Your Coffee Habit May Do More Than Wake You Up — Especially For Men

There's a rhythm to the first cup of the day. The grinder, the kettle, a few minutes of silence before anyone needs anything from you. Almost nobody files that under health decisions, because it's just how the morning works.

In Finland, though, researchers have been following the same group of people since they were born in 1966, and at age 46 they compared their coffee habits1 against body composition, blood sugar, and hormones.

Coffee isn't just caffeine. It contains more than 1,000 active compounds, including antioxidant chlorogenic acids, and regular coffee drinking has been linked to lower rates of type 2 diabetes and heart disease.

But its relationship with hormones is less clear, even though testosterone and sex hormone-binding globulin (SHBG), a protein that binds testosterone in the blood, can influence body fat and insulin sensitivity.

Finland is an especially useful place to investigate this because it has the world's highest coffee consumption per person. Researchers analyzed data from 2,264 adults in the Northern Finland Birth Cohort 1966, all of whom were 46 years old and all but 70 of whom drank coffee.

Participants reported how many cups they typically drank each day, then had fasting blood tests and body measurements taken. The researchers also accounted for factors including BMI, education, smoking, exercise, and alcohol use.

People who drank more coffee tended to have less body fat, less visceral fat (the fat stored around the organs), and more muscle, even though their BMI was about the same.

But there's an important caveat: The researchers didn't break these body-composition results down by sex, and men were more common among the heaviest coffee drinkers, so the difference may not be entirely about coffee.

The hormone findings were more interesting. In men, each extra cup of coffee was linked to higher total testosterone, bioavailable testosterone (the testosterone available for tissues to use), and SHBG, a protein that binds testosterone in the blood.

Because SHBG was higher, free testosterone, or testosterone not bound to SHBG, was actually lower. Women also had higher SHBG and lower free testosterone with higher coffee intake, but no change in total or bioavailable testosterone.

Higher coffee intake was also linked to lower fasting insulin and better insulin sensitivity in men.

In both men and women, heavier coffee drinking was associated with lower levels of branched-chain amino acids, which are often higher when insulin resistance is developing.