A large Korean study shows that drinking black coffee, especially among women, is linked to better glucose control and reduced insulin resistance, highlighting coffee’s potential role in metabolic health.

Study: Association Between Coffee Consumption and Glucose Metabolism Markers in Korean Adults. Image Credit: Shutterstock AI Generator / Shutterstock.com

A recent study published in Nutrients explores the association between coffee consumption and glucose metabolism in Korean adults.

Can coffee help regulate blood sugar and support diabetes care?

Coffee is one of the most popular beverages worldwide; however, existing studies have reported mixed results on its health impact.

Although each additional cup of coffee has been suggested to reduce the risk of type 2 diabetes mellitus (T2DM) by 6%, irrespective of the presence of caffeine, the mechanisms involved in this association remain unclear. Previous in vitro and in vivo studies have reported that coffee’s abundant polyphenols can improve insulin sensitivity, which is crucial for diabetes management to reduce insulin resistance (IR).

In 2019, Koreans drank 315 grams of total beverages per capita, 108 grams of which were coffee. Various types of coffee are consumed in South Korea, with instant coffee mix, which is high in sugar and saturated fatty acids, constituting a significant portion of the Korean coffee market.

To date, few studies have considered coffee type while assessing the association between coffee intake and glucose metabolism.

About the study

Data were obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) between 2019 and 2021. A total of 7,453 adults between 19 and 64 years of age were asked about their coffee intake and the type of coffee they consumed over a 24-hour period.

The type of coffee reported was either black coffee or coffee with sugar and/or cream. Study participants were categorized as non-drinkers and those who drank one, two, and three or more cups/day.

In large-scale epidemiological studies, IR is typically measured using the homeostasis model assessment of insulin resistance (HOMA-IR). High HOMA values have historically been correlated to an increased risk of metabolic diseases like hypertension and T2DM.

For the current analysis, researchers investigated the impact of coffee consumption on various glucose metabolism markers, including hemoglobin A1c (HbA1c), HOMA-IR, HOMA-β, fasting glucose, and fasting insulin levels.

Study findings

Overall, consuming two cups of coffee daily was associated with a 23% reduced risk of elevated fasting insulin or HOMA-IR. For black coffee, HOMA-IR and fasting insulin levels were reduced by 26% and 21%, respectively, among those who consumed one cup or less of black coffee every day.

No significant reduction in HOMA-IR or fasting insulin levels was observed among individuals who consumed two or more cups of coffee daily. Adding sugar and/or cream to coffee did not affect this association.

Women who drank two or more cups of coffee exhibited more pronounced improvements in HOMA-IR and fasting insulin levels by 27% and 30%, respectively. These benefits were further amplified in women who consumed three or more cups daily, with a 34% and 36% reduction in HOMA-IR and fasting insulin levels, respectively. No significant difference in HOMA-IR or fasting insulin levels was observed when the addition of sugar and/or cream was considered.

However, women who drank black coffee exhibited better insulin resistance and glucose metabolism than those who included sugar and/or cream in their coffee. Two cups of black coffee every day were associated with a 36% reduction in both HOMA-IR and fasting insulin levels.

These benefits were no longer significant when three or more cups of black coffee were consumed every day. This lack of significance may be due to a smaller number of individuals drinking three or more cups of coffee daily.

The observed sex differences could be due to different sex-hormone-binding globulin (SHBG) levels, which are low in many patients with T2DM but higher in women due to the presence of estrogen. Women are also less likely to smoke or drink, which may amplify the role of diet in maintaining glucose metabolism.

No significant difference in HbA1c or HOMA-β was associated with coffee consumption, corroborating previous studies’ results.

Coffee reduces glucose metabolism markers by improving insulin sensitivity rather than enhancing beta cell function. Previously, researchers have hypothesized that several different mechanisms may be involved in coffee’s anti-diabetes effects, some of which are attributed to the anti-inflammatory and antioxidant properties of caffeine and other coffee compounds, reduced glucose absorption, and reduced glucose release from the liver.

Conclusions

Consuming two or more cups of black coffee per day is inversely associated with insulin resistance in Korean women.”

The current study is the first to use nationally representative KNHANES data to examine the associations of coffee drinking with glucose metabolism by type of coffee consumed. Future studies are needed to validate these findings.