Fish consumption and its potential benefits on human health is today an interesting area of research and many studies have found associations between a higher regular intake of fish and improvements in physical- as well as emotional wellbeing.
This article will give a brief background on this topic, discuss why it may be that fish is often associated with higher health scores, both physical and emotional and also highlights some of the research we have today to support the benefits of including fish as part of a varied diet.
Inflammation and its impact on human health
We know today that our physical health affects our emotional wellbeing and that physical health concerns increase the risk of experiencing low mood and developing mental health disorders such as depression.
In turn, mood disorders can have detrimental effects on our physical health.
Evidence is increasingly showing that one of the links between physical- and emotional health problems is inflammation (the gut microbiome is another area but that is a huge topic itself and can also play an important role in the modulation of inflammation) . Inflammatory pathways are pivotal in the pathogenesis of many diseases, including for example metabolic diseases and cardiovascular disease and there is today increased research and attention on inflammation and its role, also for neurological health and subsequently, emotional wellbeing.
Inflammation and the brain
Inflammation and it’s influence and effects on the human brain is today an important topic and an area which is being intensely studied.
Inflammation leads to the mobilization and activation of immune cells as well as the release and activation of inflammatory cytokines, which both, have demonstrated the ability to change mood and behaviour.
Research has shown that pro-inflammatory cytokines may negatively affect the function and the metabolism of neurotransmitters, the neuroendocrine system and the activity of neurotransmitters in the brain.
With neurotransmitters, such as serotonin and dopamine, playing an important role in the regulation of our mood and emotions- any neurological changes and malfunctions in the brain’s signalling system, can have negative consequences. Therefore, targeting inflammation, is important to help keep mood stable. As serious mental health concerns, such as depression, are characterised by low mood, targeting inflammation may therefore have preventative effects both for our physical and emotional wellbeing.
Inflammation and omega-3 fatty acids
One area of research relating the potential modulation of inflammation is that of omega-3 polyunsaturated fatty acids (PUFAs).
There are many research studies demonstrating important health modulatory and anti-inflammatory effects of omega-3 PUFAs and large-scale epidemiological studies have for example shown lower rates of depressed mood as well as lower incidence of chronic illnesses such as CVD in populations consuming diets high in omega-3 PUFAs.
The three most known forms of omega-3 PUFAs are; ALA, DHA and EPA.
Alpha linolenic acid, or ALA, is an essential fatty acid, meaning it can not be synthesised in the human body so we have to get it from our diet.
(Note: There are two essential fatty acids; the second is linoleic acid (LA) which is not an omega-3 but an omega-6 fatty acid).
ALA is mainly found in plant oils such as walnuts, flaxseeds and hemp and gets synthesised by the human body and can be converted after several conversions into DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), but the conversion rate is unfortunately very low and therefore EPA and DHA are often referred to as semi-essential fatty acids.
EPA and DHA can, apart from being synthesised from ALA, also be found in food sources, mainly fish and seafood. As DHA and EPA are the active forms of omega-3, consuming fish and seafood may therefore benefit us more than getting our omega-3 PUFAs from, for example, nuts and seeds, specially for people who have genetic predispositions to have poorer conversion rate from ALA. (Therefore, specially, if you follow a vegan diet, it may be beneficial to consider omega-3 supplementation, there are vegan algae versions, but do remember that supplementation should always be done with guidance from a trained professional, specially when taking medications and it is also essential to look for high quality and fresh products as these oils are prone to oxidation).
DHA and EPA and brain health
Omega-3 PUFAs have been shown to produce powerful anti-inflammatory metabolites, and therefore have the potential to positively effect all aspects of health.
When it comes to human brain health, DHA, is in addition, an important structural building block for phospholipid membranes of the brain (making DHA very important specially for the development of babies and growing children's growing brains). EPA, has less of a structural role but is still highly neuroactive. Studies also indicate that DHA and EPA together can boost our levels of BDNF (BDNF is short for brain derived neutrophil factor, which for example, is responsible for renewal and growth of brain cells).
Therefore, both DHA and EPA have very important roles for our physical and emotional health and including fish (particularly oily fish which have higher levels) on a regular basis may have great health benefits.
Vitamin D
It is easy to mainly focus on omega-3 PUFAs when discussing the potential health benefits of eating fish but it is important to not forget about other nutrients commonly found in fish.
