diabetes. The study tested only one 2-hour sitting session, so we don’t know if benefits continue with repeated use or during typical daily sitting patterns with breaks. The flavanol dose used (150 mg) is higher than what most people would get from eating regular chocolate, so it’s unclear how much cocoa or dark chocolate you’d need to eat for real-world benefits. Finally, the study didn’t measure long-term health outcomes, only immediate blood vessel function changes.

The Bottom Line

Based on this research, consuming flavanol-rich foods before or during long sitting periods may help protect your blood vessels. Good sources include dark chocolate (70% cocoa or higher), unsweetened cocoa powder, and tea. However, this recommendation has moderate confidence because the study was small, short-term, and only tested young, healthy men. It should be combined with other proven strategies like taking movement breaks every 30 minutes, stretching, and regular exercise.

This research is most relevant to young, healthy adults who sit for long periods at work or school. Office workers, students, and people with desk jobs should find this particularly useful. However, people with heart disease, high blood pressure, or diabetes should talk to their doctor before making dietary changes based on this study. The findings may not apply to older adults, women, or people with existing health conditions, as they weren’t tested in this study.

The blood vessel protection from flavanols appeared immediately—within the 2-hour sitting period tested. However, we don’t know how long the protection lasts after you stop consuming flavanols, or whether regular consumption provides ongoing benefits. You would likely need to consume flavanol-rich foods before or during each sitting session to get protection during that sitting period.

Want to Apply This Research?

  • Log your sitting time in 30-minute blocks and track when you consume flavanol-rich foods (dark chocolate, cocoa, tea). Measure your sitting sessions and note whether you consumed flavanols before sitting. Over time, you can track patterns of sitting duration and flavanol consumption to build better habits.
  • Set a reminder to consume a small amount of dark chocolate or cocoa drink 15-30 minutes before you know you’ll be sitting for extended periods. For example, have a cup of hot cocoa before a long study session or work meeting. Start with small amounts (about 1 ounce of dark chocolate or 1 cup of cocoa) and track how this fits into your daily routine.
  • Track your daily sitting time and flavanol consumption for 2-4 weeks to establish a baseline. Then intentionally consume flavanol-rich foods before your longest sitting periods and note any changes in how you feel (energy levels, alertness, leg heaviness). While you can’t measure blood vessel function at home, you can track subjective feelings and sitting patterns to see if the strategy becomes a sustainable habit.

This research describes findings from a single study in young, healthy men and should not be considered medical advice. The study tested a specific high dose of flavanols that is higher than typical food amounts. If you have heart disease, high blood pressure, diabetes, or other health conditions, consult your doctor before making dietary changes based on this research. This study does not replace established recommendations for heart health, including regular exercise, not smoking, and maintaining a healthy diet. While the findings are promising, more research in diverse populations is needed before making strong health claims.