By studying telomere length, a biological marker of ageing, researchers observed that people who drank three to four cups of coffee a day had the longest telomeres, indicating slower biological ageing. Remarkably, these individuals appeared to be biologically about five years younger than non-coffee drinkers. However, the benefits disappeared beyond this intake, reinforcing that moderation remains key.

Globally, nearly one in every seven people, about 1.1 billion individuals, were living with a mental disorder in 2021, with anxiety and depressive disorders being the most common. In India, official estimates suggest that nearly 15 per cent of the adult population experiences mental health issues requiring medical or psychological intervention. Considering that mental health disorders represent a major global public health challenge, these findings take on added significance.

What the study revealed

Drinking a maximum of three to four cups of coffee a day may slow the biological ageing of people with severe mental illness by lengthening their telomeres, indicators of cellular ageing, and giving them the equivalent of five extra biological years compared with non-coffee drinkers, finds research published in the open-access journal BMJ Mental Health. However, no such effects were observed beyond this quota, which is the maximum daily intake recommended by several international health authorities, including the NHS and the US Food and Drug Administration.

Telomeres sit on the ends of chromosomes and perform a protective role similar to the plastic tips on the ends of shoelaces. Each time a cell divides, telomeres naturally shorten. Over time, excessive shortening contributes to ageing and disease. While telomere shortening is a natural biological process, it appears to be accelerated in people with major psychiatric disorders such as schizophrenia and bipolar disorder, the researchers note. Telomeres are also highly sensitive to environmental and lifestyle factors, including possible dietary influences, prompting scientists to explore whether coffee might affect the rate at which telomeres shorten in people with severe mental ill health.

The researchers analysed data from 436 adult participants enrolled in the Norwegian Thematically Organised Psychosis (TOP) study between 2007 and 2018. Of these, 259 participants were diagnosed with schizophrenia, while the remaining 177 had affective disorders, including bipolar disorder and major depressive disorder with psychosis. Participants were asked how much coffee they consumed each day and were categorised into four groups: non-drinkers; those consuming one to two cups; those drinking three to four cups (110 participants); and those drinking five or more cups daily. They were also asked about smoking habits and the duration of tobacco use.

Participants who drank five or more cups of coffee per day were significantly older than those who drank either none or one to two cups. Additionally, individuals with schizophrenia reported drinking significantly more coffee than those with affective disorders. Smoking emerged as a major confounder in the analysis. Smoking is known to increase caffeine metabolism, and around 77 per cent of all participants were smokers, having smoked for an average of nine years. Those drinking five or more cups of coffee daily had smoked for significantly longer than participants in the other groups.

Telomere length was measured from white blood cells extracted from blood samples using quantitative polymerase chain reaction. The results revealed a significant difference in telomere length across the four coffee-consumption groups, forming a J-shaped curve. Compared with those drinking no coffee, participants who consumed up to three to four cups daily had significantly longer telomeres. However, this benefit was not observed in participants who consumed five or more cups per day.

After adjusting for age, sex, ethnicity, tobacco use, type of mental illness and psychotropic drug treatment, the researchers found that participants drinking three to four cups daily had telomere lengths comparable to individuals who were biologically about five years younger than non-coffee drinkers. This suggests that moderate coffee intake may slow the pace of cellular ageing in people with severe mental illness.

The global popularity of coffee further strengthens the public health relevance of these findings. An estimated 10.56 billion kilograms of coffee were consumed worldwide in 2021–22 alone, underlining how deeply embedded coffee is in daily routines across cultures. Yet the researchers cautioned that while moderate consumption may be beneficial, excessive intake could reverse these gains. As they warned, “Consuming more than the daily recommended amount of coffee may also cause cellular damage and TL shortening through the formation of reactive oxygen species,” emphasising that international health authorities recommend limiting caffeine intake to a maximum of 400 mg per day, roughly equivalent to four cups of brewed coffee.