Although omega-3 fatty acids such as DHA and EPA, are believed to play an important role in the potential health benefits of consuming fish, there are other nutrients in fish which in combination, may be important factors. Examples of these nutrients which have been researched for their effects on physical and mental wellbeing are for example B-vitamins, tryptophan (an amino acid which is a precursor to our neurotransmitter serotonin) and vitamin D. Vitamin D is often called “the sunshine vitamin”, a fat-soluble vitamin (also works as a hormone) which the body can synthesise from UVB sunlight and cholesterol (cholesterol is actually the precursor to our steroid hormones, which can partially explain why people following very low-fat diets may see an imbalance in their hormone production). Vitamin D is also found in certain foods with oily fish being one of the best sources. Vitamin D has several functions in the human body and is essential for bone and musculoskeletal health and the research regarding vitamin D and its profound effect on the immune system is booming at the moment and I am sure we will find out a lot more about its mechanisms and functions in a not-so-distant future. Vitamin D has shown to have immune modulating properties by both affecting our innate (immediate) and adaptive (more long term) immune system through regulating pro-inflammatory cytokines and affecting cell signalling. Studies have for example shown that vitamin D has the ability to bind directly to DNA and activate a gene called MKP-1 which helps interfere with inflammatory cascades caused by inflammatory bacteria (in this case LPS) and cytokine production. Several studies are also showing that a wide range of diseases and chronic illnesses as well as mood disorders, are associated with lower blood concentrations of vitamin D, which strengthens the importance of maintaining adequate levels of vitamin D throughout the year.
Research has also shown that people with low levels, who increase their vitamin D levels, may decrease their inflammatory markers and may see a reduction in symptoms of, for example, low mood. One thing which is really important to remember when it comes to vitamin D is that it is a fat soluble vitamin, meaning it gets stored in our body. Therefore high levels of vitamin D can be toxic and it is often advisable to check blood levels before supplementing (specially if thinking of taking higher doses) and working with a practitioner to make sure it is done safely. We don’t know exactly how much time we need to spend outside for our bodies to produce enough vitamin D, it really varies depending on skin type (dark skin needs more time), genetics (there are SNPs which affect how effectively we make vitamin D), where we live etc etc. It is suggested, if living in the UK, that spending as little as 10 minutes outside (without sunscreen) with face, lower arms and lower legs uncovered sometime between the hours of 11-3 pm during summer months (April- September) is beneficial, but these guidelines do of course vary from person to person.
Fish consumption and emotional wellbeing- what does research show?
As previously mentioned, there is today plenty of research on vitamin D, omega-3 fatty acids and their importance for our health and with fish being one of our major food sources, this makes fish consumption an interesting area of research for depression and emotional wellbeing, as well as general health status.
One meta-analysis from 2015, analyzing the results from 26 studies, showed significant inverse associations between high fish consumption and depression. This was valid for both cross-sectional, as well as cohort studies.
One of the most well-known studies is the Japanese Public Health-Centre-Based Prospective study (JHCP Study). This large population study analyzing fish consumption and its potential correlation with depression, took place over 20 years, from 1995 to 2015. Included in this cohort study, were 1181 participants, who during the 20 years, filled out the same food questionnaire on three occasions. This study included both men and women, who were all aged between 63 and 82 at the completion of the study. In 2014-15, the participants were asked to do a mental health examination and the results showed a reverse J-shaped association between fish consumption and depressed mood. This showed that consuming up to 111.1 g of fish per day, compared to not eating fish at all, showed to be protective against depressed mood, but very high intakes of fish did not have this protective effect and was instead associated with an increase in depressed mood amongst participants. One potential reason for this J-shaped result could be the high methyl-mercury content in certain large fish, many of which are popular in Japan.
This study is a great example of a large-scale longitudinal study with participants being followed over a long period of time.
Another population study, examining the potential association of symptoms of depression with consumption of fish is the “Ikaria study” from 2009.
In this study, 673 elderly individuals aged between 65 to 100, filled out a semi-quantitative food questionnaire and the Geriatric Depression scale (GDS with range 0 (worst) to 15 (best) used to assess depression. The results showed that
consuming fish more than 3 times per week (compared to rarely), showed an inverse association with depressive mood.
The 1996/1997 New Zealand Health Survey and Nutrition Survey, which assessed fish consumption and any potential association with self-reported mental health status is another large study showing correlation between fish consumption and emotional wellbeing. In this study, mental health status was measured by the Short Form 36 and later compared to data from the 1997 Nutrition survey. This study included 4644 adults living in New Zealand over the age of 15.
