People who regularly consume more coffee may have a lower proportion of total and visceral fat and, at the same time, greater muscle mass, according to the results of a new Finnish study. In men, higher coffee consumption was also found to be associated with characteristics of testosterone levels and more favorable indicators of glucose and insulin metabolism.
The study was published in the scientific journal European Journal of Nutrition. The researchers used data from the large-scale Northern Finland Birth Cohort 1966 project, whose participants have been followed since birth. The analysis included 2,264 people aged 46.
The participants were divided according to their habitual coffee consumption. Seventy people practically did not consume coffee, 296 drank one to two cups a day, 822 drank three to four cups, and another 1,076 participants drank five or more cups daily.
The researchers found an interesting pattern: body mass index did not differ significantly between the groups, but body composition did.
Participants who consumed more coffee had, on average, a lower percentage of body fat, lower total fat mass and a smaller area of visceral fat. At the same time, they had greater skeletal muscle mass. Differences in body composition were observed in both men and women.
“This study is interesting primarily because it demonstrates the limitations of the familiar BMI indicator. Two people may have practically the same body mass index but a completely different ratio of fat to muscle tissue. In the Finnish sample, it was body composition, rather than BMI, that was associated with the level of coffee consumption,” notes Sviatoslav Morozov-Leonov, Doctor of Biological Sciences and head of a division at the Experts Club analytical center.
The researchers separately studied hormonal indicators. In men, each additional cup of coffee per day was statistically associated with an increase in total testosterone of approximately 0.29 nmol/L and in bioavailable testosterone of approximately 0.08 nmol/L. The level of sex hormone-binding globulin — SHBG — also increased. These associations persisted after statistical adjustment for BMI, education, smoking, physical activity and alcohol consumption.
However, the hormonal results turned out to be considerably more complex than the phrase “coffee increases testosterone” might suggest.
Along with higher total and bioavailable testosterone, greater coffee consumption in men was associated with lower free testosterone and a lower free androgen index. In women, the researchers found no statistically significant association between the amount of coffee consumed and total or bioavailable testosterone. At the same time, women also had higher SHBG and lower free androgen indicators.
“Therefore, it would be incorrect to conclude from the study that five cups of coffee a day increase testosterone in men. The hormonal picture is much more complex: total testosterone increased, but free testosterone decreased at the same time. The authors themselves speak of a specific hormonal profile rather than a proven stimulating effect of coffee,” Morozov-Leonov emphasized.
Another interesting result is related to metabolism.
In men with higher coffee consumption, the researchers identified a more favorable profile of glucose and insulin indicators. In representatives of both sexes, coffee consumption was also inversely correlated with blood concentrations of branched-chain amino acids — BCAAs.
Elevated BCAA concentrations have been associated in a number of previous studies with insulin resistance and an increased risk of metabolic disorders. The authors of the Finnish study believe that the detected changes may help to better understand the association between coffee consumption and metabolic health observed in other studies.
At the same time, the scientists specifically warn that the results do not prove a cause-and-effect relationship.
The study was cross-sectional: coffee consumption, body composition, hormones and metabolic indicators were assessed essentially during the same period of time. Therefore, it is impossible to determine whether coffee led to the observed differences or whether people with a particular lifestyle and metabolic profile simply consumed coffee more often.
In addition, the participants self-reported the amount of coffee they consumed, while the group of people who did not consume coffee at all was small — only 70 people out of 2,264. The Finnish population is also relatively homogeneous, so the results cannot automatically be extrapolated to the populations of other countries.
“This is a good example of how nutrition studies should be read. An association between a product and a particular health indicator does not yet mean that the product is the cause of that effect. Practical recommendations require prospective studies and, most importantly, randomized controlled trials,” says Experts Club representative Morozov-Leonov.
The authors also do not recommend increasing coffee consumption on the basis of the results obtained. They point to the need for further research, including intervention studies in humans, which would make it possible to establish whether a causal relationship exists and which specific biologically active components of coffee may be responsible for the observed associations.
Coffee contains more than a thousand different compounds, so the potential mechanism of action remains uncertain. The researchers consider hormonal and metabolic changes to be one of the possible directions for further study of coffee’s effects on health.
“The most interesting result of the work is not the assertion that ‘the more coffee, the better.’ The study shows a much more complex relationship between habitual diet, body composition, hormones and metabolism. Testing these mechanisms in long-term and controlled studies should be the next stage,” Sviatoslav Morozov-Leonov summarized.
The study Associations of habitual coffee intake with testosterone and cardiometabolic markers: the Northern Finland Birth Cohort 1966 study. The analysis included 2,264 participants from the Northern Finland Birth Cohort 1966. The authors declared no conflict of interest.
