People who consume five servings of dark chocolate per week may have a reduced risk of developing diabetes, US researchers have reported in a new study highlighting the nuanced and long-debated relationship between chocolate and health.

The researchers who analysed chocolate consumption by over 1,92,000 study participants over an average of 25 years have found that five servings of dark chocolate were associated with a 21 per cent lower risk of type-2 diabetes — the most common form influenced by genetics, diet and lifestyle.

They also detected a dose-response relationship, meaning the more the dark chocolate, the lower the risk of diabetes. Each additional weekly serving of dark chocolate appeared to lower the risk by 3 per cent. But the study found no significant associations with milk chocolate.

“Our findings suggest that not all chocolate is created equal,” said Binkai Liu, a research scholar in the nutrition department at the Harvard T.H. Chan School of Public Health and lead author of the study published earlier this week in the British Medical Journal.

Dozens of peer-reviewed studies over the past two decades have documented that dark chocolate, particularly with high cocoa levels, offers benefits for cardiovascular health, improves blood pressure, reduces cholesterol and decreases inflammation.

But some of the findings have been inconsistent and few studies have differentiated between dark chocolate versus milk chocolate. And concerns about how excessive consumption of chocolate might contribute to weight gain, increased sugar intake and associated risks have lingered.

Liu and her colleagues tracked the records of over 1,92,000 adults who were free of diabetes at the start of a long-term health follow-up study in the US that collected information about food habits, lifestyle and health outcomes. Among nearly 1,12,000 people who specifically documented the type of chocolate they consumed — dark or milk — 4,771 developed type-2 diabetes.

They found that participants who consumed at least five portions of any type of chocolate per week had a 10 per cent lower risk of diabetes compared to those who never or rarely consumed chocolate, one portion defined as one ounce, or 28gm.

Participants who consumed five servings showed a 21 per cent lowered risk of diabetes. And increased consumption of milk chocolate — not dark chocolate — was associated with long-term weight gain, a condition that can lead to diabetes.

“We were surprised by the clear split between dark and milk chocolate’s impact on diabetes risk and long-term weight gain,” Qi Sun, an associate professor of nutrition and epidemiology who led the study, said in a media release.

Multiple earlier studies have established that dark chocolate contains compounds called flavonoids, polyphenols and stearic acid among others that benefit health through various pathways.

“Even though dark chocolate and milk chocolate may have similar levels of calories and saturated fat, it appears that the rich polyphenols in dark chocolate might offset effects of saturated fat and sugar on weight gain and diabetes,” Sun said.