The results showed a significant correlation between self-reported mental health status and fish consumption ( comparing no consumption with any consumption) after including potential covariates.
My independent research study
As part of my Bachelor's degree in Psychology, I conducted a research study to investigate the potential health benefits of consuming fish.
With this study, the aim was to investigate whether self-reported emotional wellbeing and general state of health had an association with the levels of weekly fish consumption.
This Swedish small, cross-sectional, between-group study collected data from participants through an online questionnaire open to people aged 18 and above.
The data from 53 participants, aged between 18 and 75, was used for the statistical analysis.
The majority of the participants were aged between 35 and 44 and out of the 53 participants, 39 were female and 14 were male.
This study used a modified Short form 36 (as used in The 1996/1997 New Zealand Health Survey and Nutrition Survey) with an additional 11 questions, including questions on age, gender, fruit- and vegetable consumption, white- and oily fish consumption, water intake and use of nutritional supplements and special diets.
Most of the questions in the survey were on a scale system. After collecting the information- some of the questions were reversed from 1-6 to 6-1 etc to make sure the answers would not give a misleading and false outcome. The variables from the SF-36 questionnaire were then converted to follow a scale from 0 (worst) to 100 (best), according to the SF-36 manual.
Following this, questions from the SF-36 questionnaire were grouped together in appropriate categories to follow the guidelines and manual of how to use the SF-36 questionnaire.
The eight categories included;
General Health, Physical Functioning, Role limitations due to physical health, Role limitations due to emotional problems, Energy/Fatigue, Emotional wellbeing, Social functioning and Pain.
All the categories, after being given new variables, were on a score from 0-100, with a higher number resulting in a more positive outcome. For example, a score of 80 in the pain health category meant that the person had less pain than a participant who scored 20.
These different Physical and Mental health score groups were then used to perform correlation and multiple regression analysis, to analyse any potential correlations with variables such as age, gender, oily- white and combined fish consumption, vegetable, fruit and water intake as well as nutritional supplement use and special diets, such as choosing to follow a vegan/ vegetarian or pescatarian diet.
Earlier research in emotional wellbeing and mental health have highlighted differences in results taking into consideration gender and age. Depression is, as an example, more represented amongst women. For this reason, age and gender were included as covariates in the multiple regression analysis.
The study showed a weak (close to moderate), but significant (r= .29, p < .05) correlation between oily fish consumption and general health status (overall physical and emotional health). The means general health scores were 4.3 points higher for participants who ate one to two portions of oily fish per week, compared to participants who ate less than one.
When using multiple regression analysis to include the coefficients age and gender- the association was still significant at p < .01
No correlation was found between white fish- or combined fish consumption or any of the other foods looked at in this study in correlation with the health categories included.
The study also showed a moderate, significant correlation between gender and emotional wellbeing scores at (r= .34, p < .05), meaning in this case, that women reported on average 8.09 points lower in emotional wellbeing scores compared to men.
There was a statistically significant positive correlation at a moderate level between combined fish consumption and vegetable consumption (r= .33, N=53, p <.05, two tailed).
However, no significant correlations were found between oily fish consumption and either vegetable- fruit, water, or supplement intake.
In addition, there were no found significant correlations between vegetable consumption, fruit- water or supplement intake and the 8 different health categories.
It also found a near significant correlation between oily fish consumption and emotional wellbeing specifically (p < .059) but based on a p value of .05 or lower, this was not statistically significant.
The results from this small study does indicate that oily fish, may potentially have a more profound impact on health and wellbeing scores and that further research
would be recommended to look at this in more detail.
All data was reviewed and confirmed both by an examinator and a mentor as well as peer students to make sure the results were accurately reported. It is however important to note that this study was in no way perfect and there are several areas for criticism to keep in mind when looking at the results, some of these are;
This was a small study with only 53 participants so the power of the study was therefore not enough to make any assumptions of the outcome.
This data was collected from participants during March and April 2020 at a time of great uncertainty, which may also have affected the outcome.
The fish intake of the participants in this study were also very similar with no participants reporting weekly intakes in excess of 2-3 times per week and it would have been interesting to see if the results had been different when looking at higher weekly intakes of fish.
A large majority of the participants were of similar age, which is important to remember as this means that this study may not be representative for older or younger age groups.
The results from this small, Swedish study therefore indicate that more large-scale studies need to be undertaken to further investigate the potential correlation between fish consumption and self-reported emotional and physical wellbeing.
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