“These findings offer important insight"
Drinking coffee may help people reduce body weight and cut their risk of diabetes.
Researchers used a statistical technique called Mendelian randomisation, which uses genetic variants as a tool to investigate the causal relationship between a trait and an outcome.
The results of their analysis showed that higher genetically predicted blood caffeine levels were associated with lower body weight (BMI).
Higher genetically predicted blood caffeine levels were also associated with a lower risk of Type 2 diabetes.
The findings suggest that it may be worth exploring the potential for calorie-free caffeinated drinks to play a role in lowering the risk of obesity and Type 2 diabetes.
The study was a collaboration between researchers from Imperial College London, the University of Bristol, the London School of Hygiene and Tropical Medicine, and Uppsala University in Sweden.
Dr Dipender Gill, senior author for the study, from Imperial College London’s School of Public Health, said: “These findings offer important insight into the potential causal effect of caffeine on adiposity [obesity] and diabetes risk.
“However, further clinical study is warranted before individuals should use these results to guide their dietary preferences.”
Previous research indicated that drinking around three cups of coffee a day is associated with a lower risk of Type 2 diabetes and cardiovascular disease.
An average cup of coffee contains around 70–150 mg of caffeine.
But researchers stated that most of the current published research has come from observational studies, which cannot reliably establish causal effects, because of the other potentially influential factors involved.
It is also difficult to disentangle any specific effects of caffeine from other compounds included in caffeinated drinks and foods.
Using Mendelian randomisation, the researchers looked at the role of two common genetic variants of the CYP1A2 and AHR genes in nearly 10,000 people of predominantly European ancestry, who were taking part in six long-term studies.
The CYP1A2 and AHR genes are associated with the speed of caffeine metabolism in the body.
Dr Gill that people who metabolise caffeine more slowly are more likely to be slimmer and have less risk of diabetes.
He said: “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.”
The researchers also studied the extent to which any effect of caffeine on Type 2 diabetes risk might be driven by concurrent weight loss.
The results showed that weight loss drove 43% of the effect of caffeine on Type 2 diabetes risk.
No strong associations emerged between genetically predicted blood caffeine levels and the risk of any of the studied cardiovascular disease outcomes.
The researchers acknowledge that there are limitations to the study, including the use of only two genetic variants, and the inclusion of only people of European ancestry.
Further research will be carried out, including on whether drinking more coffee can reduce the risk of diabetes.
Despite this, Dr Gill says people should not change their habits for now.
“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.”