A new large review of the scientific evidence suggests that most dietary supplements don’t do much to help people suffering from mental health disorders.
Supplements are often touted as something like a shortcut to a healthy body and mind, though evidence for that rosy view is lacking. Researchers in Australia took a deep dive into the medical literature to see what they could find about supplements and mental health.
Their review, published in the journal World Psychiatry, is a meta-analysis of 33 other meta-analyses published since 2012, which looked at randomized, controlled clinical trials of people taking supplements to treat symptoms of depression and other mental illnesses. All told, the trials included more than 10,000 patients, who often took the supplements alongside standard treatments. These supplements included vitamin B9, otherwise known as folic acid, omega 3 fatty acids, minerals like zinc or magnesium, and amino acids like N‐acetylcysteine (NAC) and glycine.
They ultimately found that supplements were safe to take and not likely to interfere with existing psychiatric medications. But many of the interventions tested, such as taking magnesium for depression or folic acid for schizophrenia, didn’t have significant evidence for their benefits. In other cases, such as taking NAC for depression symptoms, the evidence was positive but based on very small trials.
That said, there were situations where the positive evidence was compelling and merited further study, the authors said.
This was most apparent with taking omega-3s to supplement treatment for major depression; they might also have a small effect on relieving symptoms of ADHD. Some decent evidence showed that NAC could boost the benefits of standard treatments for mood disorders and schizophrenia. And there was also evidence that taking methylfolate—the byproduct of folic acid that our bodies actually use—could be useful as an add-on treatment for schizophrenia and depression. Methylfolate is already offered as a prescription medical food for people with treatment-resistant depression who are deficient in it.
“Although the majority of nutritional supplements assessed did not significantly improve mental health outcomes beyond control conditions, some of them did provide efficacious adjunctive treatment for specific mental disorders under certain conditions,” the authors wrote.
The findings, mixed as they are, should be seen in a positive light, according to study author Joseph Firth, a senior research fellow at Western Sydney University’s National Institute of Complementary Medicine.
“While there has been a longstanding interest in the use of nutrient supplements in the treatment of mental illness, the topic is often quite polarizing, and surrounded by either over-hyped claims or undue cynicism,” Firth said in a statement released by the university. “This mass of data has allowed us to investigate the benefits and safety of various different nutrients for mental health conditions—on a larger scale than what has ever been possible before.”
In addition to quantifying how effective some supplements can be for certain groups, Firth and his team said, there needs to be work done on figuring out why exactly they’re helpful.
People who have major depression, for instance, are sometimes deficient in methylfolate—often due to a genetic mutation that makes it hard for them to convert folic acid to methylfolate. Without enough methylfolate, these people are then less able to produce serotonin and other neurotransmitters important for proper mental functioning. There might very well be similar explanations for why the lack of certain nutrients is crucial to the development of mental illness in some people.
These explanations could also involve the gut microbiome—the teeming microbial environment that lines our digestive system. The gut has garnered more and more attention for its role in our physical and mental health in recent years, since it “talks” regularly with our brain. And many researchers now believe that the microbiome needs to be balanced for this line of communication to be healthy. For the time being, the authors noted though, there’s less evidence looking into whether probiotics and prebiotics—supplements loaded with “good bacteria”—can effectively help people with mental illness.
It’s also important to caution that anyone taking supplements should ideally consult their doctor first, since some can interfere with certain medications or medical tests. Experts generally recommend that people stick to single-ingredient supplements (rather than multivitamins), since those are less likely to contain useless, undisclosed, or potentially dangerous ingredients.