Coffee drinking is linked to a lower risk of kidney damage in people with type 2 diabetes, a new study reports.
Interestingly, coffee drinking seems more beneficial for people with poorer glucose control than those with better glucose control.
The study, “Relationship of coffee consumption with a decline in kidney function among patients with type 2 diabetes: The Fukuoka Diabetes Registry,” was published in Journal of Diabetes Investigation.
Chronic kidney disease, defined as an estimated glomerular filtration rate (eGFR) less than 60 mL/min/1.73m2, is a serious complication of diabetes that increases medical costs and reduces the quality of life. While drugs play a role in diabetes management, lifestyle improvements, particularly healthier diets, frequent exercise and quitting smoking, are crucial for blood sugar control and preventing complications such as kidney disease.
Coffee was once considered potentially harmful to health; however, new studies show that it contains several antioxidant compounds that protect against heart disease and diabetes. Frequent coffee drinking is also linked to a lower risk of death from all causes in people with diabetes.
However, whether coffee protects people with type 2 diabetes from kidney disease is unknown. Now, a team of scientists in Japan investigated if a link exists between coffee drinking and kidney function in people with type 2 diabetes.
Participants for the study were recruited from the Fukuoka Diabetes Registry – a multicentre prospective study of adult patients who attend teaching hospitals or clinics certified by the Japan Diabetes Society in Fukuoka.
All eligible participants provided lifestyle information, including alcohol intake, smoking habits, frequency of exercise and medical data, including glycated haemoglobin (HbA1c) levels, albuminuria (quantity of albumin in the urine) and kidney function measured as eGFR. Participants also completed a dietary questionnaire, providing details of their coffee, calorie, and protein intake. Coffee intake was divided into four categories: no coffee, less than one cup daily, one cup daily, and at least two cups daily.
A total of 3,805 individuals, 55.5% male with a mean age of 64 years, participated in the study. During the follow-up period, 840 participants developed chronic kidney disease. Participants who drank the least coffee were more likely to develop kidney disease than those drinking more coffee.
Although kidney function declined more rapidly in participants who drank less coffee, people drinking more than two cups of coffee daily did not have a lower risk of kidney disease than those consuming less than one cup. Notably, people who drank any amount of coffee had a significantly lower risk of kidney disease than those who drank none.
“In the present study, the relative reduction in risk of a decline in eGFR was almost the same among participants that were consuming less than one, one or two cups per day, whereas a previous study showed a dose-dependent effect of coffee consumption to reduce the incidence of CKD [chronic kidney disease],” the scientists wrote.
Interestingly, participants with poorer glucose control (HbA1c greater than 8%) and high coffee intake had a lower risk of kidney damage than those with better glucose control (HbA1c less than 8%) and high coffee intake.
“Coffee consumption was significantly associated with a lower risk of decline in eGFR in patients with type 2 diabetes, and the finding remained statistically significant after adjustment for the level of glycaemic control. Furthermore, participants with poor glycaemic control (baseline HbA1c ≥8%) gained more benefit from coffee consumption than those with better glycaemic control (baseline HbA1c ≤8%),” they wrote.
The researchers do not understand how drinking coffee lowers the risk of kidney disease but speculate it may be linked to the antioxidant compounds they contain, such as caffeine chlorogenic acid.
“The biological mechanisms underlying the lower risk of impaired kidney function related in coffee consumers are not fully understood, partly because coffee is a complex mixture of substances. There is speculation regarding the specific components of coffee that affect kidney function.
Some bioactive chemicals, such as caffeine and phenolic components, have been proposed to have favourable effects. Chlorogenic acid is a phenolic component that has been shown to affect health through various mechanisms, including through effects on antioxidant capacity and chronic inflammation,” the scientists wrote.
The researchers highlighted some limitations of the study, including its observational design and measuring coffee intake with a single self-reported questionnaire.
Although the study shows a link between drinking coffee and a lower risk of kidney disease, coffee alone cannot be considered as a therapy for diabetes. It must be used in conjunction with a healthy, nutritious diet.
“Coffee is one of the most frequently consumed beverages worldwide and cannot be considered separately from the nutritional therapy for diabetes,” they wrote
Still, “we have shown that coffee consumption is significantly associated with a lower risk of a decline in eGFR, implying progressive impairment in renal [kidney] function, in patients with type 2 diabetes… these findings may be important for their clinical care,” they concluded.
The researchers state that a randomised clinical trial is necessary to confirm the protective effect of coffee intake on kidney function.
Coffee contains many antioxidant compounds, such as chlorogenic acid and caffeine, that lower the risk of many conditions, including heart disease and diabetes. This study has found a link between high coffee intake and a lower risk of chronic kidney disease in people with type 2 diabetes. And high coffee intake seems to be more beneficial for people with poor glucose control.
However, it is crucial to note that this study is observational, and it is impossible to say whether coffee directly influences kidney health in type 2 diabetes. The researchers considered confounding factors such as age, medication use, diet, smoking, exercise, and albuminuria but still found a link between coffee drinking and kidney disease. Despite this, randomised controlled trials are still necessary to clarify if coffee drinking reduces the risk of kidney disease in type 2 diabetes.
That said, coffee drinking as a part of a healthy, balanced diet may be beneficial.