Two 46-year-olds can share a BMI and still carry very different bodies. A new analysis of the Northern Finland Birth Cohort 1966 found that people who drank more coffee carried less total and visceral fat, and more skeletal muscle, than lighter drinkers with a similar BMI. The pattern held in both sexes. In men, heavier coffee intake also tracked with a more favorable glucose-insulin profile and higher total and bioavailable testosterone. Because the study is observational, it can’t show that coffee caused any of these differences.

Coffee ranks among the most consumed beverages worldwide, and Finland drinks more of it than almost anywhere else, at roughly 11.8 kilograms per person a year. Earlier research has tied coffee to lower rates of type 2 diabetes and cardiovascular disease, but the biology behind that link has stayed murky. Findings on coffee and testosterone have stayed limited and inconsistent, and that gap is what this study set out to address. Luca Verroest of the University of Oulu led the work.

Researchers drew on the Northern Finland Birth Cohort 1966, a population-based cohort followed since birth. At the 2012 follow-up, when members turned 46, researchers invited 10,331 people and 5,832 attended a clinical examination. This analysis used data from 2,264 of them who had complete information on habitual coffee intake, body composition, blood metabolites, and sex hormones. Participants self-reported their coffee intake. Because the design is cross-sectional, every result below reflects a correlation measured at a single point in time, not a before-and-after comparison.

Higher coffee intake matched lower total and visceral fat and greater skeletal muscle mass, even among people with similar BMI scores. Both sexes also showed lower circulating branched-chain amino acids with higher coffee intake; elevated levels of these amino acids have previously been linked to insulin resistance and diabetes risk.

The hormonal picture split along sex lines. Men who drank more coffee had a more favorable glucose-insulin profile, higher total and bioavailable testosterone, and higher sex hormone-binding globulin (SHBG). Free testosterone and the free androgen index came out modestly lower in the same men. In women, the hormonal signal was narrower: higher coffee intake mainly tracked with higher SHBG and lower measures of free androgens.

These directions describe associations with higher habitual coffee intake, not specific measured amounts; the source material didn’t report effect sizes.

Verroest and colleagues frame the hormone findings as a possible piece of the coffee-metabolism puzzle rather than an answer. «What stood out in our findings was a distinct hormonal signature that didn’t disappear even after we took into account BMI and lifestyle factors,» Verroest said. The team suggests hormonal pathways may partly explain coffee’s previously observed links to metabolic health, while stressing that association isn’t proof. They describe animal studies now underway, with human intervention trials as the eventual goal before any dietary advice follows.

Several caveats limit how far these findings reach. Because the study is cross-sectional, it can only show a correlation, not proof that coffee causes any of this. Participants reported their own coffee habits rather than having them measured, and almost nobody in the cohort abstained entirely, so the comparison to true non-drinkers rests on a small group. Finland’s population is also fairly homogeneous, which limits how far the results travel to other countries. Coffee contains more than 1,000 compounds, and this study didn’t test which one, if any, drives the pattern. Animal studies come next, the authors say, with human trials the eventual goal before any dietary advice follows.