Drinking four cups of coffee a day could add years to your life, new research today suggested. 

Coffee has long been associated with a lower risk of heart disease, dementia and diabetes but now a new study has found that coffee can help people battling poor mental health live longer, adding five years to their life compared with non-coffee drinkers. 

Patients with severe mental disorders (SMD), such as schizophrenia and bipolar disorder, tend to live 15 years less than their mentally healthy peers, with SMDs having been linked with heart disease, certain cancers and advanced aging. 

But in a first-of-its kind study, published by the British Medical Group, researchers found that coffee had a lengthening effect on SMD patients' telomeres—the caps on the end of chromosomes that protect the DNA from damage—giving them the equivalent of five extra years. 

But only if they drank between three and four cups a day. 

Drinking more than this, the maximum daily intake recommended by several international health authorities including the NHS and the US Food and Drug Administration (FDA), had an adverse affect, shortening telomeres and lifespan. 

Experts think telomeres, which seem to be shorter in SMD patients, respond to environmental factors including diet, prompting researchers to explore whether coffee might influence the rate at which they shorten in mentally ill people. 

In the study, researchers analysed blood samples from 436 participants diagnosed with schizophrenia or affective disorders including bipolar and major depressive disorder with psychosis from the Norwegian Thematically Organised Psychosis study. 

Participants between 18 and 65-years-old were recruited from four psychiatric units across Oslo between 2007 and 2018 and interviewed about their current coffee consumption: no coffee, 1-2, cups, 3-4 cups, and five or more. 

Just 44 participants reported no coffee consumption. 

Similarly, clinical interviews aimed to establish smoking habits.

On average, participants who drank five or more cups a day were significantly older and had smoked for significantly longer than those who drank none or very little. And those with schizophrenia also tended to drink more than those with an affective mood disorder. 

Telomere length was measured from white blood cell called leucocytes, extracted from blood samples, which revealed a significant difference among the four groups, forming a J shaped curve.

They found that compared to non-coffee drinkers, drinking around three to fours cups a day was associated with longer telomeres, but not in those drinking five or more cups a day. 

The researchers concluded: 'Based on an average of 70-base pair reductions per year, this represents five years younger biological age in the coffee-drinking group.' 

The findings from the new study could also lead to similar research into the effect of coffee on the telomeres of people who do not currently live with a mental health diagnosis. 

Exactly why coffee has such effects remains unclear, with some studies pointing to caffeine whist others highlight its high polyphenol content, but this study focused on its antioxidising properties. 

'Coffee has been noted to contain several bioactive compounds, such as chlorogenic acid (CGA), cafestol, kahweol, trigonelline and melanoidins, all of which possess potent antioxidant properties.' 

CGA and other compounds found in coffee have been credited with the formation of pro-inflammatory cytokines, which help reduce inflammation—a common pathophysiological feature found in SMD. 

This, the researchers say, could highlight the 'potential protective effects that coffee could have in this population.' 

They added: 'Telomeres are also highly sensitive to both oxidative stress and inflammation, further highlighting how coffee intake could help preserve cellular ageing in a population whose pathophysiology may be predisposing them to an accelerated rate of ageing.' 

However, despite the potential benefits of coffee, consuming more than the daily recommended amount has also been linked to cellular damage. 

Dr Elizbeth Akam, a senior teaching fellow in biosciences at Loughborough University, who wasn't involved in the study, cautioned that to establish a true link between coffee and longevity, researchers need to consider the different compounds in coffee, such as caffeine, in the blood.

She said: 'A noteworthy limitation of this study is that it treats 'coffee' as if it were a single substance. 

'However, coffee contains many different compounds, and we don’t know which of these were administered, in what doses, or how much actually ended up in the bloodstream.' 

She added that the evidence in this area is a 'mixed bag' because patients self-reported their coffee consumption which could alter the efficacy of they study. 

'This matters because caffeine itself has been linked to telomere shortening.

'Future studies that measure the antioxidant capacity of the blood as whole could provide more effective details in terms of aging and health benefits.' 

It comes after a report revealed 20-somethings are facing a surge in rates of depression, anxiety and bipolar disorder. 

Data suggests the rise of mental health issues in the young is a recent phenomenon.

Overall, 34 per cent of young people now suffer symptoms of a mental illness, such as depression.