Higher blood caffeine levels may help people stay slim and cut their risk of diabetes, genetic evidence suggests.
A new study found that the rate at which we metabolise caffeine may have an impact on our weight, though further research will be needed to work out whether drinking more coffee is beneficial.
Dr Dipender Gill, a clinical scientist at Imperial College London, worked on the new research published in the journal BMJ Medicine.
He said existing studies had not been able to show a causal effect between caffeine and weight, but the new study looked at genetics, making the findings more robust.
He told the PA news agency that “95% of your caffeine is metabolised by an enzyme” and that two genes called CYP1A2 and AHR affect the function and level of that enzyme.
He said: “So, using these genetic variants that cause people to metabolise caffeine faster or slower, we found that slower metabolisers have higher plasma (blood) caffeine levels, and those with higher plasma caffeine levels go on to have a lower body mass index and a lower risk of diabetes.
“It’s the plasma caffeine that’s doing that.”
He said that, on a population level, this means that people who metabolise caffeine more slowly are more likely to be thinner and have less risk of diabetes.
He added: “If you’re a faster metaboliser, you have lower plasma caffeine levels and you are, on average at a population level, at slightly higher risk of diabetes and have a slightly higher body mass index.”
He said the present study will direct further research, including on whether drinking more coffee can help people stay slim.
However, people should not change their habits for now.
He said: “Certainly people shouldn’t start drinking more coffee or tea to try and lose weight, and that’s also because coffee and tea and caffeine can have adverse effects as well.
“So some people might find it difficult to sleep and some people can get palpitations, so I think, based on this study, people should not change their lifestyle or behaviour, but our findings should be used to direct further research including potential clinical studies.”
Dr Gill said it is currently unclear what proportion of the population metabolises caffeine more quickly.
The study included almost 10,000 people who were taking part in six longer-term studies.