Mediating depression through the Mediterranean Diet

Depression and cardiovascular disease (CVD) may not seem to have much in common. At first glance, it’s clear that the former is a disabling mood disorder, often treated by psychotherapy and/or drug therapy, while the latter refers to a group of diseases involving the cardiovascular system, where the focus is largely on prevention through lifestyle. But if there is an overlap, it would certainly be worth knowing about. Depression affects about four percent of the world population and is the second leading cause^[1] of years lost to a disability. On the other hand, CVD is the leading cause of death in the world. If there is a common link, it’s possible that a single intervention could impact both conditions, which in turn could impact a lot of people’s lives.

On closer inspection, there is indeed some overlap between the two, as shown in Figure 1. Observational evidence has found that having CVD is associated^[2] with an increased likelihood of having or developing depression, and vice-versa. These associations could be explained^[3] by the role of inflammation in both CVD and depression^[4]. Notably, one study^[5] found that serum concentrations of omega-3 fatty acids, which play a largely anti-inflammatory role in the body, were lower in people with heart disease with depression compared to people without depression.

The role of inflammation in depression is further supported by the hypothesis that antidepressant drugs exert some of their effects by modulating inflammation^[6]. However, they are often accompanied by several side effects^[7], including weight gain, sexual dysfunction, and suicidal thoughts^[8]. A practical intervention that mimics the beneficial effects of antidepressant drugs, accompanied by fewer side effects, would be useful.

Meta-analyses of observational studies have shown^[9] that “healthy” dietary patterns rich in fruit, vegetables, fish, and whole grains, such as the Mediterranean diet^[10], are associated with a lower risk of depression. Intervention studies have demonstrated that a Mediterranean diet reduces inflammation^[11] and the risk of CVD.

A previous randomized trial investigated the Mediterranean diet in adults with high CVD risk and found a trend towards a reduced risk of depression. However, that study had a small sample size and was not investigating depression as a primary outcome. Another RCT also found that a dietary intervention improved mental health. The study under review was designed to test whether a nutritional intervention confers any benefits on symptoms of depression and had a larger sample size designed to find an effect for this outcome.

Inflammation is a common risk factor for depression and CVD. Observational research has associated a Mediterranean dietary pattern with a reduced risk of both, and interventions further support a protective role of the Mediterranean diet in CVD development. However, interventions in people with depression are lacking. The study under review sought to investigate whether a Mediterranean diet could affect depressive symptoms.