A morning cup of coffee may do more than make people feel awake. A Finnish study suggests that regular coffee drinking is tied to measurable differences in body fat, muscle, blood chemistry and sex hormones.
The results may help scientists understand why coffee has repeatedly been linked with lower risks of some common metabolic diseases.
Coffee is one of the world’s most popular drinks, yet its effects on the body are surprisingly complicated.
It contains caffeine, but it also provides many other natural chemicals that may affect inflammation, blood sugar control and the way cells use energy. That makes it difficult to identify exactly which part of coffee might explain its possible health effects.
Researchers from the University of Oulu approached the question by studying a well-known group of people born in northern Finland in 1966.
Their analysis included 2,264 participants who had reached age 46. Instead of looking only at disease diagnoses, the team examined a broad set of biological measurements that can offer early clues about metabolic health.
The researchers compared how much coffee people usually drank with measurements of body fat and muscle. They also examined substances circulating in the blood and several sex hormones. This allowed them to look for a biological pattern associated with coffee rather than focusing on a single health measure.
People who reported drinking more coffee generally carried less fat. This included visceral fat, the deeper abdominal fat that surrounds organs and is often considered more harmful than fat stored directly under the skin. They also tended to have a greater amount of skeletal muscle.
Surprisingly, these differences were not obvious from BMI alone. People drinking different amounts of coffee had broadly similar BMI values. Because BMI combines weight and height without distinguishing muscle from fat, two people with the same BMI can have very different body compositions.
The blood tests added another layer to the story. Higher coffee consumption was linked with lower levels of branched-chain amino acids in both sexes. These amino acids are normal nutrients, but unusually high circulating levels have often been seen in people with insulin resistance and have been associated with future type 2 diabetes.
In men, heavier coffee drinking was also associated with a more favorable pattern involving glucose and insulin.
The researchers found higher total testosterone and higher bioavailable testosterone, along with more sex hormone-binding globulin, or SHBG. SHBG is made mainly by the liver and carries testosterone and other sex hormones in the blood.
The picture was not as simple as saying coffee raised male hormones. Measures of free testosterone and the free androgen index were modestly lower with greater coffee intake. This combination shows why hormone studies need to examine several measurements rather than relying on a single testosterone number.
Women showed fewer hormone differences. Those who drank more coffee tended to have higher SHBG and lower measures of free androgens. These sex-specific patterns interested the researchers because hormones can influence where fat is stored, how muscle is maintained and how the body responds to insulin.
Lead author Luca Verroest said the hormone signature remained even after the researchers accounted for BMI and several lifestyle factors. That does not mean hormones explain all of coffee’s possible health links, but it gives scientists another mechanism to investigate.
It may be that coffee compounds influence the liver, hormone handling or energy metabolism in ways that eventually affect disease risk.
There are good reasons not to turn these results into a prescription for extra coffee. The study did not randomly assign people to drink different amounts. It simply found that people with different coffee habits also had different biological characteristics, so cause and effect cannot be established.
For example, coffee drinkers may differ from non-coffee drinkers in exercise, food choices, sleep, smoking or many other behaviors. Statistical adjustments can reduce the influence of these factors, but they cannot remove every hidden difference.
It is also possible that a person’s metabolism or health influences how much coffee they choose to drink rather than coffee changing their metabolism.
The Finnish setting is both valuable and unusual. Finland has one of the world’s highest levels of coffee consumption, estimated at roughly 11.8 kilograms per person each year. Results from a population with such strong coffee habits may not perfectly predict what would happen in countries where coffee is prepared differently or consumed less often.
The study nevertheless has several useful features. The researchers examined more than 2,000 people of the same age and used detailed measures that went beyond weight or a simple blood sugar test. The consistent links with body composition, amino acids and hormones provide several leads that can now be tested experimentally.
The most sensible interpretation is that habitual coffee intake appears to have a recognizable metabolic and hormonal fingerprint, but scientists do not yet know whether coffee creates that fingerprint.
The results fit with earlier studies linking coffee with lower diabetes and cardiovascular risk, yet they cannot explain those associations on their own. Controlled human trials will be needed before researchers can say that changing coffee intake improves these markers.
The University of Oulu team is now investigating possible mechanisms using animal models, with hopes of eventually testing the ideas in people.
Those studies may reveal whether caffeine, other coffee compounds or a combination of ingredients is responsible. For now, the new findings deepen the scientific mystery surrounding a drink that many people consume every day.
The study, “Associations of habitual coffee intake with testosterone and cardiometabolic markers: the Northern Finland Birth Cohort 1966 study,” was published in the European Journal of Nutrition.
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Source: University of Oulu.
