By Concepta Merry, MB, BCh, BAO, BA

Associate Professor, Global Health, School of Medicine, Trinity College, Dublin

Dr. Merry reports no financial relationships relevant to this field of study.

SYNOPSIS: A study in Ecuador showed a strong positive correlation between dietary oily fish intake and sleep quality.

SOURCE: Del Brutto OH, Mera RM, Ha JE, et al. Dietary fish intake and sleep quality: A population-based study. Sleep Med 2016;17:126-128.

In Arianna Huffington’s best-selling book The Sleep Revolution, which described a global sleep crisis, Dr. Judith Owens, director of the Center for Pediatric Sleep Disorders in Boston, said “sleep is just as important as good nutrition, physical exercise, and wearing your seat belt.”1 Yet, a Gallup poll found that 40% of adult Americans are not getting enough sleep.2 Given the emerging data on the risks associated with poor sleeping habits, integrative health sleep solutions are needed.3

Fish that has more than 5% fat is considered oily fish. Examples include anchovies, sardines, salmon, tuna, and mackerel. Oily fish is a rich source of both long-chain omega-3 polyunsaturated fatty acids (such as docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) and vitamin D.4,5 Both omega-3 and vitamin D are implicated as important players in the sleep/wake regulation cycle.5,6 If we join the dots, then oily fish could be a potential integrative health sleep solution. This theory is supported by a study in male prisoners who reported better sleep on a diet of farm-raised oily Atlantic salmon.7

Del Brutto et al sought to assess the effects of oily fish consumption on sleep quality. The study was carried out in a closed community of adults living in rural Ecuador. Subjects were residents of Atahualpa, a closed fishing village with no shift work or external sources of polyunsaturated fats or fish oil supplements apart from natural fish. The study was part of the ongoing Atahualpa project, which is a population-based study designed to reduce the burden of non-communicable diseases in the region.

The study had a cross-sectional design and involved a door-to-door survey, using a validated Spanish version of the Pittsburgh Sleep Quality Index. A total of 721 Atahualpa residents > 40 years of age were enrolled. Four people were disqualified from the final analysis because of incomplete data collection.

For the purposes of the study, poor sleep quality was defined as a Pittsburgh Sleep Quality Index score of  6. Poor sleep was identified in only 28% of the study participants. Oily fish consumption in Atahualpa is high, with < 5% of the adult population consuming less than two servings per week.

The study found that good quality sleep (Pittsburgh Sleep Quality Index score < 6) was associated with a higher number of mean servings per week of oily fish (P = 0.013). Additionally, the authors found that the Pittsburgh Sleep Quality Index score improved by 9.3% (95% confidence interval, 2-17%) for every 10-serving increase in dietary fish.

The linear relationship that was noted between improvement in sleep quality with increasing intake in oily fish was noted even in people who already take more than the recommended amount of oily fish per week (one to two portions).

In summary, the investigators not only showed a strong correlation between dietary fish intake and sleep quality, but also showed that an increase in the amount of dietary fish intake was associated with further improvements in the quality of sleep. The authors cautioned against overzealous use of oily fish as a sleep remedy, given that excess intake of oily fish could be associated with a high blood level of methyl mercury.

COMMENTARY

This study showed a direct relationship between higher oily fish intake and good sleep quality. The high consumption of oily fish intake in Atahualpa may explain the relatively low percentage of patients (28%) who reported poor sleep quality in the survey. Additionally, the sleep quality index improved with increasing intake of oily fish, even for people who already had consumed more than the recommended amount of oily fish per week.

Study limitations included the fact that the study design did not include blood omega-3 levels or vitamin D measurements. Additionally, because of the cross-sectional study design, it was not possible to fully assess causality. However, the authors noted that it was unlikely that poor sleep quality resulted in a lower dietary fish intake, meaning that reverse causality was unlikely. Therefore, the authors concluded that higher amounts of oily fish consumption are related causally to better sleep quality. This is biologically plausible because oily fish is a rich source of DHA and EPA, which regulate serotonin production. Oily fish is also a good source of vitamin D, which plays a role in the sleep-wake cycle. There are many health reasons to include oily fish in one’s diet, and now it seems that we can add sleep to that list of benefits. Many people are concerned about sleep. Perhaps the results of this study will be a good enough reason for some people to consider including oily fish in their diet.

REFERENCES

  1. Huffington A. The Sleep Revolution. New York: Harmony Books; 2016.
  2. New Gallup Poll on Sleep. Available at: http://bit.ly/2yM6L1F. Accessed Aug. 10, 2017.
  3. Kripke DF. Hypnotic drug risks of mortality, infection, depression, and cancer: But lack of benefit. F1000Res 2016;5:918.
  4. Weichselbaum E, Coe S, Buttriss J, Stanner S. Fish in the diet: A review. Nutr Bull 2013;38:128-177.
  5. Gominak SC, Stumpf WE. The world epidemic of sleep disorders is linked to vitamin D deficiency. Med Hypotheses 2012;79:132-135.
  6. Monti JM. Serotonin control of sleep-wake behavior. Sleep Med Rev 2011;15:269-281.
  7. Hansen AL, Dahl L, Olson G, et al. Fish consumption, sleep, daily functioning, and heart rate variability. J Clin Sleep Med 2014;10:567-575.