Depression is a common disorder that is likely to have many different causes. Studies have shown that some, but far from all, people with depression have elevated inflammatory markers. Researchers Klara Suneson and Daniel Lindqvist have been looking for answers to a specific question: can omega-3 containing high levels of fatty acid EPA (eicosapentaenoic acid) improve symptoms of depression when the patient also has inflammation in their body?
“We are talking about low-grade chronic inflammation of the type individuals often don’t notice themselves. The exact cause of low-grade inflammation is not clear, but there are many factors that can have an impact, such as a range of co-morbidities including rheumatism, obesity, sedentary behaviour, smoking and an unbalanced diet,” says Klara Suneson, who recently completed her doctoral thesis in psychiatry at Lund University and is a psychiatry resident at Region Skåne.
The results, which form part of Klara Suneson’s thesis, have now been published in the journal Brain, Behavior, and Immunity. Klara Suneson says that historically, researchers have often compared depressed patients with people who were not depressed, but she emphasises the importance of comparing different groups of people with depression instead.
“Patients with depression constitute a very heterogeneous group. One might be on sick leave, while another works full-time and drives the children to football practice. Not everyone becomes sick for the same reason, and therefore they won’t respond to the same type of medical treatment. That is why it is so important to identify biological markers of treatment response, such as inflammation,” says Klara Suneson.
Innovative study design
Daniel Lindqvist is a senior lecturer and associate professor at Lund University with a focus on biological and precision psychiatry. He is also a consultant in psychiatry for Region Skåne, and he agrees with his research colleague:
“Almost all previous studies have included depressed patients solely on the basis of the traditional diagnostic criteria. As Klara says, this is a very diverse group, and there is reason to believe that different treatments will work for different patients. Therefore, the overall impact of treatment in a study may appear weak and the treatment be rejected – even if it could help in a subgroup.”
The design of the study is innovative in that we hypothesized that only those with depression chronic low-grade inflammation would respond to omega-3.
In the current study, 101 patients were divided into several different groups based on the degree of inflammation in blood samples. To take part in the study, the patients had to have previously tried antidepressants for at least six weeks without success. There was no placebo group – even participants without inflammation were given omega-3 for eight weeks. The dose was relatively high, two grams of EPA per day (compared to less than one gram, which is often the recommended daily dose on bottles of omega-3 pills). The EPA dose was given in addition to standard antidepressant treatment. In the group with the highest levels of inflammation, there was no improvement following omega-3 supplementation. However, for the group with mild to moderate elevations of inflammation markers, the difference was clear.
“We saw a significant improvement, both when we made an expert assessment based on 17 questions about depression and when the participants self-rated their symptoms of fatigue and sleep problems,” says Klara Suneson.
Previous studies have not been able to show a robust antidepressant effect of omega-3 – but in most of those studies the inflammation pathway was not specifically investigated.
The researchers at Lund are now faced with new questions that require further research: Among those who responded to omega-3 – will their depression return if they stop taking the supplements? And, as eight weeks is quite a short time, could their symptoms further improve if omega-3 is given a longer period?
“Also, what happens if the dose is increased further? Could omega-3 help those with high levels of inflammation, too? We’ll have to see if we or other researchers investigate this further,” says Daniel Lindqvist.
