Blood caffeine levels may affect body fat and type 2 diabetes risk

Caffeine has a wide range of effects on the human body, including some you might not anticipate.

Evidence suggests one example is that the concentration of caffeine in your bloodstream may be linked to how much body fat you carry.

That, in turn, could influence your likelihood of developing type 2 diabetes and cardiovascular diseases.

What the 2023 study found about caffeine, BMI and type 2 diabetes

These points come from a 2023 study that used genetic markers to draw a clearer connection between plasma caffeine levels, BMI, and the risk of type 2 diabetes.

The researchers-based at the Karolinska Institute in Sweden, the University of Bristol in the UK, and Imperial College London in the UK-suggested that calorie-free caffeinated drinks could be investigated as one possible route to lowering body fat.

"Genetically predicted higher plasma caffeine concentrations were associated with lower BMI and whole body fat mass," the researchers wrote in their paper, published in March 2023.

"Furthermore, genetically predicted higher plasma caffeine concentrations were associated with a lower risk of type 2 diabetes. Approximately half of the effect of caffeine on type 2 diabetes liability was estimated to be mediated through BMI reduction."

Watch the video below for a summary of the research:

How the researchers studied blood caffeine levels

The analysis drew on data from just under 10,000 people, taken from existing genetic databases. The focus was on differences in, or close to, particular genes known to affect how quickly caffeine is metabolised.

Broadly, people with certain variants-especially in CYP1A2 and in a gene that controls it, called AHR-tend to break down caffeine more slowly. This means caffeine stays in the bloodstream for longer, even though these individuals also tend to consume less caffeine overall.

To examine probable cause-and-effect links between these genetic variants, conditions such as diabetes, body mass, and lifestyle factors, the team used a method known as Mendelian randomisation.

Links to cardiovascular diseases were not found

Although the study identified a meaningful association between plasma caffeine levels, BMI, and type 2 diabetes risk, it did not find a link between blood caffeine concentration and cardiovascular diseases. This included atrial fibrillation, heart failure, and stroke.

Earlier research has connected moderate-and comparatively higher-caffeine intake with improved heart health and lower BMI. This new work adds finer-grained detail to what is already understood about how coffee affects the body.

At the same time, caffeine’s effects are not universally beneficial. That means the potential upsides need to be balanced carefully against the downsides-yet this study represents a useful step towards clarifying what an ideal caffeine level might look like.

"Small, short-term trials have shown that caffeine intake results in weight and fat mass reduction, but the long term effects of caffeine intake is unknown," the researchers explained.

"Considering the extensive intake of caffeine worldwide, even its small metabolic effects could have important health implications."

The team suggests the relationships observed may be partly explained by caffeine’s tendency to increase thermogenesis (heat production) and fat oxidation (converting fat into energy), both of which are central to overall metabolism.

Limitations and what comes next

Although the dataset was large, Mendelian randomisation is not perfect. It remains possible that other, unmeasured factors contributed to the observed patterns. Further studies will be required to confirm cause and effect.

"Randomized controlled trials are warranted to assess whether non-caloric caffeine-containing beverages might play a role in reducing the risk of obesity and type 2 diabetes," said University of Bristol genetic epidemiologist Benjamin Woolf.

The study was published in BMJ Medicine.

An earlier version of this article was published in March 2023.