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Ageing: Live faster, die younger

People with schizophrenia show signs of accelerated ageing — a phenomenon that could lead researchers to a deeper understanding of the disease.

For decades, evidence has suggested that people with schizophrenia have shortened lifespans. In the early twentieth century, doctors observed that these patients tended to die younger and seemed less healthy than other patients in the same psychiatric hospitals. And today, schizophrenia patients appear to suffer from heart, lung and metabolic problems at a disproportionate rate — and at startlingly young ages.

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There are plenty of potential culprits: suicide, for example, along with the negative side effects of antipsychotic medications, substance abuse, smoking and poor health care — any one of which could explain why people with schizophrenia die 15–25 years earlier, on average, than those in the general population.

But some researchers believe that these external factors do not fully account for the reduced longevity. They point out that the increased mortality among schizophrenia patients predates the widespread use of antipsychotics, encompasses diverse causes of death, and has been documented even among patients who are receiving high-quality medical care. These observations have led several investigators to propose a new explanation for the early deaths of those with schizophrenia: the ageing process itself speeds up. “Our hypothesis is that one of the reasons that they die younger is because they get old faster than the general population,” says Brian Kirkpatrick, a psychiatrist at the University of Nevada School of Medicine in Reno.

Accelerated ageing, Kirkpatrick and several other scientists say, may be a fundamental part of the schizophrenia pathology. This belief is supported by numerous studies of physiological, neurological and cognitive abnormalities in people with the disorder. Researchers are now trying to determine precisely how schizophrenia and ageing are related. They hope that fresh insights into the disease will help people with schizophrenia stay healthy longer, and possibly even point the way to better treatments.

Marking time

As there's no definitive test or biomarker for ageing, proponents of the accelerated-ageing hypothesis have been gathering support for their idea by piecing together a diverse array of research findings.

For example, scientists and doctors have noticed that several ailments associated with ageing, including type 2 diabetes and cardiovascular disease, are more common among people with schizophrenia (see 'Schizophrenia's health burden'), and appear earlier in life, than in the general population. The trouble is that antipsychotics commonly prescribed for schizophrenia can lead to weight gain and increase the risk of diabetes. So to control for these effects, studies need to focus on patients who have recently been diagnosed with schizophrenia and have not yet started taking medication.

Several studies of these antipsychotic-naive patients have found that impaired glucose tolerance — a condition sometimes called prediabetes that is a risk factor for heart disease — is more common among patients with schizophrenia than in the general population1. These results suggest that schizophrenia is associated with abnormal glucose metabolism, and that it is not solely a side effect of medication.

Kirkpatrick has also examined antipsychotic-naive patients for other signs of premature ageing. In 2009, his team showed that these patients have an increased pulse pressure, a calculation of the difference between systolic and diastolic blood pressure2. In general, pulse pressure increases with age and is a predictor of heart disease. And in 2011, Kirkpatrick's team showed that antipsychotic-naive men with schizophrenia have lower levels of testosterone, a hormone that declines gradually with age, than age-matched controls3.

There are tantalizing signs in the genes, too. Telomeres, the DNA tails attached to the end of chromosomes that shorten each time a cell divides, are often used as a marker of biological ageing. Several small studies have documented shorter telomeres in patients with schizophrenia, but a larger 2013 study failed to replicate these results — in fact they found longer telomeres in people with the disease4. These apparently contradictory results are confounded by the fact the studies used different methodologies and examined different populations, ranging from antipsychotic-naive patients to those who have had poor responses to the drugs.

Cognitive studies provide firmer support for the idea of accelerated ageing. Patients with schizophrenia seem to exhibit a premature deterioration in cognitive function, says Philip Harvey, a psychologist at the University of Miami Miller School of Medicine in Florida. Working with Christopher Bowie, a psychologist at Queen's University in Kingston, Ontario, Canada, Harvey tested processing speed and episodic memory — two areas of cognitive functioning that tend to worsen with age — and found that people with schizophrenia perform like subjects who are decades older5.

The reason for this decline could be physiological. The brain contains grey matter, comprising neurons, and white matter, made up of axons — the cellular projections that transmit signals between neurons. “As we age, we tend to lose our white-matter integrity,” says Peter Kochunov, a psychologist at the Maryland Psychiatric Research Center at the University of Maryland in Catonsville. “The reason the brain slows down with age is because of this loss.”

Kochunov and his colleagues have examined white matter using diffusion tensor imaging, which measures the movement of water in the brain. (Water molecules tend to travel down the length of an axon.) They found that people with schizophrenia lose white-matter integrity at nearly twice the rate of controls6. “This is kind of alarming because in normal ageing, the loss of integrity is linked very strongly with basic cognitive domains such as processing speed,” he says. And the white-matter loss is specific to schizophrenia: Kochunov's team did not find such rapid deterioration in people with major depression, another diagnosis associated with increased mortality and an elevated risk of a variety of ageing-related disorders.

Five-year plan

The evidence so far suggests a correlation between schizophrenia and ageing, but many of these studies were small and based on single observations of patients and controls. Confirming the findings will mean following larger groups of subjects for many years, says Dilip Jeste, a psychiatrist and neurologist at the University of California, San Diego.

In 2012, Jeste began a five-year longitudinal study of accelerated ageing, enrolling more than 250 adults from 26 to 65 years of age, including individuals with and without schizophrenia. Each year, the researchers administer a battery of medical tests. For instance, they look for signs of inflammation and oxidative stress, which occurs when highly reactive, potentially damaging oxygen compounds flood the body's cells. Both inflammation and oxidative stress tend to increase with age and are associated with a variety of chronic diseases. They have also been linked to neurodegeneration and proposed as factors that might contribute to schizophrenia.

“If schizophrenia is associated with accelerated ageing, you would expect the shortening of telomeres to be faster.”

In addition, Jeste's team will not only measure telomeres but also record their rate of shortening over time. “If schizophrenia is associated with accelerated ageing, you would expect that the shortening of telomeres over the five years in schizophrenia would be faster than that in healthy comparison subjects,” he says.

The scientists will also collect data on potentially confounding variables, including medications, substance use, smoking history and diet. They hope the results will show whether widespread accelerated ageing really does occur in patients with schizophrenia, and whether the phenomenon is an intrinsic part of the condition or a result of lifestyle and demographic factors that accompany it.

Cause or effect

If Jeste's study supports the accelerated-ageing hypothesis, the next step will be to investigate how and why it occurs. Schizophrenia itself might cause accelerated ageing, but maybe some other factor, such as oxidative stress or inflammation, predisposes individuals to both conditions. Moreover, Kirkpatrick says, environmental stresses and exposures in utero may predispose people to both schizophrenia and accelerated ageing. The explanations are not necessarily mutually exclusive, and it's not yet clear whether a single biological process is responsible. “I think several different mechanisms are likely to be involved,” Jeste says.

Identifying the physiological mechanisms that contribute to both ageing and schizophrenia could suggest new drug targets for schizophrenia. Confirming that oxidative stress is a common factor, for instance, could mean that antioxidant medications could help alleviate the symptoms of schizophrenia. “It will also be interesting to look at other disease models that have accelerated ageing, or are at least ageing-related, and seeing whether some of the treatments in these could be applied in schizophrenia,” says Bowie.

What started as a curious observation now has the potential to add to the understanding of a complex chronic disease and could help doctors improve the quality of life for people with schizophrenia. “These folks are dying young — that's important,” Kirkpatrick says. “If we understood it better, perhaps we could help them.”

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Anthes, E. Ageing: Live faster, die younger. Nature 508, S16–S17 (2014). https://doi.org/10.1038/508S16a

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