Regular coffee consumption has already been linked to improved heart health and a lower risk of developing type 2 diabetes. However, the relationship between coffee and those health conditions is still unclear. New research from Finland seems to show a link between daily coffee consumption and differences in overall body fat, metabolism and sex hormones, with stark variations between men and women.
How the Study Was Organized
Published in the European Journal of Nutrition, the study analyzed information from 2,264 people aged 46, all of whom had participated in the Finland Birth Cohort 1966. Researchers from the University of Oulu divided participants into four groups based on their coffee habits, ranging from no coffee to five or more cups a day. Only 70 participants claimed they never drank coffee.
The researchers examined blood sugar and insulin, metabolic markers, body composition and sex hormones. Simultaneously, they looked at 164 blood-based lipid and metabolic measures.
Differences in Body Composition
Those in the study who drank more coffee had less total body fat and less visceral fat around internal organs, while also displaying greater skeletal muscle mass. However, body mass index (BMI) was similar across the four participant groups.
So, the study suggested that while heavier coffee drinkers don’t necessarily weigh less, they do display different body composition, with more muscle and reduced fat.
Glucose Responses
Participants were given a glucose drink to test how their bodies dealt with sugar over two hours. The results suggested that men who drank more coffee had lower fasting insulin and lower insulin levels during the test.
Additionally, some measures suggested greater insulin sensitivity and lower insulin resistance. On the other hand, women showed substantially fewer links between coffee and insulin control, although the study couldn’t identify a reason.
The study also found that higher coffee intake was related to lower levels of branched-chain amino acids (BCAAs) in men and women. These biomarkers have been associated with insulin resistance and increased risk of type 2 diabetes. Still, the study couldn’t prove that higher coffee consumption is directly related to disease prevention or lowered BCAA levels.
Hormone Changes
In men, researchers discovered that, in general, testosterone levels increased with coffee consumption. In fact, the study showed higher total testosterone, bioavailable testosterone and sex hormone-binding globulin (SHBG) in men who drank moderate to high amounts of coffee each day.
However, the study doesn’t show that drinking more coffee increases testosterone in men. This is because researchers also found that free testosterone and the free androgen index were modestly lower.
As for the women in the study, researchers didn’t find the same association with total or bioavailable testosterone. Rather, hormonal associations mainly pointed to lower measures of free androgens and higher SHBG.
Study Limitations
Seeing as this study was purely observational, it can’t establish cause-and-effect relationships. Rather, it can suggest relationships between coffee consumption and metabolic health. What’s more, researchers relied on participants’ reporting of how much coffee they drank, and cup sizes weren’t standardized.
Moving forward, the study’s authors hope to establish whether or not coffee does indeed cause the differences observed. And if so, a controlled study will be necessary to identify which compounds may be responsible. As Luca Verroest, lead author of the study and Doctoral Researcher at the University of Oulu puts it, “Coffee is consumed by millions of people every day, yet we still know surprisingly little about how it relates to our metabolism and hormones.”