People who drank more coffee tended to have less body fat, more muscle and differences in several markers related to metabolism and sex hormones, according to a study of more than 2,200 middle-aged adults in Finland.
The findings, published in the European Journal of Nutrition, suggest habitual coffee drinking may be connected with several aspects of metabolic and hormonal health. But the study measured coffee intake and health markers at the same point in time, so researchers cannot determine whether coffee produced those differences or whether other characteristics of coffee drinkers help explain them.
Researchers analyzed data from 2,264 men and women taking part in the Northern Finland Birth Cohort 1966, a long-running study that has followed people born in northern Finland in 1966. All participants in the new analysis were 46 years old.
Higher coffee intake was associated with differences in body composition even among people with similar body mass index, or BMI.
People who drank more coffee tended to have less total body fat and less visceral fat, the fat stored around internal organs. They also tended to have more skeletal muscle.
That distinction is notable because BMI measures weight relative to height but does not show how much of that weight comes from fat or muscle.
Researchers also found that people who drank more coffee had lower levels of branched-chain amino acids circulating in their blood. These amino acids come from protein and play normal roles in the body, but persistently higher blood levels have been associated in previous research with insulin resistance and type 2 diabetes.
In men, higher coffee intake was also associated with a more favorable pattern of glucose and insulin markers.
The hormone results were more complicated.
Men who drank more coffee tended to have higher levels of total testosterone and bioavailable testosterone. At the same time, measures of freely circulating testosterone were slightly lower.
One possible piece of that puzzle is sex hormone-binding globulin, or SHBG, a protein that carries sex hormones through the bloodstream. Coffee intake was associated with higher SHBG levels in both men and women. Because SHBG affects how much testosterone is freely available to tissues, different measures of testosterone can move in different directions at the same time.
That means the findings should not be interpreted as evidence that drinking more coffee simply “boosts testosterone.”
Among women, coffee intake showed fewer associations with sex hormones. Higher consumption was mainly associated with higher SHBG and lower measures of freely available androgens, a group of hormones that includes testosterone.
“Coffee is consumed by millions of people every day, yet we still know surprisingly little about how it relates to our metabolism and hormones,” said lead author Luca Verroest, a doctoral researcher at the University of Oulu. “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, with several of these associations differing between men and women.”
Researchers accounted for several factors that could affect the results, including BMI and lifestyle characteristics. Even so, observational studies cannot eliminate all of the differences between people who drink more or less coffee.
The study also provides only a snapshot at age 46. It cannot establish which came first.
For example, coffee itself could influence some of the biological markers researchers measured. But people with different body composition, metabolic health or lifestyle habits might also consume different amounts of coffee. Other characteristics not fully captured in the analysis could contribute to the associations as well.
The Finnish setting is another consideration. Coffee consumption is particularly common in Finland, and drinking habits, serving sizes and preparation methods may not be identical to those in the United States or other countries.
The study also does not show that drinking more coffee prevents type 2 diabetes or cardiovascular disease, improves body composition or produces beneficial changes in sex hormones.
Instead, the researchers say the findings may help identify biological pathways worth studying more closely. Future experiments will be needed to determine whether coffee or particular compounds in it actually produce these changes.
The research was supported by the European Union's Horizon Europe research program through the Marie Skłodowska-Curie Doctoral Network NUTRIOME. The Northern Finland Birth Cohort has also received support from the University of Oulu, Oulu University Hospital, Finnish Foundation for Cardiovascular Research, Finland's Ministry of Health and Social Affairs, National Institute for Health and Social Welfare, Regional Institute of Occupational Health and European Regional Development Fund.