Chocolate is one of the most confusing foods in nutrition science – hailed as a superfood for its potential heart, brain, and anti-inflammatory benefits, yet criticized as sugary, fatty junk food that’s easy to overeat.

Nutrition research is notoriously tricky, said dietitian Julie Stefanski, MEd, a spokesperson for the Academy of Nutrition and Dietetics, and chocolate studies can be particularly challenging. Differences in people’s lifestyles, diets, and personal factors – like genetics or medical conditions – mean results “might not be able to be applied to all people,” she said. In studies, “dark chocolate” could mean cocoa powder, supplements, or candy bars – crucial differences that make it hard to compare results.

Scientists do agree on one thing. If chocolate has health benefits, they likely come from flavonols— plant compounds thought to support heart health, improve blood vessel function, and reduce inflammation. This insight has shifted chocolate research toward exploring how flavonols might slow “inflammaging” – the low-grade, chronic inflammation that naturally rises with age and increases health risks, including risks to your heart and blood vessels.

“The ‘how’ part is really the critical question,” said Howard Sesso, ScD, an epidemiologist at Harvard Medical School and author of two new studies exploring just that. Now Sesso and other scientists are getting closer to that “how” – and that clearer picture could help people make sense of how to enjoy chocolate in a healthier way.

In Sesso’s latest study people who took a daily cocoa flavonol supplement for two years had significantly lower levels of c-reactive protein (CRP) – a marker of inflammation linked to heart disease – compared with those on a placebo. That may help explain why people in the landmark COSMOS trial (COcoa Supplement and Multivitamin Outcomes Study) who took the same supplement had a 27% lower risk of dying from heart disease. “What we see here is not just [how] cocoa flavonols specifically, but how flavonols – even in other foods – might improve inflammation,” Sesso said.

Flavonols’ effect on heart and blood vessel function may be the key – improved blood flow helps the body keep inflammation in check and maintain healthier blood vessels as we age. If cocoa flavonols help lower or slow the rise of CRP levels over time – or, as scientists say, improve the CRP “trajectory” – that could explain how cocoa reduces risks to the heart and blood vessels. The idea that flavonols act on the vascular system aligns with other research, such as Sesso’s other recent study, published in August, linking them to resistance against age-related blood pressure increases.