Blood Caffeine Levels May Affect Body Fat and Type 2 Diabetes Risk

Blood caffeine levels may influence how much body fat a person has, which could subsequently shape their likelihood of developing type 2 diabetes and cardiovascular diseases.

This was the conclusion of a 2023 study that used genetic markers to identify a clearer connection between caffeine concentrations, BMI and the risk of type 2 diabetes.

Researchers at the Karolinska Institute in Sweden, the University of Bristol in the UK and Imperial College London in the UK suggested that calorie-free drinks containing caffeine could be investigated as a possible way to help lower body fat.

Caffeine levels, BMI and type 2 diabetes risk

"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 an overview of the research:

The analysis drew on data from just under 10,000 people held in existing genetic databases. It concentrated on variants within, or close to, particular genes associated with the rate at which the body breaks down caffeine.

Generally, people with variants that affect the CYP1A2 gene and the AHR gene, which regulates it, process caffeine more slowly, meaning it stays in their bloodstream for longer. However, they also typically consume less caffeine overall.

The researchers applied a method known as Mendelian randomization to assess probable causal links between these variants, conditions such as diabetes, body mass and lifestyle factors.

Although caffeine levels showed a significant association with BMI and the likelihood of type 2 diabetes, blood caffeine concentrations were not linked with cardiovascular diseases, including atrial fibrillation, heart failure and stroke.

What caffeine may do to body fat

Earlier research has associated moderate, relatively higher caffeine intake with improved heart health and a lower BMI. This study provides further detail about the effects of coffee on the body.

It is also important to remember that caffeine does not affect the body only positively. Its possible benefits must therefore be weighed carefully when considering consumption, although this research marks a significant step towards determining the ideal amount of caffeine.

"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 believes the association identified may result from caffeine's ability to raise thermogenesis, or heat production, and fat oxidation, the process of converting fat into energy. Both processes have an important role in overall metabolism.

Further research on caffeine-containing drinks

Despite the study's large sample, Mendelian randomization has limitations, and unaccounted-for factors may still be involved. Further studies will be required to establish 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 research appeared in BMJ Medicine.

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