Limitations of the study

Despite its promising findings, the study has several important limitations, some of which the researchers themselves acknowledged. One of the primary weaknesses relates to how coffee consumption was measured. As stated by the authors, “One of the main limitations of our study was the robust measurement of coffee consumption. The current self-report data inquired only about the number of cups of coffee ingested per day, and not the time of day consumed or instant versus filter coffee, which have been shown to influence the link between coffee consumption and health.”

Also, as the researchers noted, this is an observational study and therefore does not establish a direct cause-and-effect relationship. However, they propose plausible biological mechanisms that could explain the association. Coffee is rich in powerful antioxidant and anti-inflammatory compounds that may protect cells from oxidative stress and chronic inflammation, two processes known to accelerate telomere shortening and biological ageing.

In their own words, the researchers stated, “Telomeres are highly sensitive to both oxidative stress and inflammation, further highlighting how coffee intake could help preserve cellular in a population whose pathophysiology may be predisposing them to an accelerated rate of ageing.”

The study also did not account for other sources of caffeine, such as tea, energy drinks or soft drinks, nor did it measure the actual caffeine concentration in each cup of coffee consumed. Different caffeine sources and strengths could produce varying effects on telomere biology. Moreover, while the authors speculated that the observed increase in telomere length might be driven by coffee’s antioxidant and anti-inflammatory properties, they did not directly measure inflammatory markers or antioxidant levels in participants’ blood.

Another limitation lies in medication data. Although psychotropic medication use was recorded, the study did not account for other commonly used drugs for physical illnesses such as beta-blockers, statins or metformin, which may independently affect inflammation, metabolism and biological ageing. This leaves open the possibility that unmeasured pharmacological factors could have influenced telomere length.

The study population consisted solely of psychiatric patients with affective disorders or schizophrenia and did not include a healthy control group for comparison. This limits the ability to directly compare telomere dynamics between psychiatric and non-psychiatric populations. Additionally, the study was cross-sectional in nature, capturing a snapshot in time rather than tracking changes in telomere length over years. As a result, it cannot establish whether coffee consumption truly slowed telomere shortening over time or whether individuals with longer telomeres were simply more likely to consume moderate amounts of coffee.

Telomeres were assessed using a technique that provides an average telomere length but does not quantify the number of critically short telomeres, an important predictor of cellular ageing and disease risk. Measuring critically short telomeres might have offered additional insights. Furthermore, telomere length was the only marker of biological ageing included in the study. Ideally, multiple indicators such as epigenetic clocks or brain age measures would have provided a more comprehensive assessment of biological ageing.

What experts say

Dr Nimesh Desai, Senior Consultant Psychiatrist and Psychotherapist and former Director of the Institute of Human Behaviour and Allied Sciences (IHBAS), emphasised the distinction between association and causality in medical research. He noted that “mere association is not any indication of causality. Or even a contribution. There are at least three levels involved: a statistical finding of association, some contribution of that factor, or causality. This study is about association.”

He drew a parallel with earlier research on alcohol, explaining that “in the 1980s, Americans conducted research suggesting that one or two glasses of wine daily could improve heart health. Some misread this as, even if you don’t drink, you should start drinking. This makes no sense. It only applied to those who were already drinking moderately, compared to those drinking less.”

Dr Desai also cautioned against misinterpreting findings in cultures with high caffeine consumption. He said, “Across humanity, and certainly in some hard-driven cultures, tea and coffee addiction, or even overdose, is quite common. We don’t want that.”

Commenting on the limitations of the study, he added, “The researchers have stated the limitations, but often, when findings are published, readers may not focus on these cautions, which can lead to misleading interpretations.”

Dr Desai further noted that “the authors suggested that telomere length might be influenced by coffee’s antioxidant and anti-inflammatory properties. But they did not directly measure inflammatory markers or antioxidant levels in participants’ blood, so we must interpret these findings carefully.”

Also read: FACT CHECK: Is black coffee good for health?