Caffeine linked to lower BMI and reduced risk of type 2 diabetes

Genetic evidence indicates that higher levels of caffeine in a person’s blood may be linked with lower weight.

But people shouldn’t assume that drinking more coffee will be a route to weight loss, says Dipender Gill at Imperial College London, who helped carry out the study.

Caffeine is the most widely used psychoactive substance, with many people consuming several beverages of coffee or caffeinated soft drinks a day.

Numerous studies have previously suggested that caffeine consumption is linked with lower weight. But these were mainly observational studies, which recorded people’s health and their caffeine consumption, making it hard to know if caffeine caused the effects or just correlated with them.

Gill’s team used an alternative approach, looking at genetic differences in how quickly people break down caffeine to mimic the effects of giving different doses in a randomised trial.

There are two genes that affect people’s ability to break down caffeine, meaning that after consuming the same amount of it, people with different variants would have different levels of it in their blood.

Gill and his colleagues analysed data from several previous studies that sequenced people’s DNA and tracked their health. They included nearly 10,000 people in total, although most included only people of European ancestry.

The studies didn’t analyse blood samples, but previous work has shown that those who break down caffeine more slowly have higher levels of it in their blood on average – even though they tend to drink less coffee.

The team found that people genetically predisposed to have higher caffeine levels had a lower body mass index (BMI), a measure of a person’s weight in relation to their height; lower fat mass; and a lower likelihood of having type 2 diabetes, a condition linked with being overweight.

“We know that caffeine affects metabolism and how energetic someone is. It makes sense that there might be an association,” says Benjamin Woolf at the University of Bristol, UK, who wasn’t involved in the study.

Gill says people shouldn’t change their drinking habits based on these results – and that people wanting to lose weight should be especially wary of consuming milky and sugary coffee drinks. “A lot of caffeinated beverages are quite calorific,” he says. “Caffeine can have other detrimental effects, including effects on sleep and heart function.”

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