Caffeine is consumed worldwide in coffee, tea, and soft drinks, and its health benefits have been studied for years. Now, researchers have looked at the genes associated with caffeine metabolism to determine how the level of caffeine in the blood affects body fat and the risk of type 2 diabetes and cardiovascular disease.
The standard cup of coffee – in the US, that’s 8 oz or around 250 ml – contains 70 to 150 mg of caffeine. By comparison, 12 oz (around 350 ml) of caffeinated soft drink usually contains 30 to 40 mg of caffeine, and an 8-oz cup of green or black tea contains 30 to 50 mg.
Small, short-term trials have shown that caffeine intake reduces body mass index (BMI) and fat mass, but its long-term effects are unknown. Other studies have observed that drinking three to five cups of coffee daily reduces the risk of type 2 diabetes and cardiovascular disease. But most studies have not been able to reliably establish a causal link between caffeine intake and disease.
Caffeine is metabolized largely by the liver, but its metabolization can be affected by variations of the genes CYP1A2 and AHR. People with variations of these genes metabolize caffeine more slowly, so while they consume less coffee on average, their blood caffeine levels are higher.
A new study has examined these genetic variations using a mendelian randomization framework to investigate whether long-term exposure to higher blood caffeine levels has a causal effect on BMI, type 2 diabetes, and cardiovascular disease.
. By using the mendelian randomization method – a technique that uses genetic variants reliably related to a modifiable risk factor (here, blood caffeine levels) to obtain evidence about the causal influence of that risk factor – the researchers could differentiate between the effects of caffeine and the effects of other substances present in caffeinated drinks.
The researchers analyzed data obtained from genome-wide association studies (GWAS) of 9,876 individuals of European ancestry, examining the role of CYP1A2 and AHR genetic variants.
Analysis showed that genetically predicted higher blood caffeine levels were associated with lower BMI and body fat and with a lower risk of type 2 diabetes. Moreover, almost half – 43% – of the effect on diabetes risk was driven by a reduction in BMI. There was no evidence of a significant association between genetically predicted higher blood caffeine levels and cardiovascular disease, particularly ischemic heart disease, atrial fibrillation, heart failure, and stroke.
The researchers point to their use of the mendelian randomization technique as a strength of the study because, by using fixed genetic variants, bias is reduced.
“Our mendelian randomization finding suggests that caffeine might, at least in part, explain the inverse association between coffee consumption and risk of type 2 diabetes,” said the researchers.
They are aware of the study’s limitations, one being that participants were only of European descent, so the results might not be generalizable to non-European populations. However, the researchers consider that the study’s results warrant the consideration of including caffeinated drinks as a preventative measure.
“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,” researchers said.
The study was published in the journal BMJ Medicine.
Source: Karolinska Institutet via Scimex
