Mental health disorders including depression, schizophreniaand anorexia show links to biological markers detected in routine blood tests, according to our new studio of genetic, biochemical, and psychiatric data on nearly a million people.
The research will increase our understanding of the causes of mental illness and may help identify new treatments.
Healthy body healthy mind
People often think of mental health as separate from the health of the rest of the body. This is far from certain: there is clear evidence that many biochemicals are involved in diseases such as diabetes and autoimmune conditions directly impact the function of our brain.
Many studies have tried to address this by focusing on substances called biomarkers that can be easily measured in the blood.
A biomarker is simply something in the body that is a sign of a particular disease or condition. These are often related to the kinds of things reported in a blood test ordered by your doctor, such as cholesterol, blood sugar, liver enzymes, vitaminsor markers of inflammation.
Biomarkers found in routine blood tests are helpful, as they are often affected by diet and lifestyle, or drug treatment.
The complex role of genetics in mental health
It is often difficult to study the role of these blood biomarkers in mental health conditions. Many studies in this area are often not large enough to draw strong conclusions.
One solution is to look at genetic influences on both mental illness and measured substances in the blood. Genetics is helpful as we now have data on millions of people who have volunteered for research studies.
Both mental illness and blood biomarkers are what geneticists call “complex traits“. In complex traits, many genes are involved and environmental factors also contribute.
The widespread availability of genetic data has allowed us to investigate how large numbers of small DNA sequence changes (or “variants”) relate to risk of mental illness. These same variants can also be linked to measured levels of a biomarker in the blood.
For example, a variant in a particular gene may increase the risk of developing schizophrenia and may also be linked to decreased levels of a vitamin circulating in the blood.
Most of these variants are individually associated with very small changes in something like mental illness risk, but can add up to produce larger effects.
How are blood biomarkers related to mental illness?
Our recent study sought to use genetics to investigate the relationship between nine mental health disorders and 50 factors measured in routine blood tests, such as cholesterol, vitamins, enzymes, and indicators of inflammation.
We use data from very large studies done by other people, with data from almost a million volunteers included in total.
Our study first confirmed the existence of what is called genetic correlation between blood biomarkers and mental illness, which was more widespread than previously shown.
Genetic correlation means that the effect of DNA sequence changes on mental illness risk and levels of a given biomarker were more similar to each other than would occur by chance alone.
To take an example, there was a positive genetic correlation in our study between white blood cell count and depression. This could indicate that some process in our body influences both depression and white blood cells.
If we could identify what this shared process is, it could lead to a better understanding of the causes of depression and this could be targeted for treatment.
Correlation versus causation
Our study showed that there correlation between the genetics of mental illness and factors in the blood, but this doesn’t tell us if blood biomarkers are involved in what Causes Mental illness.
To distinguish correlation from causation in medicine, the gold standard approach is to perform clinical trials where patients randomly receive a treatment or a placebo. However, these assays are expensive and difficult to perform.
We did the next best thing: use DNA variants linked to changes in blood biomarkers to act as a nature clinical trial. This process takes advantage of the fact that we randomly inherit DNA variants from our parents, in the same way that participants in a clinical trial are randomly given a treatment or a placebo.
It is a complex method and the results need careful interpretation.
We found evidence that some substances measured in the blood may be involved in causing some mental illnesses. Proteins related to the immune system, for example, may be involved in depression, schizophrenia, and anorexia.
More work is now needed to identify how precisely these blood measurements are involved in these disorders and to find out if they can be treated.
William KingPostdoctoral Research Fellow, School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle, NSW, Australia, University of Newcastle.
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