This series is intended to showcase the diversity of studies being conducted in a new, rapidly emerging field of nutrition and mental health, coined by leaders in the field as nutritional psychiatry (Sarris, Logan, et al., 2015). The series begins with an article by Sánchez-Villegas, Ruiź-Canela, Gea, Lahortiga, and Martínez-González (2016) that fits into the field of nutritional epidemiology but expands it significantly.
Over the past decade, there has been a steady increase in epidemiological studies investigating the relationships between dietary patterns and mental states. Both cross-sectional and longitudinal studies have shown that the more one eats a Western or highly processed diet, the more one is at risk for developing psychiatric symptoms such as depression and anxiety. Conversely, the more one eats a diet rich in fruits and vegetables, high in healthy fats, nuts, and fish, and low in processed food (a Mediterranean-style diet), the more one is protected from developing a mental disorder (Akbaraly et al., 2009; Jacka et al., 2010; Jacka et al., 2011; Sánchez-Villegas et al., 2009; Sánchez-Villegas et al., 2012).
In several studies, the dietary pattern has been shown to precede the onset of psychiatric symptoms, clearly supporting the direction of causality (dietary pattern does influence mental health, although we tend to attribute poor dietary patterns to being carbohydrate craving induced by low mood).
Sánchez-Villegas and colleagues broaden their analyses beyond the Mediterranean diet to Mediterranean lifestyle variables. What they report is of great relevance to our understanding of how lifestyle variables fit together: Dietary pattern, physical activity, and social activities were all independently and inversely associated with risk of depression. Taken together, the reduction in risk for those at the highest levels on all three variables was about 50%. If a drug with no side effects were to be associated with that significant a reduction in risk, it would be prescribed often. Is it time for our health professionals to prescribe Mediterranean diet, physical activity, and social activities?
Although some of the research in clinical patients involves intervention (changing dietary habits and examining associated changes in cognitive function and mental symptoms), other studies, such as the article by Chang, Jingling, Huang, Lu, and Su (2016) in the current series, evaluate correlations between some aspect of dietary intake in relation to mental health.
In a small group of 21 children diagnosed with attention-deficit/hyperactivity disorder (ADHD) and 21 non-ADHD controls, three types of variables were compared: n-3 fatty acid intake based on a food frequency questionnaire for the prior 3 months, the physical signs and symptoms known to indicate a deficiency in essential fatty acids (e.g., dry skin or hair, dandruff, brittle nails), and performance on some laboratory tasks of cognitive function and inhibition.
One intriguing finding was that although there were no group differences in omega 3 intake, there were group differences in signs of essential fatty acid (EFA) deficiency. Does this finding mean that children with ADHD might require more EFA intake than normal children to prevent signs of deficiency? This possibility does require further exploration but may tie into Bruce Ames’s hypothesis that some people may inherit an in-born error of metabolism that results in the need for a greater intake of the nutrient(s) not being well metabolized (Ames, 2004; Ames, Elson-Schwab, & Silver, 2002).
The study by Chang et al. also found that greater ADHD symptoms were correlated with lower n-3 fatty acid intake and higher severity of symptoms indicative of EFA deficiency. EFA deficiency was also correlated with higher delay aversion in the laboratory tasks of inhibitory control.
The series includes two articles that explore micronutrient treatment, one looking at a single nutrient (Sarris, Oliver, Camfield, & Dean, 2016) and one exploring the potential of multinutrient treatment (Lothian, Blampied, & Rucklidge, 2016).
When examining the potential of any new therapy, a question often emerges: Who might be most likely to benefit from this approach? Using data from a previously published clinical trial of N-acetyl-cysteine (NAC) in the treatment of obsessive compulsive disorder (OCD; Sarris, Oliver, et al., 2015), Sarris et al. asked whether there were any meaningful variables that predicted responsiveness to NAC. Their analyses uncovered the role of age, type of OCD, and duration of illness as potential moderators of treatment response. It is not surprising that the younger someone is and the shorter the duration of illness, the more likely one will respond to this one nutrient, advocating for early intervention as well as possibly using this approach before trialing medications. Certainly there is room for much greater exploration of determining who might benefit from directed nutrients: Epigenetic research and studies of biomarkers of inflammation may begin to illuminate this potential.
The article by Lothian et al. (2016) serves a dual purpose in this series. First, it introduces the use of broad-spectrum micronutrients (by which we mean having a large number of dietary minerals and vitamins) as a treatment modality for mental health problems. And second, it also displays innovations in the analysis of the data. Insomnia is an interesting symptom to target for treatment as it is associated with so many mental health problems, exacerbating them all.
Many other studies have shown alleviation of other psychological symptoms with micronutrient treatment: depression, anxiety, explosive rage, irritability (another symptom that crosses many diagnostic categories), and attentional problems (Rucklidge & Kaplan, 2013). So in that sense, this contribution, showing substantial improvements in sleep in this sample, adds to the growing evidence that many forms of psychological distress can be ameliorated by nutritional therapies. They also presented the data in an innovative way, using modified Brinley plots, to permit both idiographic individual and group outcomes to be evaluated concurrently.
There is an increasingly vast literature on mechanisms of action related to oxidative stress, mitochondrial dysfunction, gastrointestinal dysbiosis, and inflammation (Kaplan, Rucklidge, McLeod, & Romijn, 2015). In fact, our journey toward editing this special series began with our article published in this journal last year that attempted to present a simple explanation of how the framework that depends on these functions inevitably relates to nutrients and their critical role in health and disease.
The final article in the series, by Akbaraly and colleagues (2016), adds to the growing literature on mechanisms by providing some intriguing insights into the complex relationships among biomarkers and diets identified as being proinflammatory. In terms of epidemiologic findings, their data reinforce the relationship between dietary patterns and expression of depressive symptoms 5 years later (observed only in women, not men). But in addition, they describe the “dietary inflammatory index,” which was correlated at baseline with biomarkers of inflammation (CRP and IL-6). Perhaps surprising, these markers of inflammation did not influence the long-term association between the dietary inflammation index and recurrent depressive symptoms. Such a finding reinforces the complexity in understanding the role markers might play in the expression of illness. These relationships are not straightforward and require much additional research.
We hope this series brings further attention to this growing field of research. We are pleased to be a part of this new venture and hope that other scientists see the relevance to their own work.