Abstract
Irisin, secreted by skeletal muscle and possibly fat, is hypothesized to play an important role in modulating energy expenditure, obesity and metabolism. Coffee consumption also increases energy expenditure and leads to positive metabolic effects, but whether these effects are mediated by irisin remains unknown. The objective of this study was to determine the association between baseline irisin levels and the metabolic profile in humans and to investigate whether consumption of caffeinated coffee alters irisin levels. To this end, a secondary analysis was performed investigating irisin levels at baseline and after eight weeks in 32 healthy, overweight coffee drinkers who were randomized to consumption of 5 cups per day of instant caffeinated coffee, decaffeinated coffee, or water. Spearman correlation and analysis of covariance analyses were performed to identify possible associations. Irisin levels were positively correlated with waist circumference (r = 0.41, p = 0.02), fat mass (r = 0.44, p = 0.01) and CRP (r = 0.47, p = 0.007). Though there was a trend towards increased levels of irisin over time in the caffeinated coffee group (+1.8%) when compared to the placebo group (−4%) this did not reach statistical significance (p = 0.75 for the trend). This first randomized trial failed to reveal any effects of coffee consumption on irisin levels, but a larger trial, appropriately sized on the basis of data provided by this study, is needed to conclusively investigate such a relationship.Trial RegistrationClinicaltrials.gov NCT00305097
Highlights
Irisin is a novel myokine thought to play an important role in energy expenditure by mediating the exercise-induced browning of fat [1,2,3]
Three crosssectional studies in humans have demonstrated that irisin levels are lower in patients with type II diabetes, suggesting irisin could play a protective role in glucose homeostasis [4,6,7]
The association between irisin and body mass index (BMI) is more controversial with two studies showing a negative relationship [4,6] and three others showing a positive association [7,8,9]. While some of this discrepancy could be attributed to the different and better validated assay used in the latter three studies, it is possible that irisin regulation is more complex than first suspected [10]. Having reported the latter relationship between BMI and irisin in our prior study [8], we proposed that irisin could be secreted in an effort to counteract insulin resistance in the obese but that once metabolic disease occurs, irisin resistance develops, similar to several known hormone resistance syndromes [11]
Summary
Irisin is a novel myokine thought to play an important role in energy expenditure by mediating the exercise-induced browning of fat [1,2,3]. The association between irisin and body mass index (BMI) is more controversial with two studies showing a negative relationship [4,6] and three others showing a positive association [7,8,9] While some of this discrepancy could be attributed to the different and better validated assay used in the latter three studies, it is possible that irisin regulation is more complex than first suspected [10]. Having reported the latter relationship between BMI and irisin in our prior study [8], we proposed that irisin could be secreted in an effort to counteract insulin resistance in the obese but that once metabolic disease occurs, irisin resistance develops, similar to several known hormone resistance syndromes [11]. Associations between irisin and metabolic factors need to be further clarified, via simple association studies and using models that adjust for potential confounders such as obesity
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