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Psychosis is a scary word, conjuring images of people who have so lost touch with reality that they are unable to integrate with society. As with most everything else this condition exists on a continuum, mild symptoms may pose no problem for the sufferer1 nor be outwardly visible. Previous studies have seen correlations between the intake of polyunsaturated fatty acids (with the cute acronym PUFA2) and increased severity of psychotic symptoms, with this in mind a study was performed in Sweden looking at the dietary intake of fish and the incidence of psychosis symptoms in the general population.

In total 33,623 women completed the study which covered the period between 1991/92 to 2002/03 (with questionnaires at the beginning and end of this period). This group was then classified based on their answers to the questionnaires into 3 groups: Low, middle and high frequency of symptoms, where the low group included women with no symptoms. This gave a split of 18,411, 14,395 and 817 women in the groups respectively. The first question I had reading this study is how do you classify someone with psychotic symptoms? The women in the study completed two questionnaires to provide the information for this part.

The first was the Community Assessment of Psychic Experiences (CAPE, another cool acronym), this contained questions ranging from those looking at emotional states such as “Do you ever feel sad?”, to those that address personal perception like “Do you ever feel pessimistic about everything?”. Also included are the questions that we would more easily recognise as relating to psychosis such as “Do you ever feel as if a double has taken the place of a family member, friend or acquaintance?” or “Do you ever see objects, people or animals that other people cannot see?”.

There are also questions that might seem to generate positive answers from a wide range of the population that we would not consider psychotic such as “Do you ever think that people can communicate telepathically?”, a belief that if I can take what I see in the media seriously is becoming more widespread. And “Do you believe in the power of witchcraft, voodoo or the occult?” which thinking back to the furore that arose around the Harry Potter books is a view that is held by a disturbing number of people3.

Quite obviously simply answering affirmatively to these questions does not place you in the psychotic camp, it is the aggregate of these answers that matter as well as further variables that relate to these answers such as how these thoughts and experiences make you feel. The experience of seeing or hearing a loved one that has died is quite widespread but I don’t think general conclusions about the sanity of the general population can be reached using this information.

The second questionnaire was a variation on the Peters et al. Delusions Inventory (PDI, and the good acronyms come to an end). There is significant overlap between the questions asked in the PDI and the CAPE questionnaires, the main difference seems to be how each question is followed up. The CAPE approach simply asks how distressed the respondent feels if they answered affirmatively to a question (with a 4 point scale, Not distressed to Very distressed) while the PDI covers this aspect as well as asking how much the respondent thinks about it and how much they believe it is true.

Now how do the categories that I mentioned above (low, middle and high) relate to the results of the questionnaires? Rather than attempt to paraphrase the study I’ll just quote that bit:

“The “low level symptoms group” included women with no or few experiences of psychotic-like symptoms (≤3 “sometimes” and no “almost always” and “often” answers to any of the questions). The “high level symptoms group” included women with frequent experiences of psychotic-like symptoms (≥3 “almost always” or “often” answers). The “middle level symptoms group” was defined as participants not included in the low level or high level groups.”

Fairly simple, not as nuanced as I expect an in-depth psychological evaluation might be but that’s the limitation of performing a large scale study.

Finally, what were the results of the study regarding fish consumption and symptoms of psychosis? Interestingly the authors did not see a simple relationship between the two variables, there was no clear protective effect with increasing intake of fatty fish (those with high levels of PUFAs). Instead there was an optimal intake that was correlated with low (or no) symptoms, higher intake actually correlated with increased symptoms. The authors are unsure what could account for this effect stating:

“This puzzling finding may be due to unknown or known unhealthy constituents of fatty fish. For instance, environmental pollutants such as polychlorinated biphenyls (PCB) and dioxins are known to accumulate in fatty fish. Another possible explanation may be that the frequent intake of fish and PUFA may be advantageous in lower doses but disadvantageous in higher doses.”

The authors also caution that the study was not geared to determine a causal relationship between the variables merely how these were correlated4. Another interesting finding was that high levels of psychotic symptoms are also correlated with women who are both overweight and are smokers (and also for some reason migration to Sweden5).

Bottom line? Hard to say really, the results of this study are indicative but not definitive. The take home message in my book looks to be that it is a balanced diet which is most beneficial, including fish in your meals between 1 and 3 times a week or so. For those of us who aren’t keen on fish, supplements might be the answer but that’s really another question.

OpenLab2010 Submit To Open Laboratory 2010(What’s This?)

1. Indeed they may not even consider themselves to be suffering from anything untoward.

2. You might recognize Omega-3 as representative of this group.

3. For me that number is 5.

4. Remembering the adage: Correlation does not equal Causation.

5. So should the tourism board adopt the slogan “Sweden: You don’t have to be crazy to move here, but it helps”? Too insensitive?


Hedelin M, Lof M, Olsson M, Lewander T, Nilsson B, Hultman CM, & Weiderpass E (2010). Dietary intake of fish, omega-3, omega-6 polyunsaturated fatty acids and vitamin D and the prevalence of psychotic-like symptoms in a cohort of 33 000 women from the general population. BMC psychiatry, 10 (1) PMID: 20504323

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