Oily fish are fish that have oils circulating around their bodies. They are different from white fish (like cod), which store oil in their livers. Sardines, salmon, mackerel, herring, trout and anchovies are all types of oily fish.
Experts recommend eating oily fish once or twice a week to reduce the risk of heart disease1 – but what effect does oily fish have on psoriasis?
What do we know about oily fish and psoriasis?
Oily fish are a rich source of omega-3s, a group of fatty acids that have anti-inflammatory effects2.
After discovering that Eskimos who ate a lot of oily fish had very low rates of heart disease and inflammatory conditions2,3, scientists started to investigate how oily fish might reduce inflammation.
They found the omega-3s in oily fish could reduce the number of inflammatory hormones that the body makes, and lower the expression of inflammatory genes4,5.
Because psoriasis is an inflammatory disease, experts think diets rich in anti-inflammatory omega-3s may be helpful6. Eating oily fish is one way to increase the levels of omega-3 in the body3.
What does the science say?
A number of studies have found that fish oil supplements can help to reduce itching, redness and scaling in people with psoriasis7–10, when taken alone or together with psoriasis medications.
However, lots of these studies have used high doses of fish oil that contain greater levels of omega-3 than are found in oily fish.
This doesn’t mean oily fish isn’t helpful – in one small study from the UK, patients with chronic plaque psoriasis were asked to eat either 170 grams of white fish or oily fish daily for 6 weeks together with their usual psoriasis medications. The patients then switched diets for another 6 weeks.
At the end of the study, the researchers found that the oily fish diet (but not the white fish diet) improved psoriasis severity. The oily fish diet also increased the amount of omega-3 in the body.
In another study from Italy, researchers looked at the relationship between the Mediterranean diet (which includes lots of fish) and psoriasis severity11 in people with mild to severe psoriasis.
They found those who ate the most fish had the lowest psoriasis severity scores. The amount of fish eaten was also linked to the level of CRP, a marker of inflammation.
This doesn’t mean that eating more fish will cure psoriasis, but it does provide clues about the types of eating habits that may be helpful.
Are there any risks associated with eating oily fish?
Some types of oily fish contain high levels of pollutants (like mercury and dioxins) that may be harmful if eaten in large amounts. White fish don’t carry the same risk, because pollutants mostly accumulate in the fatty tissues of animals.
Predator fish like marlin shark and swordfish contain the highest levels, whereas smaller fish like herring, sardines and anchovies contain much less. Women who are pregnant or wanting to become pregnant should avoid marlin, shark and swordfish. All other adults should limit high mercury fish to one portion a week.
Because of the risk of pollutants, the Food Standards Agency in the UK advise that adults eat no more than four portions of oily fish per week12. For women who are pregnant, plan to become pregnant or who are breastfeeding, the maximum is two portions. One portion is equal to 140 grams.
How much oily fish do I need to eat?
In the study from the UK, the patients ate oily fish every day for 6 weeks, but it’s possible that smaller amounts may also be helpful, especially if you don’t eat much oily fish at the moment.
In the Mediterranean diet study13, the researchers found the lowest psoriasis severity scores in people eating fish or seafood more than 3 times a week. We don’t know how much of this was oily fish.
- Oily fish are rich in omega-3’s, a group of fatty acids that can lower inflammation
- Some studies have shown that fish oil supplements (from oily fish) can help to reduce itching, redness and scaling in people with psoriasis
- Eating oily fish can increase omega-3 levels in the body. In one 6-week study, eating oily fish for 6 weeks modestly improved psoriasis severity
- He K, Song Y, Daviglus ML, et al. Accumulated evidence on fish consumption and coronary heart disease mortality: A meta-analysis of cohort studies. Circulation 2004;109(22):2705-2711. doi:10.1161/01.CIR.0000132503.19410.6B.
- Simopoulos AP. Omega-3 fatty acids in inflammation and autoimmune diseases. J. Am. Coll. Nutr. 2002;21(6):495-505. doi:10.1080/07315724.2002.10719248.
- Simopoulos AP. The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases. Exp. Biol. Med. (Maywood). 2008;233(6):674-88. doi:10.3181/0711-MR-311.
- Calder PC. N-3 Polyunsaturated Fatty Acids, Inflammation, and Inflammatory Diseases. Am. J. Clin. Nutr. 2006;83(6 Suppl):1505S-1519S. doi:16841861.
- Ferrucci L, Cherubini A, Bandinelli S, et al. Relationship of plasma polyunsaturated fatty acids to circulating inflammatory markers. J. Clin. Endocrinol. Metab. 2006;91(2):439-446. doi:10.1210/jc.2005-1303.
- Wolters M. Diet and psoriasis: experimental data and clinical evidence. Br. J. Dermatol. 2005;153(4):706-714. doi:10.1111/j.1365-2133.2005.06781.x.
- Ziboh VA, Cohen KA, Ellis CN, et al. Effects of dietary supplementation of fish oil on neutrophil and epidermal fatty acids. Modulation of clinical course of psoriatic subjects. Arch. Dermatol. 1986;122(11):1277-1282. doi:10.1001/archderm.1986.01660230069013.
- Maurice PD, Allen BR, Barkley a S, Cockbill SR, Stammers J, Bather PC. The effects of dietary supplementation with fish oil in patients with psoriasis. Br. J. Dermatol. 1987;117(5):599-606. Available at: http://www.ncbi.nlm.nih.gov/pubmed/3689678.
- Bittiner SB, Tucker WF, Cartwright I, Bleehen SS. A double-blind, randomised, placebo-controlled trial of fish oil in psoriasis. Lancet 1988;1:378-380. Available at: http://onlinelibrary.wiley.com/o/cochrane/clcentral/articles/032/CN-00052032/frame.html.
- Gupta AK, Ellis CN, Tellner DC, Anderson TF, Voorhees JJ. Double-blind, placebo-controlled study to evaluate the efficacy of fish oil and low-dose UVB in the treatment of psoriasis. Br. J. Dermatol. 1989;120:801-807. Available at: http://onlinelibrary.wiley.com/o/cochrane/clcentral/articles/539/CN-00061539/frame.html.
- Barrea L, Macchia PE, Tarantino G, et al. Nutrition: a key environmental dietary factor in clinical severity and cardio-metabolic risk in psoriatic male patients evaluated by 7-day food-frequency questionnaire. J. Transl. Med. 2015;13:303. doi:10.1186/s12967-015-0658-y.
- Food Standards Agency. Oily fish advice: your questions answered. 2004. Available at: http://tna.europarchive.org/20110116113217/http://www.food.gov.uk/news/newsarchive/2004/jun/oilyfishfaq#h_3. Accessed April 12, 2016.
- Barrea L, Balato N, Di Somma C, et al. Nutrition and psoriasis: is there any association between the severity of the disease and adherence to the Mediterranean diet? J. Transl. Med. 2015;13(1):18. doi:10.1186/s12967-014-0372-1.
- Zhang X, Gandhi N, Bhavsar SP, Ho LSW. Effects of skin removal on contaminant levels in salmon and trout filets. Sci. Total Environ. 2013;443:218-225. doi:10.1016/j.scitotenv.2012.10.090.