According to over three decades of research, depression can predict the development of heart disease. Conversely, say researchers from Granada University, a high risk of heart disease can cause this mood disorder — each one amplifying the risk of the other.

Which came first, depression or heart disease?

The new study, published in PLOS ONE, involved men and women at risk of heart disease. The researchers basically tracked the effects of a Mediterranean diet on depression and cardiovascular disease. After six years, results from participants across Spain indicated that participants with the highest cardiovascular risk suffered the most depression, which was reversed over time by key lifestyle choices.

Experts have known for some time that when people have heart disease, they are far more likely to suffer an adverse cardiac event such as a heart attack or blood clots if they have depression. In some cases, depression during cardiovascular events can even lead to death, as a past study from the Intermountain Medical Center showed in 2017. The 2017 study (based on 25,000 patients diagnosed with heart disease) showed that participants were twice as likely to die if they developed a depressive illness. The authors of that study noted that participants “need to be continuously screened for depression, and if found to be depressed, they need to receive adequate treatment and continued follow-up.”

Many papers have gone on to show that depression is now the strongest predictor of death in the first ten years after the diagnosis of cardiovascular disease, but we’re still not entirely sure why. A possible reason for this fact could be that depression increases platelet reactivity and proinflammatory markers – all risk factors for cardiovascular disease. And according to the (National Institutes of Health) NIH, in a causal two-way link, at least a quarter of cardiac patients suffer from depression. Conversely, adults suffering from depression can develop heart disease in only a small number of cases.

Using the treatment of depression to prevent heart disease

The authors of the 2017 study also highlight how patients’ lifestyle choices such as a bad diet, smoking, a lack of exercise, or alcohol can influence the development of both illnesses, which makes sense as they’re very closely linked.

“We are confident that depression is an independent risk factor for cardiac morbidity and mortality in patients with established heart disease,” said Professor Robert Carney from Washington University School of Medicine, commenting at the time. “However, depression is also associated with other risk factors, including smoking, so it can be difficult to disentangle its effects from those of other risk factors.”

But as experts suspect that multiple pathways are involved in these illnesses establishing a definitive cause-effect link between depression and heart disease has proved trying- basically, evidence showing that treating depression reduces the risk of future heart disease is needed here.

In simple terms, scientists should use a randomized trial where eligible participants are chosen at random and compared to a control group of healthy people here.

In this case, both groups get the same treatment, evaluating whether alleviating depression can prevent heart disease, so patients at risk of developing a heart condition rather than those who have already had cardiovascular disease will be the eligible parties here.

Experts hope these trials will enable clinicians to treat depressive illnesses to prevent heart disease, just as treating cholesterol or blood pressure is used to improve heart health. But randomized trials analyzing the potential impact of cardiovascular risk on developing depression have been scarce up until now. Studies like this could help paint a much more comprehensive picture of the interactions between various conditions.

Preventing heart disease and easing depression with diet

In a randomized trial, the newest study from Spanish researchers evaluated over 6,500 individuals aged between 55 and 75 years of age with no cardiovascular disease.

Firstly, the team used a special prediction model that estimates the likelihood of developing heart disease based on how many risk factors the patient has (like smoking cigarettes or drinking alcohol). Once the group had collated all the scores, they placed each person in either a low, medium, or high cardiovascular risk group.

From the onset, the data showed that women in the high-risk group were more likely to develop depression than women with a low risk of cardiovascular disease.

Additionally, participants in the medium and high-risk groups with a healthy level of cholesterol (below 160 mg/ml) had more cases of depression than the low-risk group. But participants with total cholesterol of at least 280 mg/ml in the same two groups had a smaller risk of developing depression than volunteers in the low-risk group.

In an attempt to counteract both the presence of cholesterol and depression, the team instructed participants to follow a Mediterranean diet encompassing foods such as whole grains, fruits, legumes, and nuts – thought to reduce the risk of depression and cardiovascular disease.

After two years on this diet, the team measured the patients’ cardiovascular and depression risk scores. Remarkably, all participants had decreased their depressive risk score, with the most significant drop witnessed in the medium and high-risk groups with high cholesterol levels.

With this in mind, the authors surmise they have shown that a high risk of cardiovascular disease is associated with depression, especially in women. And stress the importance of lifestyle factors such as a Mediterranean diet that patients could use to counteract both these conditions – but concede further trials are needed.

It’s also important for future studies to see what exactly is the causal nature of this interaction. Does one condition affect the other directly, do they have a common cause, or is it some other type of relationship? A recent analysis disproved a common hypothesis (that depression leads to cardiovascular disease by increasing blood pressure), suggesting that we’ve still yet to uncover the mechanisms at work.

Where to get help:

Many types of support are available for individuals recovering from serious cardiac events. These include cardiac rehabilitation, social groups, and treatment by mental health professionals – all of which have proven in trials to decrease bouts of depression to increase treatment outcomes for heart patients. For more resources and support, here are a few resources:

• The CDC page on heart disease and mental health disorders.
• The UK NHS page on finding depression support groups.
• The Cleveland Clinic page on depression and heart disease for more information.
• The Johns Hopkins page on depression and heart disease.