Mental health is a priority for the World Health Organization and it is no wonder. Depression is the leading cause of disability worldwide, affecting over 350 million people. A wide range of people suffer from depression; however, it does affect more women than men (1). Prescription medications for depression are effective about 54% of the time; whereas, placebos are effective 37% of the time (2). Recently both the effectiveness and safety of antidepressants have come into question, spurring research into other potential treatments.
One option is an omega-3 polyunsaturated fatty acid (n-3 PUFA) supplement (3). Over time our diet has shifted away from fish, wild game, wheat germ and walnuts – foods high in omega-3 fatty acids – towards a diet that is higher in omega-6 rich vegetable oils. Does an omega-3 deficient diet increase the risk of depression? If yes, can we reverse the effects through dietary changes or supplements?
PUFAs and the Brain
Polyunsaturated fatty acids (PUFAs) include both omega-3 and omega-6 fatty acids. These fatty acids are considered essential because the body cannot make them so they must come from the foods we eat. They have several important roles in the brain including: acting as messengers, aiding neuron formation, and mediating the receptors for serotonin, norepinephrine and dopamine.
The ratio of omega-3 fatty acids to omega-6 fatty acids is important in all of these processes. The “Western diet” has a resulted in an increase in the proportion of omega-6 fatty acids upsetting this balance (3). Hypothetically, this shift could promote changes in the body that increase the risk for depression.
Low n-3 PUFA Diets and Rates of Depression
Do diets that are low in omega-3 fatty acids increase the risk of depression? Frustratingly, the evidence seems to be almost evenly split with four studies finding that diets high in omega-3 fatty acids resulted in lower rates of depression and three studies reporting no difference (3). It has been suggested that the effects may be gender dependent with lower rates in females consuming a diet high in omega-3 fatty acids but no effect on males (3,4).
Another way to determine if omega-3 fatty acids are related to depression is to look at actual levels in the blood rather than diet records. Here no link between PUFAs and depression was observed; however, this was a non-clinical population and did not include people with severe depression. Furthermore, the omega-3 intakes in general were quite low, so it is possible no one was consuming enough omega-3s to have an effect (3, 5).
To try to clarify the relationship, other studies have looked at the omega-3 intake of people and then followed them overtime to see if they develop symptoms of depression. Two studies report lower rates of depression in those that consumed a diet high in fish and/or other omega-3s (6, 7).
Importantly, there is a concern regarding the mercury content of some fishes, in which case there may be an increase in mental disorders (3). Health Canada’s report on the mercury content of fish can be used to select the healthiest options.
Evidence from studies looking at omega-3 intakes in large groups of people is conflicting but what about clinical trials where people are given supplements and compared to placebo groups?
In individuals with major depressive disorder (MDD), most of whom were already taking antidepressants, six studies found the n-3 PUFA supplements were more effective than a placebo; whereas, seven studies found no effect (3). Young healthy people taking an n-3 PUFA supplements reported increased feelings of vigor and reduced anger, anxiety, fear, depression, and confusion (8,9). Conversely, another study reported less fatigue but no differences in depression (10).
Stress and n-3 PUFAs
Generally, the evidence is conflicting regarding the effectiveness of n-3 fatty acids on reducing the symptoms of depression. It may be that there is significant individual variation or that other factors including medications, age, gender, etc. are muddying the waters. If there is a link between n-3 PUFAs and depression it may be STRESS. Stress ,as well as a diet high in omega-6 fatty acids increase inflammation in the body, which is positively correlated to depressive symptoms (3). Stress increases heart rate, blood pressure, cortisol, and epinephrine; whereas, omega-3 fatty acids reduced the cortisol and epinephrine response to stress (11).
No Baloney’s advice? At present, the scientific research is conflicted regarding the potential benefits of omega-3 fatty acids on depression. Numerous questions remain:
- Who is most likely to benefit, if anyone.
- If omega-3 supplements are effective, what is the optimal dose?
- Are they effective on their own or perhaps only in conjunction with other antidepressants?
- What are the effects on other disorders often associated with depression such as anxiety, stress, etc.?
With this in mind, it would be premature to recommend supplements BUT given the other health benefits, everyone should try to meet the recommendation of two servings of fish per week!